Taillight always on

[MN73GMC]

I recently inherited a '73 GMC half-ton pickup, and one of the taillights is always on, draining the battery. I replaced the switch for the lights, and initially it appeared to have fixed the problem but now the same light is on, again. All other lights are functioning as expected. I'm not much good at electrical troubleshooting, but I can handle basic tests with a multimeter. Any idea where to start and what to look for? Thanks.

 

[AuroraGirl]

I recently inherited a '73 GMC half-ton pickup, and one of the taillights is always on, draining the battery. I replaced the switch for the lights, and initially it appeared to have fixed the problem but now the same light is on, again. All other lights are functioning as expected. I'm not much good at electrical troubleshooting, but I can handle basic tests with a multimeter. Any idea where to start and what to look for? Thanks.

sounds like a short to power or your brake switch is being held on possibly in some way. but it only does one? does pressing the pedal do both?

 

[MN73GMC]

Thanks. I did some testing as you suggested, and the other taillight is only lit when the lights are on - no brake light or turn signal. The taillight that is always on also feels oddly warm to me to the touch. It seems hotter than it should be.

 

[Matt69olds]

Disconnect the turn signal switch from the base of the steering column, see if the light goes out.

 

[Snoots]

GROUNDS!!! Clean them all.

 

[MN73GMC]

Well that is an interesting test - as suggested I disconnected the wire harness at the bottom of the steering column, and now both of the taillights go on and off as they should. The truck was my dad's, and my mom just mentioned to me that he recently had the steering column replaced - maybe that's related. So the fact that disconnecting that harness allowed the taillights to work correctly, what does exactly that indicate? Thanks everyone for all the advice. I'd happily clean all the grounds if I at all knew where they were.

 

[Matt69olds]

The hazard lights circuit is powered at all times, they are on the purple wire in the turn signal connector. It’s sounds as if that particular taillight is somehow getting power from the hazard circuit. Disconnecting the turn signal connector isolates the taillights from that power source.

That’s my theory.

Get a replacement switch, plug it in and see if the light works correctly. If so, it’s time to tear apart the column.

 

[MN73GMC]

Great, thanks. At least now the battery won't die on me and I can get the truck home next week where I can take my time with it. Thanks for the help.