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turn signal lights up tail light

weird problem is the rear turn signal crosses from turn/brake filament of bulb to the tail light filament. it's doing this on the left or right. when I turn on turn signal it crosses back n forth to the tail light. Anyone had or heard of this issue? where do I start to look? Do I have a short some where?


Staff member
Bad ground would be the first thing to check.


Staff member
or a bad bulb


Texas Chapter member
I've had all kinds of issues like that with bad grounds. Also had bad sockets cause issues like that.

I would start by checking grounds. I ended up adding numerous ground straps which cleared up some weirdness I was having.

Also check to be sure the wiring harness isn't pinched or damaged somewhere causing shorts.
My 77 F250 was just doing the same and was my signal light switch, so bought another, pulled the wheel changed it and works great, hope yours is an easier fix.


don't play well w others
Check for an old trailer wire hook up that is disintegrating, and shorting out

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