Reverse lights stay on. Stumped. (1 Viewer)

[JDS]

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

 

[DangerNoodle]

Bad grounds cross-feeding through? Grounds can cause funny issues.

 

[JDS]

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

 

[Splangy]

Why not just test the switch with an ohmmeter?

 

[Pura Vida]

try putting it in first

 

[JDS]

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!

Why not just test the switch with an ohmmeter?

I tested old switch and it appeared ok. But I got inconsistent readings. Then saw the frayed wire insulation. Needed to replace it anyway with the fray so close to the switch.

 

[JDS]

try putting it in first

First through fourth! I had my wife run behind me to check...!

 

[Pura Vida]

First through fourth! I had my wife run behind me to check...!

haha sorry, I had to crack the joke , on a serious note, i'm not too sure about wiring, but I would check the sensor that sees if the car is in reverse or not, and play around with that sensor. It should probably be near the gearbox or something, then I would follow the wire to see if there is corrosion or anything, or check the fuse box..

 

[JDS]

haha sorry, I had to crack the joke , on a serious note, i'm not too sure about wiring, but I would check the sensor that sees if the car is in reverse or not, and play around with that sensor. It should probably be near the gearbox or something, then I would follow the wire to see if there is corrosion or anything, or check the fuse box..

Not aware of a sensor. I have the manual and checked the wiring diagram. I checked the fuse for that circuit. I’m not an electrician, but if the lights are, on they are getting juice...
I just thought somebody would know if it is a special circuit. Like s 3-way positive or something. Ignition and Gear actuated. It appears grounded via the switch threads.
??

 

[ceylonfj40nut]

Something to do with shifter shafts on top plate? Off by a detent?

 

[JDS]

Something to do with shifter shafts on top plate? Off by a detent?

Thanks for the response. I took the switch out of the case and grounded it. Depressed the roller ball and lights still remained on...
Next step is wire tracing.
Thanks!
JD

 

[JDS]

Bad grounds cross-feeding through? Grounds can cause funny issues.

Thanks for the response. I’m doing wire tracing now. Don’t know what I’m looking for. Corrosion or wear or MICE teeth marks. There was a nest under the hood when I pulled her out of a barn.
Just odd that the lights worked properly for two years and then I had the problem.
Thanks Again.
JD

 

[fjwagon]

Ohm out the switch, make sure it toggles. May be staying in the "on" position. Switches are usually a common to fail. Lubing and cleaning them help getting it to unstick. But you have to confirm the switch toggles on and off.

 

[JDS]

Ohm out the switch, make sure it toggles. May be staying in the "on" position. Switches are usually a common to fail. Lubing and cleaning them help getting it to unstick. But you have to confirm the switch toggles on and off.

Yes thanks. Good advice. The old switch was ‘swishy’ with fluid. But both new and old switches do not click when they toggle.
Is the switch supposed to have a click?
I am wondering if the circuit remains closed (lights on) with two positive wires, until the gear rod slides to open the circuit (lights off).
Seems to be the reverse of typical circuits.
Weird switch.
JD

 

[zerotreedelta]

Not sure on the '81, but I'm pretty sure my '76 is an open circuit that then gets closed by the switch when it goes into reverse. If you unplug the switch, do they go out?

This is from the '79 manual, but blue/Red is a feed from the fusebox, broken by the switch on the way to the rear, similar to my '76.

 

[pb4ugo]

IIR, on earlier models when the key is on power is supplied to the switch, when put in reverse the shift rail rod pushes on the switch plunger and then power is supplied to the lights. I would look in 2 places. 1. where the switch goes in the trans and see if something is making contact with the switch plunger all the time, and closing the switch. 2. look at the tail light grounds. At some point on later models Toyota added a ground wires to their tail light housings.

 

[JDS]

Not sure on the '81, but I'm pretty sure my '76 is an open circuit that then gets closed by the switch when it goes into reverse. If you unplug the switch, do they go out?

This is from the '79 manual, but blue/Red is a feed from the fusebox, broken by the switch on the way to the rear, similar to my '76.

View attachment 2633335

 

[JDS]

Thanks!
Yes. If I unplug the new switch the lights remain on.
If I plug in the switch, in and out of reverse, lights remain on.
If I depress the switch ( out of the gearbox with a good ground ) the lights remain on.
Power is getting to those damn lights independent of that switch!
That is my challenge!
I guess I’ve got to trace every inch of the wires with a meter...?

 

[zerotreedelta]

Very odd. If you put a meter on the switch's connectors with the switch out, I'm assuming you have 12v on both? (Only one should get the 12v feed)

The next easy point to check is the connector in the rear harness, back near the axle...unplug that and check if you're still getting 12v on the reverse light wire (red/lightblue most likely, but would need to confirm/find the right pin). That would at least start to isolate where in the harness the snafu is...firewall to connector, vs connector to rear. There's another connector up front for the rear harness, mine is on the passenger side of the firewall...that's the next easy point to troubleshoot from, it's a simple 8-pin type block as well.

 

[JDS]

Very odd. If you put a meter on the switch's connectors with the switch out, I'm assuming you have 12v on both? (Only one should get the 12v feed)

The next easy point to check is the connector in the rear harness, back near the axle...unplug that and check if you're still getting 12v on the reverse light wire (red/lightblue most likely, but would need to confirm/find the right pin). That would at least start to isolate where in the harness the snafu is...firewall to connector, vs connector to rear. There's another connector up front for the rear harness, mine is on the passenger side of the firewall...that's the next easy point to troubleshoot from, it's a simple 8-pin type block as well.

Thank you. Very helpful.I will get under there and start probing.