Tail lights don’t work until warmed up?

[67D100Pickup]

On my 67 D100, my taillights don’t work when it is cold until I have driven a mile or two, of course with the cabin heater blowing. I think they come on immediately if it is warm enough.

At first I thought the issue might be in the steering column turn signal switch area but I don’t know why the tail light circuit would be related to turn signals at all since turn signals alternate with brake lights, not tail lights.

This has been a bear to diagnose since they start working after a few minutes.

Any thoughts what might be doing this and how to correct it?

Jeff

[PwrWgnDrvr]

Maybe corrosion or crud on headlight switch terminals, connector, or internally. Do the front running lights do the same? If not, won't be the headlight switch. Also check firewall connectors for same.

[dodgeboykim]

On my 67 D100, my taillights don’t work when it is cold until I have driven a mile or two, of course with the cabin heater blowing. I think they come on immediately if it is warm enough.

At first I thought the issue might be in the steering column turn signal switch area but I don’t know why the tail light circuit would be related to turn signals at all since turn signals alternate with brake lights, not tail lights.

This has been a bear to diagnose since they start working after a few minutes.

Any thoughts what might be doing this and how to correct it?

Jeff

Tail Light/running lights do not go through turn signal switch. Only Brake/turn signals do.
Pull headlight switch and have a look at it.
Or its a bad connection in T Light circuit.

[nutz]

if you get a temp gun you will see the area that is failing will be warmer

[67D100Pickup]

Maybe corrosion or crud on headlight switch terminals, connector, or internally. Do the front running lights do the same? If not, won't be the headlight switch. Also check firewall connectors for same.

Front running lights work even when tail/tag lights don’t so the issue is clearly in the circuit after the split to front/rear wiring.

Dang this sounds simple after you guys talk this out :-)

Jeff

[67D100Pickup]

Maybe corrosion or crud on headlight switch terminals, connector, or internally. Do the front running lights do the same? If not, won't be the headlight switch. Also check firewall connectors for same.

Finally I had a chance to work on them when they were failing and confirmed that the problem was a loose firewall connector.

Good job PwrWgnDrvr. Thank you for that tip!

Jeff

[PwrWgnDrvr]