1984 GMC

[Justin Macias]

Alrighty, i got my 84 gmc last month and its my dream vehicle. But.... I have electrical issues. I dont have any tail lights, no dash lights, with my headlights off my right turn signal works but my left turn signal turns on the hazards and the hazard button pushed in makes all my turn signals and hazard lights stop working. With my headlights on my right turn signal still works but my left turn signal doesnt work at all and neither does my hazards. Needing help so i can get it fixed and legal. Fuses are good and ive checked all the grounds i could find. Thank you for the help.

 

[Jrgunn5150]

I'm guessing the multifunction switch in the column has gone bananas.

 

[1987 GMC Jimmy]

Possibly a pinched or frayed wire somewhere causing the taillights and dash lights issue. I had a pinched tail light wire near the back where your spare tire would be that caused the same issue. The multifunction switch sounds like a logical explanation, too.

 

[chengny]

Alrighty, i got my 84 gmc last month and its my dream vehicle. But.... I have electrical issues. I dont have any tail lights, no dash lights, with my headlights off my right turn signal works but my left turn signal turns on the hazards and the hazard button pushed in makes all my turn signals and hazard lights stop working. With my headlights on my right turn signal still works but my left turn signal doesnt work at all and neither does my hazards. Needing help so i can get it fixed and legal. Fuses are good and ive checked all the grounds i could find. Thank you for the help.

That's a lot of problems. The best first step in this diagnostic would be ( for me anyway) to completely isolate the rear lighting harness from the rest of the electrical system. You could try just unplugging the rearmost portion of the harness first. Look around up behind the bumper/frame and locate the 4-pin Weather-tite connector that leads to the L&R taillights and plate lights:

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Here is what the final section of the harness looks like when it's laid out:

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Test the front/dash lighting. Of course you won't have any rear lights, but if things improve you will have a place to start looking for wiring problems.

If the front/dash lighting show no improvement, consider removing the entire rear lighting circuitry - from the firewall back. If you haven't done this before, it may seem drastic but it's actually easy.

Here are the leads that feed the rear lighting circuits. There are only 4.

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From the top down, the circuit that they service:

1. LT GRN = Back Up Lights

2. YEL = TS & Brake lights (LH) (both circuits share one filament in the two filament bulb)

3. DK GRN = TS & Brake lights (RH) (share a filament in the dual filament bulb)

4. BRN = Parking, Marker & License Plate Lights

This is the bulkhead harness connector ( the sector with the pins for the rear lighting is traced in yellow):

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And this what it plugs into:

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There is a 1/4" bolt with a 3/8" head that holds the male plug securely into the female socket. Unscrew it and pull the male plug from the female socket - which will remain securely fastened to the cab side of the firewall.

Continued...

 

[chengny]

If you look at the image of the male plug you will notice that it is made up of 3 sections. These sections can be separated. But you don't even have to separate all the sections, all you want to do is remove and set aside the rear lighting section. It is the smallest and easiest to remove because it is on the outside. The big section has two arms that capture the other two sections and keep them together. Follow the instructions below and pull the rear lighting group out. Then as suggested above, just set it aside:

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Push the plug back into the socket and lightly tighten the through bolt.

You will now have a fully operational electrical system - except that the complete rear lighting system will be isolated. Test the remaining lighting circuits and see if there is any improvement. The e-flashers and directionals won't act right due to the loss of half the load on the flashers - they will probably blink very fast.

If that doesn't show any improvement, you could try the same test but this time do it with the middle section removed and the rear lighting section back in. The block in the middle contains the pins that connect to the forward lighting (also the horns, windshield washer pump and brake warning light). The rear lighting should be plugged in during this test to provide a load - and also provide something to compare the previous test with.

These are only initial diagnostic steps and they might not reveal anything. And even if you find that - for example - removing the rear lighting harness does cause the rest of the system to act normally, you still will need to zero in on the exact problem. But doing it this way is much easier than tearing into the harness blindly or opening up the steering column.

If you come back and report your results, I'm sure someone will help you either define the problem more closely or suggest some other things to check.

 

[75gmck25]

When there are that many lighting problems it usually means there are problems with grounds.

Start out with checking the instrument panel ground up under the dash, which is either grounded to a post on the emergency brake mechanism, or to a ground block mounted under the dash.

Then check grounds in the engine compartment:
- ground wire to radiator support above each headlight. On the passenger side it also has a pigtail to the negative battery cable
- negative battery to alternator bracket (large diameter battery cable)
- engine block to top of frame (usually on passenger side near the fuel pump)
- engine block to firewall (usually on passenger side near the back corner of the valve cover)

Also check lighting grounds:
- White wire grounded to frame/body in the back, right in the middle of the truck up behind the bumper
- Ground wires at each tail light and front marker light

If you remove the small metal dash panel right under the steering column, you can see the bottom of the steering column. This is where the actuator rod from the ignition switch connects, and it is where all the column electrical wires connect. If you unplug this connector you can get fairly easy access to troubleshoot to the steering column and turn signal wiring withoug having to cut any wires.

Bruce

 

[Charlie]