1988 k1500 Tail Light Problems

[philster3]

Hey all. I have a 1988 GMC k1500 in pretty good shape. It's been parked for a couple years while I was out of the country and now it has some kinks that need to be worked out.

Starting a couple days ago, the dir/stop lights are stuck in the on position, even when the truck is off and the key is out. The lights will function as intended with the directional switch is used, but not with the hazard switch. Additionally, when the truck is turned on, the reverse lights will turn on. They will stay on when the truck is shifted from park to drive to reverse and will intermittently turn themselves on and off, regardless of whether the truck is in drive or reverse.

My questions are: Are these two separate issues, or is it possible they are related? Does this sound like a shorted wire, or a faulty switch/relay. Everything with the front headlights and directional lights seem to be working fine.

I'm not great at truck maintenance and electrical systems isn't great so I'd love some help.

[rickpilgrim]

The brake light problem is likely the brake switch under the dashboard on the brake pedal.
Reverse lights sound like a switch also.

[Gauder the Goof]

Wonder how the circuit boards on the tails look?

[philster3]

The circuit boards on the tails look fine at first glance. I figure the problem is upstream of them anyway because the brake lights are staying on even with the key out. Something has to be messed up between the battery and the lights themselves because they are getting power. Right?

[68 TT]

Originally Posted by philster3

Hey all. I have a 1988 GMC k1500 in pretty good shape. It's been parked for a couple years while I was out of the country and now it has some kinks that need to be worked out.

Starting a couple days ago, the dir/stop lights are stuck in the on position, even when the truck is off and the key is out. The lights will function as intended with the directional switch is used, but not with the hazard switch. Additionally, when the truck is turned on, the reverse lights will turn on. They will stay on when the truck is shifted from park to drive to reverse and will intermittently turn themselves on and off, regardless of whether the truck is in drive or reverse.

My questions are: Are these two separate issues, or is it possible they are related? Does this sound like a shorted wire, or a faulty switch/relay. Everything with the front headlights and directional lights seem to be working fine.

I'm not great at truck maintenance and electrical systems isn't great so I'd love some help.

The turn signals & brake lights share the same wire back to the tail lights so it is possible the turn signal switch is defective and is causing all of your problems or it is a wiring issue at the base of the column where the turn signal and reverse light switch wiring come together.

[philster3]

Problem solved!

Well, two problems solved. When at rest, the brake switch interrupts the current flowing to the brake lights. Once the break is pressed, the current is no longer interrupted and the brake lights come on. In my case, the switch was off calibration and so the at rest pedal didn't interrupt the circuit. It's possible to easily readjust the switch so that it works again, but, I already a new brake switch, so I just replaced it.

As for the reverse lights, I pulled the neutral safety switch and found that part of the tab had broken off. As a result, sometimes the switch would catch and move when shifting, and sometimes it wouldn't. Put in a new safety switch and we're good to go!