1970 Mercury Turn Signal Light Issue

[MarquisDropTop]

Hi. On my 1970 Mercury, the turn signals work with headlights off. When headlights on, one side doesn't blink and just glows when the turn signal lever is engaged. Bad bulb somewhere? Flasher issue? Thanks.

[rocketraider]

Do the parking lamps come on WITH the headlights? And do you have a factory wiring diagram for the car?

 

Try installing a new park/turn bulb first. If that doesn't correct it you may have to explore the parking lamp socket's grounding.

[Bloo]

I would start by looking for clobbered sockets in the trunk (can you tell I own a 70 Mercury? LOL).

 

Then check grounds for the signal bulbs, especially on the side that is screwing up, front and back. Also look at the signal bulbs on the bad side, front and back for a filament sagging and touching the other filament. If all that fails, look at the headlight ground wire on the bad side. I would expect it to not run very far from the sockets before it pops back out of the harness and screws to the body.

 

Welcome to the forum!

 

[MarquisDropTop]

Thank you! Here's the car in question. 

[Frank DuVal]

Classic ground failure on the rear side that is dim. That lamp is getting a “ground” through the other lamps since it is a dual filament lamp. This “ground” only works when the driving/parking light filament is not fed power from the headlamp switch. 

[MarquisDropTop]

So is it safe to say it's a rear bulb issue? Thanks. 

[rocketraider]

It could be either front or rear.

 

With head/parking lamps ON, look at each lamp individually. Park lights and tail lights.

 

Then operate the turn signal. If the lamp is operating correctly, it should be brighter than with only the running lights on. Whichever bulb is not brighter is where the problem is. Either a burned out filament or a grounding problem.

[MarquisDropTop]

Thank you!

[JACK M]

Get a test lead and make temporary grounds to the battery from all the odd places you can think of.

This sounds like a ground is bad somewhere.