A Wiring Conundrum

[StevoandaRedK5]

So the one thing that stands between me and my truck being back on the road are the lights. I have printed out the wiring diagrams, but the PO has hacked the harness into a barely identifiable mess. Here's a rundown of what's happening right now:

This stuff works:

• Headlights
• Parklights
• Left Rear Running Light
• Left Turn Signal
• Front & Left Rear Flashers

Here's Most of the Problems:

• Left Turn Signal Causes both front lights to flash, but the taillight works
• Right Turn Signal causes both front lights to blink, but no rear signal
• Right Rear Brake Light not full brightness
• With brakes applied, turning on flashers causes the parklights to come on but not blink, still no right rear

I am fairly sure that there is some shorting going on at the turn signal lever, so that might be the cause of some of it. Any other ideas/tips/solutions? Because I'm am becoming increasingly frustrated trying to diagnose and repair this stuff.

 

[dyeager535]

Can't help much, but emergency light blinking stops when you hit the brakes, at least on GM vehicles of this vintage.

I *think* grounds are a likely issue when other lights operate at the same time others are supposed to. You've double/triple checked that you have the right bulbs in the right sockets? That will lead to weird reactions from the bulbs, usually fast dash turn signal indicator.

 

[lectric80]

Grounds and bulb placement is critical first check. From there I would be looking into the turn signal switch, since brake light signals are all routed through the switch. If the wiring is as hacked as you are saying, I would be looking at rewiring all the light systems to solve the issues, but not until you verify where the problem is.

Check the bulbs and grounds first. Then test the turn signal switch harness, where it comes off the column. You want to make sure signals are being sent appropriately when the switch is placed in each position. You also want to verify that the brake light signal is clean when it leaves the switch.

Once you get that tested I would seriously consider running all new wires directly from the turn signal switch to each socket. This will solve the problems created by the PO, as well as make it easier for you to troubleshoot in the future. Also, if it is the Blazer in your sig, move the rear lighting systems to the interior, instead of under the body. This will help with corrosion long term, as well as prevent anything from damaging the wiring while on the trails.

 

[StevoandaRedK5]

I've checked all the bulbs, and they are the correct types for each location. I can already tell you that some of the grounds are not good or intermittent. Now that I know that all the signals are routed through that turn signal switch, that will be what i check after checking grounds, and I probably have a good spare switch in my donor truck to swap in if needed.

Eventually I want to rewire the whole vehicle, but for now I will settle for it working within reason so I can be driving it.

 

[Russell]

Third vote for grounding issues!

Check the following grounding wires, and clean them up / crimp new eyelets on as required:

1. Passenger's side core support (near the battery)
2. Driver's side tail light (behind the reflector)
3. Dash harness ground (behind the dash bezel, just below the base of the A pillar)
4. Engine to cab (usually rear pass side intake bolt to the firewall itself)
5. Battery to core support (should be in the same spot as #1)
6. Engine to frame (usually up by the fuel pump)
7. Box to frame (usually under the center of the box just behind the bumper)

If any of those grounds are not there (even from the factory) add them in, you want to make sure every part of the truck that may have current passing through it has multiple clean paths back to the battery. If you've got lights that don't come on when they are supposed to, flash opposite of other lights, or come on dimly when they aren't supposed to be, that means that the device's ground path is blocked / poorly conducting so it finds other devices (usually another light) to ground through instead.