1955 Thunderbird Front Signal Light Problem

[Florida_Phil]

I've got something weird going on with the front turn signal lights in my 1955 Thunderbird. My TBird was converted to 12 volts by a previous owner. I have had the car for five years and have never had electrical issues before this. The problem is when I put on the right turn signal, both front signal lights below the headlights flash. The left turn signal only flashes the left front signal light. Both tail lights work fine. Any ideas before I tear into this?

[Joe Johnston]

Since you:

"have had the car for five years and have never had electrical issues before this",

and unless you did some other work on the car, I suspect a failed ground connection. EASIEST way to check is to take a length of electrical wire, clamp it to the ground terminal of the batter, then strip some insulation and touch the bare wire to the outside edge of the bulb. Perhaps do it for both lights. Even better is to flatten a bit of the wires and jam a bit into the socket between the bulb and the socket. If the ground is indeed bad, you have quickly created an excellent grounding connection directly to the battery. While at it also check out the taillights in the same way too.

[ward 57]

It's never a bad idea to check the bulbs and sockets and apply di-electric grease. I'm thinking the wires should be traced to where they separate on the fender back to the switch for any chafed insulation. Why it only happens one way is a head scratcher.

[Florida_Phil]

I removed the clear plastic lens on the left front turn signal light and it started to work correctly. I thought I may have a bad bulb, but it looked good. I cleaned the wires where they go into the wiring block on the left fender well. Thinking it was a bad connection, I reinstalled the plastic lens. As soon as I put the three screws into the black metal lens retaining cover, it started blinking both sides on a right turn signal as before. I see there is a gasket of some kind behind the black metal retaining ring. Could the lens retaining screws be grounding the bulb? Weird?

[ICON 1956]

I would also clean the head screw and the threads.... Since you removed the lens...

[Florida_Phil]

I have traced the problem down to the screws holding the clear plastic lens in place. If I remove the three screws, the turn signal lights work as they are suppose to. As soon as I screw one or more of the three retaining screws in, both sides blink on a right turn signal. The only thing I can think of is I have a bad turn signal light fixture?

[55Greg&Amy]

Pull the bulb in the suspect socket and make sure the 2 contacts inside the socket aren’t touching. I’ve had this exact issue before and found that when the bulb was pushed in and turned the two contacts touched. To remedy this, I removed the bulb then slightly pulled the wires from the back and reinstalled the bulb then released the wires and everything was fixed.

[ward 57]

I may be out in left field but the problem shows up when you tighten the lense into the fixture as an additional ground. I'd check and clean the other fixture as the bumper may be grounding a short in the working fixture.

[paul2748]

It sounds like a typical bad ground. Make a a temporary ground (wire with clips on the ends) and attach one to the light housing and one to a bare metal spot on the body or frame. Check lights. If ok, then remove light, clean all surfaces including the screw holes in the fender (which usually grounds the housing) and reinstall. Make sure the innards for the bulb are clean as well as the metal part of the bulb.

[Florida_Phil]

Took both front turn signal light fixtures out of the car. On my bench, both bulbs, wiring and light sockets checked out good. Ran an extra ground wire with no change. Traced the wiring back to the fender block and discovered the left parking light wire had current on a right turn signal. Somewhere the right turn signal and the left parking light wire must be touching. Wasn't in the mood to crawl under the dash, so I left it for another day.

[ward 57]

Took both front turn signal light fixtures out of the car. On my bench, both bulbs, wiring and light sockets checked out good. Ran an extra ground wire with no change. Traced the wiring back to the fender block and discovered the left parking light wire had current on a right turn signal. Somewhere the right turn signal and the left parking light wire must be touching. Wasn't in the mood to crawl under the dash, so I left it for another day.

Sounds like you are whitling it down. Start at the block and work back. The most likely spots of cross wiring is at the body clips that hold the full harness down the fender and through the firewall. The insulation gets chafed through causing a short. Had that happened with my horn wire.

[Florida_Phil]

I removed both fixtures and found some frayed wires in the passenger side signal light harness. Ordered some parts. One thing I hadn't noticed before. The turn signal lights work with the turned key off. I never would have guessed that. Thanks for the feedback.

[ward 57]

Interesting. I wouldn't think they should work with the key off unless somebody decided to have constant power to use the turn signal as a hazard warning light.
Also get a can of liquid electrical tape. Available at any auto parts store. It's perfect for the end connectors where the insulation is cracked at the connectors. Clean and neat, seals and reinforces the connection. Kind of like shrink tube without disassembly.

[paul2748]

Ward is correct - the signal lights should not work with the ignition in the off position. They should work in both the accessory and on positions only.

I removed both fixtures and found some frayed wires in the passenger side signal light harness. Ordered some parts. One thing I hadn't noticed before. The turn signal lights work with the turned key off. I never would have guessed that. Thanks for the feedback.

[Florida_Phil]

Ward is correct - the signal lights should not work with the ignition in the off position. They should work in both the accessory and on positions only.

This car was converted from 6 to 12 volts by a previous owner. They left the ground positive. I reflashed the voltage regulator and switched the battery cables a few years ago. The car currently has a Casco alternator conversion. So far, this is the first electrical problem I have had in five years. After I fix the front signal lights, I will look into why the blinkers work with the key off. Possibly a bad Ignition switch?