Reverse lights stay on. Stumped. (1 Viewer)

JDS

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Jul 18, 2019
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53
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Saint Louis
I have a 1981 - 40.
100% original. No wiring changes.
I just noticed that my reverse lights stay on while the engine is running and while the key is forward in ACC mode.
Thinking it was the reverse switch, I bought a new spendy OEM switch and swapped it out. No change. Lights still on.
On the old factory switch I noticed a very slight wear through on the wire casing exposing wire. (See photo). Thought that could have shorted something?
Any ideas on what to test? What to look for?
Thanks!
JD

AC419361-47C8-46DF-A084-0D2DE7A34D1E.jpeg
 

JDS

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Jul 18, 2019
Messages
53
Location
Saint Louis
@JDS

I suspect you have a short between the two wires somewhere between the connectors to the switch and where the two wires join together on the branch to the switch.

You can prove this by disconnecting the switch and checking the voltage to ground from each of the two wires that connect to the switch. Based on your symptoms, both wires should have voltage.

I'm pretty sure that one wire to the switch is energized, and the other wire from the switch feeds power to the backup lamp when the switch is closed. Since your lamp is energized all the time, the two wires must be shorting somewhere they are in contact with each other, and that only occurs in the branch from the main rear harness to the switch.

I would remove the loom wrapping from those wires and look for the short, likely at some support or other place where they rub.

Good luck!
Thank you very much.
I am also suspecting a short. I’ve tried all the easy stuff.
I will report back with the solution I find.
My wife had an answer... pull the two bulbs!
She does not understand this stupid fj addiction...
Thanks for your timely and thoughtful response.
JD
 

Puget Hound

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Did you check the switch itself. Is it showing a normally closed contact?
I’m having the same problem on a 1974. I found the contact on the switch before and after installation to be normally closed.
 
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Sounds like you are getting 12V from other than the back-up switch--if you have the trans in neutral and the ignition sw on, and the backup lights come on-the b/u switch is bad or you are getting 12v backfed from somewhere else. as (73fj40 suggested) Are all the light switches off?
Try the hazard switch on with ignition off--any change in b/u lights?(could tell you if the harness short is connected to the different colored wire for that circuit)--same thing w/ the brakes.

Big t'shooting thing is what changed from before when the lights were working ok to now?--was anything done to the underside?(harness)--wash/cleaning/bulb changes/etc.--might direct you to the area that is the culprit.
Doubt it is a ground issue(although these are usually the issue with any electrical problem)--{That would be "Claudia's Admonition"---"It's a ground issue"}
The B/U lights get 12v from the sw--it normally only interrupts the 12v going to the lights until the switch closes--if you have disconnected the sw and still get lights on, it has to be coming from another 12v source-thus the check of the hazard sw or brake lights--if the bu lights don't do anything when you activate the haz or brakes, that tells you the feed must be coming from the primary light sw(headlights/parking)--You could hook up a meter to the bu light positive and start turning on each to see which one causes the voltage to spike(or just watch the light)---It won't tell you where--but it will tell you which wire(color) it is--pay attention to the main splitter connection that powers all those lights(mine was buried back in behind the rear bumper-jambed up in behind the rock shield--
 

JDS

Joined
Jul 18, 2019
Messages
53
Location
Saint Louis
Sounds like you are getting 12V from other than the back-up switch--if you have the trans in neutral and the ignition sw on, and the backup lights come on-the b/u switch is bad or you are getting 12v backfed from somewhere else. as (73fj40 suggested) Are all the light switches off?
Try the hazard switch on with ignition off--any change in b/u lights?(could tell you if the harness short is connected to the different colored wire for that circuit)--same thing w/ the brakes.

Big t'shooting thing is what changed from before when the lights were working ok to now?--was anything done to the underside?(harness)--wash/cleaning/bulb changes/etc.--might direct you to the area that is the culprit.
Doubt it is a ground issue(although these are usually the issue with any electrical problem)--{That would be "Claudia's Admonition"---"It's a ground issue"}
The B/U lights get 12v from the sw--it normally only interrupts the 12v going to the lights until the switch closes--if you have disconnected the sw and still get lights on, it has to be coming from another 12v source-thus the check of the hazard sw or brake lights--if the bu lights don't do anything when you activate the haz or brakes, that tells you the feed must be coming from the primary light sw(headlights/parking)--You could hook up a meter to the bu light positive and start turning on each to see which one causes the voltage to spike(or just watch the light)---It won't tell you where--but it will tell you which wire(color) it is--pay attention to the main splitter connection that powers all those lights(mine was buried back in behind the rear bumper-jambed up in behind the rock shield--
Thanks for your reply and all the other suggestions. You are exactly correct. The switch was fine. There was a short at the harness jammed up under the bumper. Back feeding power to both running lights. It was a strange problem that I gave way too much thought too! Just traced back the hot leads! But Very surprised that it did not blow a fuse! THANKS AGAIN!
JD
 

DangerNoodle

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Thanks for your reply and all the other suggestions. You are exactly correct. The switch was fine. There was a short at the harness jammed up under the bumper. Back feeding power to both running lights. It was a strange problem that I gave way too much thought too! Just traced back the hot leads! But Very surprised that it did not blow a fuse! THANKS AGAIN!
JD

Glad to hear! It's always nice to get wiring gremlins fixed. PITA to track down sometimes,
 

Puget Hound

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Thanks for the help with the wiring insight.
My problem seems mechanical instead of electrical. The back up light switch remains in the normally closed position when the transmission is in gear or not. When I removed the switch it returned to normally open.
I’ve taken the top off the transmission to find out why the switch is not opening. Now the fun begins.
Thanks again
Ray
 

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