Topic: Brake Lights Dim 3.5 volts


wlobb    -- 04-12-2025 @ 1:12 PM
  Hi guys, I've seen variants of this problem in other forums with mixed answers. Some make sense some are really out there.

My '51 Custom convertible brake lights have been driving me nuts. They work, but they are very dim. First, I thought I had the pigtail reversed--I did but even hooked up right and the brakes on the correct filament the brake light is very dim.

I put my voltmeter back at the pigtail and I'm getting 3.5-4 volts (6-volt positive ground system). I thought it might be the hydraulic switch, so I ran a jumper wire, and I have 6+ volts on the hot side of the switch. So, I started testing and I have 6 volts coming back out of the switch. There is a 1950 style FDT-14448-A junction that the turn signals and brake lights run into. I have six volts going into that.

Next stop is the turn signal switch--I just had the wheel off and the signal lights work fine--and I have the full six volts on the same green wire running to the back for the turn signals. The turn signal and brake lights look to share a wire. So, I know the wire is good. Somewhere between the FDT-14448-A junction and the taillights I'm losing 3 volts. Any comments or ideas would be greatly appreciated. I'm going a little nuts here...

Thanks, Bill


40 Coupe    -- 04-13-2025 @ 4:35 AM
  When you measured voltage at the lights where did you get the ground ? suggest measure to the best ground you can find ie: frame . You can have a poor ground at the lights with good polarity at the wires. Are the tail lights the correct brilliance?

This message was edited by 40 Coupe on 4-13-25 @ 4:40 AM


wlobb    -- 04-13-2025 @ 7:26 AM
  Hi, thanks for the reply. I removed the light housing and ran a wire brush with my drill around the bolt hole in the trunk until I had bare metal. I had a good ground, plus, I have 6.2 volts in the same wire when I just feed the wire from a power tap. Turn signal lights are bright and tail light is on the right filament in the bulb.

This one is a challenge…


JayChicago    -- 04-13-2025 @ 12:16 PM
  I think from what you have written you already know this: As you noted, the brake and signal share the same wire and filament from turn switch back. You have a bright turn light. So nothing wrong from turn switch back. Problem must be the brake power feed going into, or within, the switch.

Not familiar with the '51 wiring. I can only suggest you continue with your voltage tests at the brake circuit input to the switch, and perhaps within the switch if you can get in there.


wlobb    -- 04-13-2025 @ 2:34 PM
  Thank you for this! I found it. I have 6+volts to the block and 4 +/- at the green pin on the signal light switch. Something in the switch is taking the 2-3 volts. I'm ordering a new switch; it doesn't look there is a lot to do to fix it.

Part of me wants to get one of those column mounted aftermarket signals, the design of the horn and turn signal assembly is really tight and prone to problems, but I think my desire to keep my '51 the way God and Henry intended will win out.

Thank you, guys, for the comments.

Bill


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