Interesting headlight/turn signal issue

[llong66]

When I first brought my 85 M1008A1 home, the interior turn signal indicator bulbs were both bad. I had finally gotten around to replacing them and found an interesting issue. Everything works normal and as it should. When I turn on my headlights, the interior indicator for the left turn signal comes on steady. When I use my signals, it works as it should, maybe flashing slightly slower on the left side but other than that, all is fine. All of the exterior lights function as they should also. Recently I had reason to pull the instrument cluster out of the dash and noticed that on that particular bulb, the plastic over lay with the copper traces was not positioned quite right so I put it back as it should be and thought that might fix the issue....it didnt. Has anybody ever had or heard of anything like this? I have asked around several of the various parts places here in town and none of the guys there have a clue. Since everything functions as it should, its not a real safety issue or anything like that, just more of a curiosity. I would not even begin to know where to start looking for the cause of something like that. My flasher units were both replaced when I bought the truck, so I dont think it could be them.
Thanks for any help or insight!

Greg

 

[cpf240]

Bad ground(s) someplace. Check at each turn signal, headlights, all bulb sockets, dash ground point, etc.

 

[Skinny]

Install all new turn bulbs and clean all connections. Mine did the same thing...it's all about back feeding from bad bulbs or poor connections. Don't overlook your hazard switch either. That connection gets gummed up over time. Cycling it a few thousand times can make it better.

 

[markg]

look at the overflow bottle on the driver side, there is a ground for the left headlight under that bolt, also check the ground in the sockets for each turn signal. thanks. mark

 

[llong66]

Thanks much! I did not even have a clue where to start looking!!!

 

[MarcusOReallyus]

Grounds, grounds, grounds.

When grounds go bad, or partially bad, very weird things start happening.

So, when very weird things start happening, check your grounds.

 

[Warthog]

Yep, check for a bad ground on the radiator support. Also check the bulb sockets for he turn signals. The ground tab corrodes and breaks off.

Seem like this comes up every other month.

 

[ducer]

Check grounds, sockets and bulbs!!!!!!!!!!!!!

Denny

 

[llong66]

Man, are you guys on the ball!! I started piddling with this today, first place I checked was the ground at the overflow, in good shape, good continuity, so I moved on to my left front turn signal, sure enough the ground tab inside the socket was broken off! There was enough of it left I was able to bend it over and make contact with the bulb...problem solved!! Thank you all so much!!! Im just curious how, with no ground contact, it worked at all...I had noticed that bub was dimmer than the other and was going to change it, just had not gotten to it yet, now its nice and bright!

 

[Warthog]

It was using the rest of the circuit for it ground. You can get replacement sockets at the parts store. Under $10

 

[llong66]

Warthog, thanks for the heads up on replacement sockets! I am no electrical guru by any means, but I think I have a decent understanding of basic theory, etc. Im not sure I understand how it could have grounded through the two remaining contacts. Its my understanding that those two leads go back through either the head light circuit/switch or turn signal circuit/switch ultimately to the fuse block and the pos side of things, how does this lead to it being able to get back to ground?

 

[usmcpatriot]

I would go around the truck and file contacts and aluminum sandpaper anything else, then dielectric grease all grounds and contacts.