'71: troubleshooting electrical problem / rear lights
Thread Starter
Instructor
Joined: Jul 2016
Posts: 111
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'71: troubleshooting electrical problem / rear lights
Neither my brake lights nor my back-up lights are functioning. It doesn't seem to be a problem with the bulbs or the fuses. Turn signals and hazard flashers all function correctly. Any ideas? This problem appeared suddenly, following some work I had done to the car. Thanks.
Le Mans Master
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From: Was New Orleans but swam to Baton Rouge LA
Cruise-In IX Veteran
Is the car an automatic or a manual? There are switches that operate those items. Brake lights are controlled by a switch on the brake pedal. The reverse lights on a manual are controlled by a switch on the transmission. They could be disconnected or have worn out and no longer making contact.
Team Owner
Joined: Sep 2006
Posts: 31,274
Likes: 4,366
From: Westminster Maryland
Hi 71,
Welcome!
First Post!
What part of the car was the work done on?
That might offer and indication of what the problem may be.
The brake light switch is under the dash and operated by the brake pedal arm.
The back-up light switch is mounted on the side of the transmission as sig indicated.
There are several grounds for the brake and back-up lights as part of the rear lighting harness… both at each light housing and the frame.
?
Regards,
Alan
Welcome!
First Post!
What part of the car was the work done on?
That might offer and indication of what the problem may be.
The brake light switch is under the dash and operated by the brake pedal arm.
The back-up light switch is mounted on the side of the transmission as sig indicated.
There are several grounds for the brake and back-up lights as part of the rear lighting harness… both at each light housing and the frame.
?
Regards,
Alan
Thread Starter
Instructor
Joined: Jul 2016
Posts: 111
Likes: 23
Thanks gentlemen. I took a quick look under the dash. Is the brake light switch the white cylindrical object? The car is in a dark garage with awkward access. When the sun comes out tomorrow I will take a better look -- particularly at the grounds as Alan mentioned. The car has a manual transmission. The work was mostly under the hood (new water pump, basic stuff like new belts and hoses) plus new exhaust and mufflers.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
If the turn signals and flashers work you can eliminate bulbs, wiring at the rear, sockets, grounds and anything else at the rear for the brake lights. That's probably the contacts in the turn signal switch, or the connector going to it. As said, the backup light switch is probably misadjusted, bad, or disconnected for that problem. The two shouldn't be related, but that depends on what "work you did". Get back to us on that and maybe we can tie the two together.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
Thanks gentlemen. I took a quick look under the dash. Is the brake light switch the white cylindrical object? The car is in a dark garage with awkward access. When the sun comes out tomorrow I will take a better look -- particularly at the grounds as Alan mentioned. The car has a manual transmission. The work was mostly under the hood (new water pump, basic stuff like new belts and hoses) plus new exhaust and mufflers.
For the reverse lamps, you may have broken a wire on the reverse lamp switch on the transmission when working on the exhaust. There should be a pink wire and a green wire going to it, and the connector is on the firewall by the master cylinder.
Last edited by 65GGvert; Jul 13, 2016 at 03:55 PM.
Thread Starter
Instructor
Joined: Jul 2016
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Okay, I appreciate the information. I pulled the plunger manually with no result. I'll save shorting the two wires for tomorrow.
For the reverse lamps, I spoke to the mechanic and he also adjusted the shift linkage. So now that I know where to look, maybe that will be an easy fix.
Fingers crossed on the brake lights. Given that the turn signals and hazards work properly, and that the spring on the switch works the plunger, if it is not the switch itself then I won't know what else to check.
For the reverse lamps, I spoke to the mechanic and he also adjusted the shift linkage. So now that I know where to look, maybe that will be an easy fix.
Fingers crossed on the brake lights. Given that the turn signals and hazards work properly, and that the spring on the switch works the plunger, if it is not the switch itself then I won't know what else to check.
Team Owner
Joined: Sep 2006
Posts: 31,274
Likes: 4,366
From: Westminster Maryland
Hi 71,
Here's the back-up light switch.
It's mounted on the driver's side of the transmission case.
The wire runs forward and up to a connector on the firewall just to the left of the engine.
The small rod runs rearward to the reverse lever on the transmission.
Regards,
Alan
The firewall connection.
Here's the back-up light switch.
It's mounted on the driver's side of the transmission case.
The wire runs forward and up to a connector on the firewall just to the left of the engine.
The small rod runs rearward to the reverse lever on the transmission.
Regards,
Alan
The firewall connection.
Last edited by Alan 71; Jul 13, 2016 at 06:12 PM.
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Drifting
Joined: Jan 2014
Posts: 1,866
Likes: 140
From: Sadieville Kentucky
Hi 71,
Welcome!
First Post!
What part of the car was the work done on?
That might offer and indication of what the problem may be.
The brake light switch is under the dash and operated by the brake pedal arm.
The back-up light switch is mounted on the side of the transmission as sig indicated.
There are several grounds for the brake and back-up lights as part of the rear lighting harness… both at each light housing and the frame.
?
Regards,
Alan
Welcome!
First Post!
What part of the car was the work done on?
That might offer and indication of what the problem may be.
The brake light switch is under the dash and operated by the brake pedal arm.
The back-up light switch is mounted on the side of the transmission as sig indicated.
There are several grounds for the brake and back-up lights as part of the rear lighting harness… both at each light housing and the frame.
?
Regards,
Alan
Wes
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
If you look at Alan's first picture, you can loosen those two screws with the slots and star washers slightly and adjust the rotation of the switch ***'y so it only connects when in reverse.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
If the brake light switch is not your problem, the next most likely is the contacts in the turn signal switch that pass the voltage through when not signalling, or the connector where the white wire feeds that voltage from the switch up to the turn signal connector.
Team Owner
Joined: Jul 2006
Posts: 22,190
Likes: 4,178
From: Kannapolis NC
Okay, I appreciate the information. I pulled the plunger manually with no result. I'll save shorting the two wires for tomorrow.
For the reverse lamps, I spoke to the mechanic and he also adjusted the shift linkage. So now that I know where to look, maybe that will be an easy fix.
Fingers crossed on the brake lights. Given that the turn signals and hazards work properly, and that the spring on the switch works the plunger, if it is not the switch itself then I won't know what else to check.
For the reverse lamps, I spoke to the mechanic and he also adjusted the shift linkage. So now that I know where to look, maybe that will be an easy fix.
Fingers crossed on the brake lights. Given that the turn signals and hazards work properly, and that the spring on the switch works the plunger, if it is not the switch itself then I won't know what else to check.
Thread Starter
Instructor
Joined: Jul 2016
Posts: 111
Likes: 23
Alan: As I've seen before, here and on another discussion board, your pictures are an incredible resource
65GGvert: thanks for the additional info. The mechanic suggested something about the turn signal as well.
I lost a day today to family time, which is never a bad thing. Will pick up on this tomorrow.
Thanks again.
65GGvert: thanks for the additional info. The mechanic suggested something about the turn signal as well.
I lost a day today to family time, which is never a bad thing. Will pick up on this tomorrow.
Thanks again.
Thread Starter
Instructor
Joined: Jul 2016
Posts: 111
Likes: 23
Update: Brake lights are fixed. First I got a new switch. Then I got under the dash, pulled the plug off the original switch but left the switch itself bolted in place behind the pedal. Then I plugged in the new switch to the loose plug wire and sure enough, the fiber optic system indicated that both brake lights were illuminated. I knew getting the old switch out and installing the new switch was not going to be fun, so as a last hope effort to avoiding that (and in a gesture toward keeping the car as original as possible) first I sprayed a q-tip with some electrical connection cleaner and used the q-tip to clean the prongs on the old switch (still installed). Then I plugged it back together and presto -- brake lights back in service.
Thanks for guiding me in the right direction. Probably a simple thing for guys who have worked on cars for years, but still very gratifying.
Thanks for guiding me in the right direction. Probably a simple thing for guys who have worked on cars for years, but still very gratifying.