Transmission Light Issue

[Jeff Papo]

The relay has 4 wires:

1. Ground (57T)
2. Ignition switched 24v to the relay coil (29T)
3. Switched 12v out to the TCM (290C 291C)
4. 12v in from the battery (290B 291B)

If you disconnect wire #3 and the TCM light DOES NOT go out then you have a wiring problem in the truck somewhere. Someone probably bypassed the relay and wired 12v power directly to the TCM.

If you disconnect wire #2 and the TCM light goes out then you have a wiring problem in the truck somewhere. That wire should only have 24v on it when the starter switch is set to "Run" so use a multimeter to check for that. You should also hear the relay click as you apply and remove power from wire #3.

There is a third test you can do to test for a bad relay that I will tell you later if you need it.

Augi

There is great info here! On my truck I have the same situation as above (2001 HMMWV M1123) when i disconnect #3 the light does not go out.
T29 24v in run only
537B 12.5v in run and 12.5v in off
537C 0v in off and 3v in on

also just found 657b on the actual light has 9v and seems to ground out as well

swapped out my relay unsuccessfully. installed a master battery off switch to avoid battery drain.

 

[Retiredwarhorses]

There is great info here! On my truck I have the same situation as above (2001 HMMWV M1123) when i disconnect #3 the light does not go out.
T29 24v in run only
537B 12.5v in run and 12.5v in off
537C 0v in off and 3v in on

swapped out my relay unsuccessfully. installed a master battery off switch to avoid battery drain.

if the trans lamp is on when engine off, ive had water filled TCM boxes cause this, as well as bad TCM.
my last one was an M1152 with a dim Trans lam, opened the box and it was soaking wet.
dried everything out and no more lamp Issues.

 

[Jeff Papo]

if the trans lamp is on when engine off, ive had water filled TCM boxes cause this, as well as bad TCM.
my last one was an M1152 with a dim Trans lam, opened the box and it was soaking wet.
dried everything out and no more lamp Issues.

great idea, I just checked this out and the insides are beautiful, clean , dry and looks new and unouched.

 

[ebs]

Thank you for all the input. Swapped out the relay and SUCCESS! Wasn't too awful expensive. Most importantly, it worked!

 

[jim1131]

The relay has 4 wires:

1. Ground (57T)
2. Ignition switched 24v to the relay coil (29T)
3. Switched 12v out to the TCM (290C 291C)
4. 12v in from the battery (290B 291B)

If you disconnect wire #3 and the TCM light DOES NOT go out then you have a wiring problem in the truck somewhere. Someone probably bypassed the relay and wired 12v power directly to the TCM.

If you disconnect wire #2 and the TCM light goes out then you have a wiring problem in the truck somewhere. That wire should only have 24v on it when the starter switch is set to "Run" so use a multimeter to check for that. You should also hear the relay click as you apply and remove power from wire #3.

There is a third test you can do to test for a bad relay that I will tell you later if you need it.

Augi

Hello, I have the same issue and replaced the relay and the trans light stays on. I disconnected number 3 and the TCM light stays on, I disconnected Number 2 and the light did not go out, how do I do the third test?, also all the gauge cluster wires are cut and butchered and thats probably why the light stays on