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73-87 Chevy _ GMC Trucks => Electrical => Topic started by: 78C10 sleeper on May 17, 2013, 12:14:39 am
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None of the rear lights on my 78 C10 are working. And I have checked the fuses,flasher,head light switch and brake light switch and I replaced the turn signal light switch.the truck used to be a 6 cylinder and some of the wiring is hacked and it has extra wiring electric fuel pumps nitrous electric fans ect any help would be very much appreciated thanks
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The first thing to think any time there is an electrical problem on a vehicle is "I wonder if there is a ground problem." Two reasons: 1) we almost always think in terms of the hot lead (fuse, switch, etc.), ignoring the ground, and 2) it usually is the ground.
The two critical grounds on the 78 C10 are 1) the ground strap from the firewall to the rear of the passenger-side head on the engine and 2) the ground from the front of the driver-side head of the engine to the frame rail. These are copper braids with an eye on each end.
If those aren't there, just about anything can happen electrical in the truck, like headlights flashing with the turn signals and such. And these straps are often left off when people do work on these trucks.
So check those first.
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I did check the ground on the back of the head but it does not have one on the front of the head also it has a ground that goes from the tail light bucket to the bed but on the passenger side there is none is that correct that for the reply
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There has to be a ground strap from the power steering bracket upper bolt to the top side of the frame rail about even with the back of the steering box. Right now both your cab and engine have intermittent ground, or things are finding ground paths in weird ways.
With regard to the rear lights, there should be a sheet metal ground on both sides. See: http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/77-80_chass_rr_light.jpg
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Its manual steering. Im going to buy a strap today where should I place the strap on the motor would the head or an avalible hole in the block be ok
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Did you check the bulbs...
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there doesnt have to be a ground from the pump to the frame. there is usually one on the alt bracket to bat/frame. but have you done anything lately to the truck?
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Yes the bulbs are new and I did put a new cable from the alt to the bat when I installed the motor about 4 years ago.and yes I've done a few things to it put a turn signal switch and some new electric fuel pumps
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Re: the engine ground strap: There's a screw on the top side of the frame rail about even with the rear of the steering box. That's one end. The other can go to the outside front valve cover bolt.
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theres allot of screws on my truck allot of loose screws including the one behind the wheel lol. but not saying that one is not supposed to be there just saying that one is not necessary. although i never heard of a problem with having too many grounding straps. sorry about the last edit to my last post but the grammar was killing me and i wrote it lol
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He's also missing the sheet-metal ground on one side, and that won't help either.
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Its been raining all day >:( haven't ben able to work on it and also one head light has always ben brighter then the other could that be a ground issue to thanks for the help
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Yeah, there should be a ground from the headlights harness on both sides as well, as shown in this diagram. One is listed as frame ground, the other as sheet metal ground.
http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/77-80_250_I6_eng_frt_light.jpg
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Ok so I redone the missing bed ground and now the lights work when the head lights are on but not when there off and the signal lights wont blink
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Signal won't work with the headlights off. Might be flasher swap flashers and see what happens
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Tryed a flasher didn't help I just put a turn signal switch in it could it be installed wrong I mean it was pretty strait foward
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ok let me understand the lights (im guessing running) work with the headlight on but if the headlight are off they wont work? and the rear lights turn on when you turn the headlights on? what about 4 ways?. i had a problem with the pig tail on my switch on the steering column it had to be just right for it to work but i was also using a 80s steering column on a 74 wire harness
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Yeah, you need to give us a little chart of what works when and what doesn't. Something like this example:
Headlights on
- tail lights are on
- turn signals work
- flashers don't flash
- brakes light up brake lights and front signals
Headlights off
- tail lights are off
- turn signals don't work
- flashers flash
- brakes light up rear lights only (i.e. correct)
Gives us something like that and I betcha we can figure it out.
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Ok new flasher didn't fix it think I may pull the steering wheel tomorrow check out the components under there what do u guys think?
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Ok new flasher didn't fix it think I may pull the steering wheel tomorrow check out the components under there what do u guys think?
This..........
Yeah, you need to give us a little chart of what works when and what doesn't. Something like this example:
Headlights on
- tail lights are on
- turn signals work
- flashers don't flash
- brakes light up brake lights and front signals
Headlights off
- tail lights are off
- turn signals don't work
- flashers flash
- brakes light up rear lights only (i.e. correct)
Gives us something like that and I betcha we can figure it out.
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complete that check list by rich and see where you are
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Ok did the check list so with the head lights OFF I only have brake lights.with the head lights ON I have brake lights and power to all lights except the back up lights because I havent wire them up to my shifter.but either way the signals wont blink. The four ways work in the cab but not at the rear of the truck my front signals have power but they don't blink.
On a side note my high/low beam switch is Geting hot could that be the cause
thanks alot guys for all ur help
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what about running lights? its the first click on the headlight switch
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Yes they the running lights work
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Ok did the check list so with the head lights OFF I only have brake lights.with the head lights ON I have brake lights and power to all lights except the back up lights because I havent wire them up to my shifter.but either way the signals wont blink. The four ways work in the cab but not at the rear of the truck my front signals have power but they don't blink.
On a side note my high/low beam switch is Geting hot could that be the cause
thanks alot guys for all ur help
- If the headlamp dimmer properly switches between high and low beam, check for poor (corroded or loose) connections at the dimmer switch. The dimmer switch will not impact the rear lights.
- Did you replace one or both flashers? Upper (hazard) or lower (turn)?
- Switch the ignition ON and turn signals ON (either direction), then use a test light to check for power at the yellow and dark green wires entering/exiting the turn signal switch connector under the dash at the right side of the steering column. With the turn signals ON you should see power at the yellow (on left turn) and dark green (on right turn) wires. If not, then check for power on the purple wire at the same turn switch connector - it should be 12 volts whenever the ignition is ON, regardless of the turn switch position. Post up what you find.
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Ok I will check that tomorrow and I didn't relize there where to flashers I only replaced the one on the fuse box where is the other one located?
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Both flashers plug into the fuse box. The turn flasher is located at the bottom right corner, the hazard flasher is located at the top left corner.
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Note two flashers in this pic: http://www.rowand.net/Shop/Tech/images/GMATOStyleFuseBlock-Front2.jpg
The wiring diagram shows the two flasher locations on the fuse block: http://www.73-87chevytrucks.com/techinfo/wiring_diagrams/77-80_instrument_pg2.jpg
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My fuse box looks totally different it is the old style with glass fuses but I only see one flasher in the top left hand corner but in the bottom left hand corner there looks like there is a place where one could possibly go....thanks
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Ok so I checked the wires going up the column the yellow, dark green,and purple have no power the only wires that do is a brown one and a black one
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On that style fuse box, the flasher at the top left is the hazard flasher. The turn signal flasher is a divorced type that plugs into a two-wire connector hanging loose out of the harness. It will have one dark blue and one purple wire running to it. It sounds as though the turn flasher is either faulty or missing entirely. Look around the driver side under the dash and you should be able to find it.
The black wire is the horn circuit and the brown wire is from the hazard flasher.
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I found the flasher and checked the wires the red and black have power the green wire dosent even with the turn signal switch on. Is this consistent with a bad flasher or is it just best to replace it
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I found the flasher and checked the wires the red and black have power the green wire dosent even with the turn signal switch on. Is this consistent with a bad flasher or is it just best to replace it
Red, black and green... three wires? Are you sure you're not looking at the horn relay?
The turn flasher will have two wires, dark blue (ignition power) and purple (to the turn switch). The hazard flasher and the turn flasher are the same part number, so will appear similar in shape and have only two terminals.
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This hangs down beside the fuse box its square I don't see any kind of component that look like the other flasher (hazard flasher) there is only the one round component om the fuse box it may be missing Idk thanks
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Post a pic of the fusebox.
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I tryed to upload one it says its to big sorry im new new to this whole thing is there another way to post it
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Go here for a "How to" to resize pics (http://forum.73-87chevytrucks.com/smforum/index.php/topic,6428.msg33935.html#msg33935). You can also use MS Office Picture Manager packaged with some computers, etc.
I agree, post some pics of the fusebox and up around both sides of the column. The turn flasher might be missing, but unless someone removed the connector, you should be able to locate the plug under the dash. As I recall, some vehicles had them clipped upside down to the sheetmetal behind the dash panel somewhere left of the ashtray. You may have to lay on your back and look up. The flasher can be metal or plastic.
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I wont be able to access a pc for the next few days im on my phone. But tomorrow im going to try and trace the wires to find it I will post the pics as soon as I can get to a pc
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Ok guys I found where the flasher goes :D I traced to purple wire back to the fuse box but one of the spade connectors had came out or had ben removed so I traced the green wire and put it back in the fuse box now the flasher Is working both ways and the green arrow lights in the dash are working but the rear lights still don't blink thanks
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Now, we're back to this.....
- Switch the ignition ON and turn signals ON (either direction), then use a test light to check for power at the yellow and dark green wires entering/exiting the turn signal switch connector under the dash at the right side of the steering column. With the turn signals ON you should see power at the yellow (on left turn) and dark green (on right turn) wires.... Post up what you find.
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Ok I have power to the purple and yellow but not the green
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Also the flasher seems a little slow to me
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As you know, the purple lead comes from the turn flasher; it's power into the turn switch. The yellow lead is power out to the left rear turn/stop lamp. Green is power out to the right rear turn/stop lamp. Since the brake lights work, and they share the rear wiring with the turn signals, when you have power on the yellow wire (during left turn), you should observe the left rear lamp brightly illuminate.
However, yellow should be 'hot' only on left turn or with the 4-ways ON. Is this the case?
If the green wire is not 'hot' with the right turn signal ON, replace the turn switch.
A 'slow' flasher may be due to insufficient load, because the rear lights aren't working.
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There's a caveat: Using a voltmeter, check for power on the dark green and yellow wires at the turn switch connector with everything turned OFF, except the tail lights. Make sure the running lights are ON when you do this. Post the reading.
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Ok tested the wires and the green and yellow have power and blink with good voltage but the purple has no power
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You paint a puzzling picture . . .
Ok tested the wires and the green and yellow have power and blink with good voltage but the purple has no power
You realize that this ▲ ▲ ▲ ▲ contradicts this ▼ ▼ ▼ ▼
Ok I have power to the purple and yellow but not the green
To measure power on yellow and dark green, you have to have power on purple! Purple is the power source for the 'yellow' and 'dark green' wires, via the flasher and turn signal switch.
You're telling us, now, that the rear turn lamps don't flash, but the yellow and dark green wires 'blink,' and the brake lights work properly.... This doesn't logically follow, because the same wires that feed the brake light filaments, also feed the turn signal filaments (since brake and rear turn lights share the same filaments). Because the brake lights work, we know that the wires coming from the turn switch are unbroken all the way through to the rear lamps. So, when the wires 'blink' at the switch, the rear turn lamps should 'blink' as well. Follow?
You still may have poor grounds or there may be a problem with the bulbs and/or sockets(?).
Do the following:
- Do this test again.... You'll actually be evaluating the ground with this test. Using a voltmeter, check for power on the dark green and yellow wires at the turn switch connector with everything turned OFF, except the taillights. In other words, make sure only the headlights/running lights are ON when you take these voltage measurements. You're not checking flasher operation this time. Post the readings.
- Verify you have the correct (1157) bulbs installed and that they're installed correctly according to the offset tangs/pins.
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Ok sorry I have a new development the left brake light only comes on when the head light switch is on and it does not brighten when the head light switch is on but the right brake light works correctly and brightens with the head lights on . The brake light bulbs are correct. Sorry for the confusion this electrical trouble shooting is very confusing and new to me lol
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Ok sorry I have a new development the left brake light only comes on when the head light switch is on and it does not brighten when the head light switch is on but the right brake light works correctly and brightens with the head lights on . The brake light bulbs are correct. Sorry for the confusion this electrical trouble shooting is very confusing and new to me lol
When you say right and left, do you mean from the front or the back? Better is to say driver's side or passenger's side. Reason I ask is that you previously said that there was no sheet metal ground on the passenger's side, but there was on the driver's side. Has that missing sheet metal ground been installed? Has the sheet-metal ground on the driver's side been checked for good continuity to ground?
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Left being driver side eight being passanger side is what I mean and the missing ground was replaced. And the drivers side ground was just cleaned free of rust and reinstalled I have never continuity on anything before but I do have a meter to do so
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Electrical repair isn't especially difficult, it just seems 'mysterious' because you can't directly see it. You can only observe its effects.
Describe exactly where each ground wire between the bed and frame is attached to the frame, for example, the left bed ground is attached to__________, the right bed ground is attached to__________; fill in the blanks (left frame rail, right frame rail, crossmember, etc.).
Now, run a temporary jumper wire between the attachment points where the ground wires fasten to the frame. Tell us if there's any change in the function of the lights.
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Well the driver sides one is a factory ground that is connected to the sheet metal of the bed just behind the tail light bucket.the passenger side was missing u could tell it had ben tampered with so I replaced it as factory like as possible with a 12 gage wire both are clean and rust free metal to metal
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Okay. What I'm asking is, where do the bed grounds attach to the frame? And, did you run the temporary jumper?
Here's why:
Typically, only the right frame rail is physically grounded directly to battery through a strap or cable. The left frame rail grounds to the right frame rail through the various riveted/bolted crossmembers and bed attachments. This method of grounding serves adequately when a vehicle is new. But, with use the frame flexes and moves. Water and salts attack the steel. As loose rivets/bolts and accumulated dirt, rust, etc. degrade structural attachments and the resulting ground connections between the various frame members, the frame members become electrically isolated from one another and from the battery. Any appliances 'grounded' to those frame members will then "float" above ground, partially or entirely isolated from battery negative. Under such circumstances appliances will cease to function entirely; or they may find alternate (unintended) paths through neighboring appliances. Weird symptoms develop. Rich Weyand explained this near the beginning of this thread.
Back to your problem:
Assuming that the right side ground connection is satisfactory, by installing a temporary jumper between the two grounding points to the frame, you will circumvent any poor electrical connections between the frame members and eliminate the resulting 'floating' circuits.
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Ok so I ran a jumper ground wire to the frame and it didn't help but I checked the front lights are they are all working as they should including the side marker lights. I also check all of the rear lights and the ones that are working only have around 10 amps but at the connector on the steering column all wires have around 12.5 is this acceptable?
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What he said was to run a jumper across the truck, from the ground wire on one side to the ground wire on the other.
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I was under the truck and saw the some wire had ben cut there yellow,red,brown,and black what do they go to?
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Ok ran the jumper wire from side to side still didn't help
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You're going to need a test light, a voltmeter, and a patient assistant.
- Set your voltmeter to the 20-volt DC scale and connect the negative lead of your voltmeter to the battery negative post and the positive lead of your voltmeter to clean, bare metal on the right frame rail. Switch the headlights ON and step on the brake. The meter should register "zero" volt. Does it?
- Repeat the process between battery negative and the left frame rail. The result should be "zero" volt. Is it?
- Remove the left tail lamp lens and bulb. Verify there's no corrosion inside the socket. Turn the headlights ON and probe the two bulb contacts inside the socket using a test light. Be careful not to short either contact in the base of the socket to the metal case of the socket with the test light probe. One contact should test "hot" and one should test "dead." Is this true?
- Now, switch the headlights OFF, switch the ignition ON, and switch the left turn signal ON. Reprobe the socket contacts using the test light. The contacts should test "opposite" to Step #3. Do they?
- Reinsert the bulb. Switch the headlights AND left turn signal ON. Using the test light, probe the metal case of the socket. Does the test light illuminate, or did the tail and turn lights start working correctly?
- If your answer to Step #5 is "Yes," unbolt that lamp from the bed and inspect the backside of the socket for a brown wire (taillight), yellow wire (turn/stop light), and black wire (ground). The black wire is of prime interest. The black 'ground' wire should splice together with two additional black ground wires and then fasten securely to the bed sheetmetal. If the black wire is missing, broken, or making poor contact with the case of the socket, or if the black wire is not connected to clean, bare sheetmetal, you'll need to repair that for a proper ground connection before continuing.
- Repeat the process on the right side.
Go through each step and post your answers to each question - that's five answers per side.
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Like he said! Excellent debugging plan from bd. I forgot about those stupid splices. In the "look first where the light is best" mode, I would probably check the connectivity of the socket ground through to the frame rail first, to make sure that splice is ok.
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I was under the truck and saw the some wire had ben cut there yellow,red,brown,and black what do they go to?
also where did you see these wires? besides under the truck
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The cut wires are behind the bumper (roll pan) rite in the middle it looks like maybe a hacked up trailer harness maybe
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...it looks like maybe a hacked up trailer harness...
X2
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ok I did the check list
with the negative lead on the volt meter on the BAT with head lights on and brake lights on
#1the pass side no voltage
#2 drivers side no voltage
#3
pass side both are hot
driver side both are hot
#4 with head lights off and left turn signal (drivers side light) on both are hot
with right turn signal on only one is hot (pass side light)
#5
no voltage or change on either side
#6
both grounds are clean and rust free I had to replace one a while back
also with the head lights off both the pass and drivers side blink at the same time. the front does the same. with the lights on all the rear lights are on (exept the back up lights) but do not blink front lights don't blink either
thanks for all the help guys
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Don't make any assumptions during the diagnostic process. Be sure to follow instructions explicitly and answer questions the same way. The process is drawn out, because we're addressing the problem "over the phone." An electrician on site would have an answer within about an hour. It's more difficult the way we're going about it, because instructions have to be interpreted then precisely executed, communicated and reinterpreted. And, so it goes, back-and-forth. Our responses are based on your responses. Don't get discouraged...
- Look at the filaments of an 1157 or 1034 bulb. One filament is heavier (thicker) than the other. The thick filament is for turn/brake, the thin filament is for park/taillights. Remove the lenses/sockets from the two front and two rear lamps, so you can see the filaments of all the turn/park bulbs while they are still inserted into their respective sockets. Switch ON the park lights. Carefully inspect each bulb and post by LF, RF, LR, RR which filament is illuminated at each corner of the truck.
- Now, remove the front turn/park bulbs from their sockets. Is there any change in how the rear lamps function?
- The rear turn & brake lamps started functioning correctly - There's a problem with the forward lamp bulbs, sockets or socket grounds.
- The rear lamps function the same as before - There's a short in the wiring between the turn (or brake) and taillight circuits, or a short in the rear socket(s).