1988 GMC Sierra Tail lights

KENNYG-M-C

MEMBER
1988 GMC SIERRA

Electrical problem
1988 GMC Sierra V8 Four Wheel Drive Automatic

I bought my truck a few years ago knowing I was going to have to fix a few things. The truck runs great but the tail lights dont always work. I can never get the reverse lights to come on, but the blinkers, break lights and tail lights work some times and not always all at the same time. It has the wedge type bulbs. I tried new bulbs first a while back - not the problem. On the driver side if I take the whole light fixture apart and reinstall it it'll work for a while then the blinker might work but not the tail light or he other way around. On the passenger side when I mess with the wire connections at the light or the connections by the trailer it works. Is there a replacement wire harness available just for the tail lights or maybe the whole exterior lighting?

1 Reply

CARADIODOC

MECHANIC
33,873 POSTS

Based on the age and the presence of a trailer harness, I'd start by looking at the splices where the trailer harness is connected. Electrical tape is a sign of trouble. Scotch-Lok connectors are quick but not suitable for use outside the truck because they don't seal out water. Soldered splices and heat-shrink tubing with sealant inside are the best choice. The car parts stores can supply the tubing with sealant.

If you do find corroded splices, it's important to cut the wire and insulation back far enough to find nice shiny copper. The dark brown, heavily oxidized wire will not take solder so you'll end up with similar problem in the future.

The next step is to flex the harnesses while watching the lights. If that has no efect, you'll need to find a test light or voltmeter, then we'll have to take some measurements. You're lucky that these are very straight forward, simple, reliable ciruits. There is no silly body computer involved as in newer vehicles.

Caradiodoc