no rear lights

[bd]

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.

[78C10 sleeper]

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

[rich weyand]

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?

[78C10 sleeper]

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

[bd]

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.

[78C10 sleeper]

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

[bd]

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.

[78C10 sleeper]

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?

[rich weyand]

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.

[78C10 sleeper]

I was under the truck and saw the some wire had ben cut there yellow,red,brown,and black what do they go to?

[78C10 sleeper]

Ok ran the jumper wire from side to side still didn't help

[bd]

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.

[rich weyand]

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.

[Irish_Alley]

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

[78C10 sleeper]

The cut wires are behind the bumper (roll pan) rite in the middle it looks like maybe a hacked up trailer harness maybe