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73-87 Chevy _ GMC Trucks => Interior & Equipment => Instrumentation => Topic started by: sgrinavi on April 10, 2022, 06:30:37 AM
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Hi guys, I have an 81 K20 5.7 manual that's giving me a fit regarding the instrument panel.
For starters, I have the dreaded no-gauge light issue - changed the light switch, no help. Started to follow the guide (here http://forum.73-87chevytrucks.com/smforum/index.php?topic=26558.msg221363#msg221363 (http://forum.73-87chevytrucks.com/smforum/index.php?topic=26558.msg221363#msg221363) ) and found that I don't have power on either side of the inst. fuse but do have it at the dark green wire on the light switch.
EDIT - I have power on the dark green side of the INST. fuse, but nothing on the "red" side (assuming it's supposed to be gray?) (See attachment)
Pulled the dash apart and peeled about 30 feet of electrical tape off the harness(s) and found some oddities - (see attached) . I cleaned up the connections, but didn't attempt to figure out what they were doing, I'm guessing a radio, but the one that was installed was not hooked up to anything.
The other intermittent issues that may, or may not, be related. The wipers work sometimes (I changed the switch, no help), the brake light comes on sometimes, the seat belt buzzer/light comes on sometimes. Directional light indicators always work as all the exterior lighting. My dome light doesn't work, but I haven't really looked at it.
The ground seems to be good; I've used for testing and it hasn't been flaky.
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EDIT - Figured out how to split the box. DUH.
I tried to pull the fuse block off the fire wall to see if I had some corrosion on the back side, but can't seem to get it apart, the screws come out and it's loose, but I can't seem to get to the back side of it. Does it split apart somehow?
Does it sound as though all my issues are related?
Any idea what that random yellow wire is for?
EDIT, The red wire comes from the INST. fuse (opposite the dark green)
Any idea what I need to do to straighten out that red/gray splice?
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The gray wires is probably your dash lights and the red wire should not be twisted with them. The multiple black wires spliced together is normal and is a factory ground splice.
PS: The two red wires in fuse panel is probably OK, There are a couple places something like that occurs. Take a look at the wiring diagrams supplied on this forum.
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Thanks for the response.
I've been digging at it some more - The red wire on the back of the fuse block is the one that is twisted with the three gray wires in the previous photo and is opposite the dark green on the INST. fuse. According to the wiring diagram that should be a gray wire and should terminate at the instrument panel plug
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Hi guys, I have an 81 K20 5.7 manual that's giving me a fit regarding the instrument panel.
EDIT - I have power on the dark green side of the INST. fuse, but nothing on the "red" side (assuming it's supposed to be gray?) (See attachment)
EDIT, The red wire comes from the INST. fuse (opposite the dark green)
You are correct that the red wires from the INST fuse substitute for gray. The pictured "twisted" splice of red to gray wires is not factory, suggesting that the harness is aftermarket and/or otherwise jury-rigged.
Burnish the INST fuse contacts in the fuse block. You can accomplish the task by smearing some fine grit valve grinding compound onto the blades of the old fuse then repeatedly insert and withdraw the fuse. Rinse the fusebox contacts after burnishing using WD-40, blow the fusebox "dry" using compressed air, and then install a new 5-amp INST fuse. You may need to burnish other fuse sockets, similarly, to help solve intermittent power delivery issues. Severe oxidation of blade-type fusebox contacts is not particularly common but can be confounding when it occurs. In contrast, glass cartridge-type fuse boxes were plagued with oxidation issues.
At least one of the gray wires should route to the I/P cluster connector. If not, you will need to correct that to establish cluster illumination.
The dangling yellow and black/white wires may have been power and ground for an aftermarket radio and subsequently abandoned. You will need to trace those wires to determine where they connect.
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Here is a pic of the fuse block
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Thanks guys!
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Well, I cleaned up the fuse block and replaced all the fuses and the bulb for my wiper light came on. Woot. Which happens to be the only, known, working bulb since I just replaced the switch. I'm going to replace the rest of the bulbs. Also, the seat belt buzzer is working as well.
Now the bad news, when I put a fuse in the horn terminal on the fuse box the horn started blowing and now my dash turn signal indicators are not working, but the turn signals are fine.
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The horn relay is constantly powered from B+ and grounds through the horn button on the steering wheel. Unplug the turn signal switch connector along the right side of the steering column behind the dash to see whether the horn stops sounding. For the cluster turn indicators to be affected by the horn, the cab grounds are suspect. Validate the cluster and I/P harness grounds to the cab and the cab to the B- post of the battery.
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Sorry to be so late getting back, pesky work and life get in the way all the time.
Anyhow, when I disconnect the directional stalk connector the horn does stop blowing, I ran a new ground from the battery to the block in the cab by the fuse panel that all the ground tie into. No change.
SO, another interesting symptom that might be useful. When I turn the rheostat on the light switch the fuel gauge moves.
Thanks for all the help
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The horn blowing constantly is caused by a problem in the steering column (e.g., the black horn wire is chafed, pinched, or otherwise grounded inside the column, the turn signal switch is faulty, or the horn contacts are shorted from distortion or something incorrectly assembled).
The other electrical symptoms, as you describe them, are related to floating grounds or improper wiring. Check/burnish all of the ground connections, including the I/P harness connections to the PCB.
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So I pulled the steering wheel and removed the turn signal harness, the black wire is perfect. Before I re-assembled it, I put the horn fuse back in to see if I could get it to work. The horn starts blowing when I put this green ring back on - it's grounding to the steering shaft. Is that correct?
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That green turn signal canceling cam has a brass ring that connects the copper brush protruding from the turn signal switch to the horn contacts above the steering wheel via a 1" long spring and aluminum pin. It sounds like the brass ring of the cam is grounding; it shouldn't. Take a close look to figure out where/how it's grounding.
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I replaced the canceling cam, the turn signal switch, and put an aftermarket steering wheel on the vehicle. The horn works now, but there are still lots of issues.
- No instrument lighting other than the wiper switch and another random light that's disconnected behind the dash.
- When I operate the dimmer rheostat (new light switch) you can hear a slight buzzing noise that gets louder as the lights get brighter
- When I turn the two functioning dash lights off via the light switch the buzzing stops.
- When I use the turn signals, while the lights are on, the buzzing noise changes pitch, and the two functioning lights (as well as the brake light) will actually dim slightly with the blinker lights
- The interior right turn indicator no longer functions
It all seems so random and odd.
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Could have a circuit board (I had changed mine) on the back of the gauge cluster that is bad. Other than that you may have to pull out and completely go through your interior cab wiring harness wire by wire to ensure all is OK. I did it with mine recently and replaced some wires, connectors, and cleaned all my terminals.
VZ, bd, and some others are really good and may have some better information.
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Thanks, Mike, how did you determine that you needed to replace the circuit board?
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Some of my gauges and lights did not work properly and when I took a look at the back of the gauge cluster (at the circuit panel) I saw dark spots that appeared to have overheated and there were areas that did not appear to have good contacts. They are thin and can easily get damaged and sometimes you can get a bad new one as well. I have a spare I keep now just in case.
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Well, after taking the dash apart, again, I have a, single, dash light so I'm assuming all is well with the wiring and it's just the board.
Time for a new instrument panel. WOOT - I have a New Vintage USA on order. I was going to just do the tachometer upgrade kit from , but it's back ordered and they couldn't tell me when I might get it. I could have put the same kit together from parts, but it was expensive to do. Seemed easier to get all new sensors and new tech gauges for a couple hundred more.
Thanks for all your help!
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SO, another interesting symptom that might be useful. When I turn the rheostat on the light switch the fuel gauge moves.
Thanks for all the help
That exact issue is how I found this forum in 2004. My circuit board was bad in back of the speedometer cluster. I couldn't see it but changing the cluster from a donor truck fixed the issue