Electrical Gremlin

bobcowan · #1 (**permalink**) 06-21-2022, 04:46 PM

Never heard of this one before: When I step on the brake, the brake lights come on just like they're supposed to.

Unfortunately, the front parking lamps and the dash lights also come on. ???

I have replaced all of the exterior incandescent bulbs with LED's.

I have never noticed this before. Only after putting it back together after paint. And that's a simple plug in operation.

Tommy · #2 (**permalink**) 06-21-2022, 04:51 PM

Did you change anything to assure the LED bulbs have the correct polarity?

spdbrake · #3 (**permalink**) 06-21-2022, 06:44 PM

It sounds like you have the brake lights wired into the same circuit as your parking lights (which always come on at the 1st detent of the switch as does the dash lights).

If you've accidentally wired into the rear parking lights hot lead, thinking it was the ground for the brake light. It will backfeed what you are seeing occur. The brake lights will be getting its ground either thru the parking light or dash lights.

Or since the bulbs are twin contactor and if one of the socket connector base is twisted 90deg in the base the the brake could be running both circuits.

bobcowan · #4 (**permalink**) 06-22-2022, 06:50 AM

Thanx. I'll take the brake lights apart and see what I can find. When I took them apart for paint, I just unplugged them, and then plugged them back in to the same plugs. Didn't have to rewire anything. But I did take the bulbs out.

spdbrake · #5 (**permalink**) 06-22-2022, 10:38 AM

If you have the turn (single contactor) and brake (dual contactor) socket swapped it may cause that issue possibly. Or a single contactor bulb in the dual contactor socket.

bobcowan · #6 (**permalink**) 06-22-2022, 09:09 PM

Quote:

Originally Posted by spdbrake

If you have the turn (single contactor) and brake (dual contactor) socket swapped it may cause that issue possibly. Or a single contactor bulb in the dual contactor socket.

As soon as I get some time (Sat?) I'll check that out. Thanx.

Blas · #7 (**permalink**) 06-24-2022, 08:18 AM

Remove one bulb at a time and test. That narrows down the path to the problem.
Blas

twobjshelbys · #8 (**permalink**) 06-24-2022, 09:28 AM

Don't preclude that cable/sockets have been accidentally swapped. Disconnect everything and put one back at a time verifying correct operation of that piece before going to the next one.

BDR0572 · #9 (**permalink**) 06-27-2022, 04:35 PM

Usually when i have the feed back issue i have a grd wire some where not making contact and you could always add a diode if it is the LED feeding back .My 2 cents

bobcowan · #10 (**permalink**) 06-28-2022, 09:43 AM

I messed around with the rear tail lights last night. One of the bulbs was out. No big deal, easily replaced.

But, even with all four tail lights disconnected/unplugged, problem persists. Dash lights and front amber lights come on when the brake pedal is depressed.

Today I'm going to remove the front bulbs and see what happens.

bobcowan · #11 (**permalink**) 06-28-2022, 09:48 AM

Quote:

Originally Posted by twobjshelbys

Don't preclude that cable/sockets have been accidentally swapped. Disconnect everything and put one back at a time verifying correct operation of that piece before going to the next one.

Not possible. The two plugs are very different. 2 pole vs. 3 pole.

bobcowan · #12 (**permalink**) 06-28-2022, 05:45 PM

I removed the two front LED's. Same thing. Dash lights come on with the brake lights. Must be something under the dash. I studied the wiring diagram that came with the car. But it didn't provide me with any answers. I guess it's just something I have to live with.

spdbrake · #13 (**permalink**) 06-28-2022, 06:07 PM

Bob, It sounds like you may have direct short (chafe) between the those two circuits. If so then it would make sense that turning on your parking lights (ilum the dash lights as well) would also illuminate your brake lights (possibly dimly).

bobcowan · #14 (**permalink**) 06-29-2022, 08:42 AM

Quote:

Originally Posted by spdbrake

Bob, It sounds like you may have direct short (chafe) between the those two circuits. If so then it would make sense that turning on your parking lights (ilum the dash lights as well) would also illuminate your brake lights (possibly dimly).

I think you're on to something there.

The lower lights have an 1157 dual element bulb. Should be brake and running lights.

The upper lights are an 1156, single element bulb, for the turn signals.

With running lights on, there's no change when applying the brake. Same intensity. Turn signals work as designed. Problem persists with LED's, standard bulbs, and no bulbs.

Somewhere, the brake lights are activating the running lights. Weird. I'll have to take the dash apart and see if I can find the problem.

bobcowan · #15 (**permalink**) 07-12-2022, 05:10 PM

I've been kinda busy lately, haven't had a chance to work on the Cobra until today. I took a 15 minute drive up the freeway, parked for 30 minutes, and came home. When I came home, the problem had fixed itself. Great. Now I have to go in search of a problem that doesn't exist.

EricKeller · #16 (**permalink**) 07-13-2022, 05:36 AM

Quote:

Originally Posted by Tommy

Did you change anything to assure the LED bulbs have the correct polarity?

You've just answered to my problem - I have the same problem with LED when parking, but I am the person who indeed made some changes in bulbs' polarity. Oh, stupidly...
Thanks!

bobcowan · #17 (**permalink**) 07-13-2022, 09:03 AM

If the bulbs are built correctly, then I think it's nearly impossible to change the polarity. I can't think of any way to do that accidentally. You would have to take the connector apart.

BornWestUSA · #18 (**permalink**) 07-13-2022, 03:53 PM

It might be a loose/bad ground on the brake light circuit, find the ground points and verify no paint, corrosion or bad connections.

Do all your trouble shooting with known good standard bulbs in place, LED's can and often do start new never before seen problems.

Check the wiring to the brake light switch with the key on, engine off, is there power to one side of the switch?

bobcowan · #19 (**permalink**) 09-08-2022, 06:05 PM

I'm still struggling with this.

With engine ON, step on the brake pedal. Brake lights come on. But parking lights and dash lights also come on.

Turn signals work.

With the dash light switch, the parking lights, dash lights, and headlights come on, but not the brake lights.

I have unplugged all of the signal outlets from the harness, front and rear. No change.

I took the dash apart, looking for bad wires and connections - couldn't find any.

The brake pressure switch is mounted to the side of the master cylinder. There is one 20g red wire going in to the switch - power.
- if I disconnect that wire, no lights with the brake pedal

There are two wires coming out of the switch. A large red wire with no label.
- If I disconnect that wire, no change

And a smaller black/red wire labeled "Stop Lights"
- If I disconnect that wire, no lights with brake pedal

My thought is that there is a problem somewhere between the brake pressure switch and the dash. The supplied schematic is no help at all. All it shows is one wire from the pressure switch going directly to the brake lights.

My next plan is to disconnect the factory stop light wire, and run a new wire back to the outlets.

Any other thoughts?

spdbrake · #20 (**permalink**) 09-08-2022, 06:31 PM

In the beginning post you mentioned you had installed LED lights. Was the LED installation right after or during the reassy of the wiring upon return from the paint shop?

If so, one of the new LEDs may be shorting to the running lights side, and that will backfeed your dash lights and parking lights (aka running lights)

Do you still have the 1157 bulbs you removed to try?