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

 

[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?

 

[DangerNoodle]

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

 

[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.

 

[73FJ40]

@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!