Weird light issue

[Bahn112]

Hi guys,

I just picked up a '70 LWB and i'm trying to get everything in order so I can drive the thing around.

I'm having a weird issue with my tail lights. Specifically my Drivers side tail light.
When the lights are off the brake light works perfect but as soon as I turn the running/headlight lights on and step on the brake pedal, it won't light up. The passenger side tail light works just fine.

Have any of you guys run into this problem?
Any suggestions?

[franken]

I'd pull the light assembly out and check the ground. In fact it isn't a bad idea to check/fix grounds all the way back to the battery, since they're usually sketchy.

[Bahn112]

Originally Posted by franken

I'd pull the light assembly out and check the ground. In fact it isn't a bad idea to check/fix grounds all the way back to the battery, since they're usually sketchy.

It's my understanding that the light housing itself is the ground so I cleaned up where the assembly bolts into the bed and that didn't do anything.
I thought it was weird that it works perfectly fine as long as the running/head lights weren't on. When the lights are on the parking light will work but as soon as the brake pedal is depressed there is nothing.

[franken]

K, funny symptoms say there's a ground issue.

[Bonestock3ott]

Is it possible that the wrong bulb was put in it or maybe someone forced the correct bulb in the wrong way and the brake filament is lighting as the parking light and when the much dimmer parking light filament lights as the brake light you can not see it.

[Bonestock3ott]

Another possibility is someone spliced a replacement socket pigtail and has the wires reversed

[Bahn112]

Originally Posted by Bonestock3ott

Is it possible that the wrong bulb was put in it or maybe someone forced the correct bulb in the wrong way and the brake filament is lighting as the parking light and when the much dimmer parking light filament lights as the brake light you can not see it.

I don't think this is the case as it works just fine as long as the parking light/headlights aren't on.
I did take it all apart and the I am ordering a new socket plug as the one that was currently on the truck looked a little hokey (definitely spliced a time or 2 by the PO).

Think it could be a bad headlight switch? Like it's routing the power incorrectly once the headlights/parking lights are turned on?

[Greenlee]

I second what others have said. Sounds like a ground issue. I had some weird issues like this after I replaced the wood on my step-side bed. After pulling my hair out trying to figure out what was wrong, I put a ground strap from the bed to the frame and my lights have worked fine ever since then! I guess the new wood somehow interfered with the ground.

[Bahn112]

Originally Posted by Greenlee

I second what others have said. Sounds like a ground issue. I had some weird issues like this after I replaced the wood on my step-side bed. After pulling my hair out trying to figure out what was wrong, I put a ground strap from the bed to the frame and my lights have worked fine ever since then! I guess the new wood somehow interfered with the ground.

I'm definitely going to get a ground strap kit. I've been reading up on them and they seem like an easy way to make sure that all the circuits have a good ground to run to.

Any suggestions on one kit over another?

[rpmerf]

Sounds like a ground. When the tail lights are off, the power goes from the brake switch, to the brake filament, then it should go to the ground, but since that isn't available, it goes back through the running light filament and grounds through the headlight switch.

When you initially turn on running lights, the running lights are grounding through the brake pedal switch.

When both are providing power, there is no ground available, and the light turns off.

I'd be willing to bet the driver's side tail light is brighter than the passenger's light.

[Bahn112]

Originally Posted by rpmerf

Sounds like a ground. When the tail lights are off, the power goes from the brake switch, to the brake filament, then it should go to the ground, but since that isn't available, it goes back through the running light filament and grounds through the headlight switch.

When you initially turn on running lights, the running lights are grounding through the brake pedal switch.

When both are providing power, there is no ground available, and the light turns off.

I'd be willing to bet the driver's side tail light is brighter than the passenger's light.

In addition to getting some grounding straps, where are the ground locations for the taillights? I want to clean them all up back there to ensure as good a ground as possible.

[rpmerf]

I think it grounds where the backing plate bolts into the body