Ok, I admit this isn't on a Ford, it's my old man's 1970 AMX, but it's an odd electrical problem we can't figure out. The front right blinker works fine when the headlights are OFF but when the headlights are on it doesn't blink. The other three work as they should. He has tried new bulbs, ohmed and voltage tested the sockets. Ohm reading was around 1-2ohms and voltage was 9v. The voltage also fluctuated when the blinker was on but when you put a bulb in it didn't blink. He has noted the bulb on the passenger side is brighter than the other side. He's trying to get it ready to take to Pigeon Forge next weekend for a car show and I 4.5 hours away. Does anyone have an idea of what could be going on??? Could a bad headlight switch cause this? Bad socket?
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The short answer is - bad ground. Probably for the lights in the right front corner. Tell him to back-probe the ground wire for the turn signal socket and measure voltage between it and the battery negative post (not just any "ground") with the headlights off and on and with the signal off and on. Report results.

You might also have a wire for the signal that's rotted out inside the insulation. It will show a no-load voltage, but, as soon as a real load like the bulb is placed on it, the voltage all gets dropped across the fault instead of the bulb.

Jumper across suspect ground circuits and see what happens. Repeat for the live circuits.

 

Can you elaborate on the jumping across the ground circuit? I'm not sure I fully understand.

 

Take a piece of wire, hook one end to the battery negative terminal, strip the other end to some bare copper, and then take the bulb assembly out or the lense off, put the signals on with the headlights so it's not working, and then take that bare copper end of the wire going to the neg of the battery and jamb it down beside the bulb so it touches the brass part of the bulb. I bet it starts working.

When it starts working, the light bulb will go off in your head as to what the problem is. Finding the problem is another story, it could be anywhere along the path from the brass part of the bulb all the way to wherever the ground in the harness is located.

 

Yes I would say it is a ground issue also.

The 70 AMX has the turn/park lights in the (plastic) grille, 70 Javelin in the steel bumper. There were also 2 different harnesses for each model so it is hard to pin point the grounds.


Because it is in plastic and IIRC the lights have 3 wires at the light - turn/park/ground.
I think that ground wire screws to the radiator support, you should have one on each side for each light. I also think the head light uses this same wire for it's ground IIRC.


I just checked my 70 Javelin and did not see any grounds to the support like I said above. All my wiring papers are packed away from our move and cant get to them at this time.


The park/turn & head lights grounds go into the harness with the rest of the wires and are taped up. Following the wires & harness from the light sockets across the radiator support back to fire wall the only ground I found was on the fire wall by the brake master/booster and has 3 or 4 wires in 1 eye let.

I would start at the bad light and do the test ground jumper to see if that will fix it. If so the ground wire at socket could be bad or wire going across the radiator support with the other wires might have broke but you may also want to try and clean that ground on the fire wall to see if that will fix it.
It is an easy wiring system so should be easy to fix.
Dave ----

 

Thank you guys for your advice. He has tried the jumper wire for an alternate ground but the light still does not blink and still burns brighter than the other side.

Dave, it seems like I remember the wiring was all wrapped up in electrical tape from the socket back through the radiator support, and possibly beyond?. I don't know if that is factory on those cars or not. I just sent him a screen shot of what you said. Poor man is frustrated because electrical is not his thing and I won't be there until Thursday night.

 

Look at the socket carefully and the pins on the bulb. One pin is higher than the other. Sometimes these old sockets wear out and the bulb can be put in backwards. That would explain why it's brighter when the marker lights are on.

 

He just emailed me and said he found the problem. The turn signal socket and housing are all one sealed unit on the AMX. He swapped them around and when he did the driver's side didn't work. So...it's a bad socket/housing. I told him conrgats. Now the hard part begins. Finding a replacement....hehehe

Thank you folks again for your advice and help!

 

I have been out of the AMC world a few years now but if he or you are not a member of The AMC Forum, American Motors Discussion Forums might want to join up as they should be able to help find anything either thru venders or members.
They also have posts on shows and swap meets you can pic up parts at.
I don't remember any one making new ones so it will be a good used one.
Dave ----

 

I have made/retro fitted universal sockets into original style light assemblies before. I cut the old socket out, used a file or step bit to get the hole the right size, and then used a universal socket like one of these.

 

I know he goes to some AMC forums, just don't know which ones. He said he posted the problem on a couple but no one apparently could understand the problem. You're right, there are no aftermarket ones available. We're going to the Spring Rod Run in TN this weekend. Maybe there will be one at the swap meet? Who knows...