Trans Light on when the Run Switch is Off?

[DHumvee]

I have an 1157 from GP I'm slowly going through and noticed that my Trans light stays on when the switch is OFF. When I switch to RUN, the light gets brighter. Any ideas?
Thanks in Advance!

 

[Mogman]

That is an interesting thing that seems to happen often.
If you look at page 49 of the attached document you will see the trans. check light is only powered when the trans relay is closed, that is when the run switch is on.
I have not seen this personally so I have not had the opportunity to trouble shoot this.
I would be interested in what voltage is on pin U of the TCM and also what voltage is on wire 290/291 measured to ground with the run switch off.
There are two different 290/291s on each side of the transmission relay I am talking about the "switched" side of the relay.
Also step on the brake and see what the lamp does with the run switch off.

 

[86humv]

Relay will sometimes stick....with ignition off...go back to panel behind front right seat where relay is and pound on it...sometime relay will reset.

 

[DHumvee]

That is an interesting thing that seems to happen often.
If you look at page 49 of the attached document you will see the trans. check light is only powered when the trans relay is closed, that is when the run switch is on.
I have not seen this personally so I have not had the opportunity to trouble shoot this.
I would be interested in what voltage is on pin U of the TCM and also what voltage is on wire 290/291 measured to ground with the run switch off.

I am still in the process of tracing wires that GP cut with a grinding wheel.

That is an interesting thing that seems to happen often.
If you look at page 49 of the attached document you will see the trans. check light is only powered when the trans relay is closed, that is when the run switch is on.
I have not seen this personally so I have not had the opportunity to trouble shoot this.
I would be interested in what voltage is on pin U of the TCM and also what voltage is on wire 290/291 measured to ground with the run switch off.
There are two different 290/291s on each side of the transmission relay I am talking about the "switched" side of the relay.
Also step on the brake and see what the lamp does with the run switch off.

That's better than really bad news I suppose. We just moved from Fl. to Al. , my tools aren't here yet. As soon as I can get my hands on a voltage meter I will respond. My first truck took forever to be released, this one only took two weeks. I had to get it picked up from GP before the Al. move was a done deal. That means I got to ship it twice! Thanks for your reply Sir.

 

[DHumvee]

Relay will sometimes stick....with ignition off...go back to panel behind front right seat where relay is and pound on it...sometime relay will reset.

I know where the panel and red reset button is but what needs beating on?

 

[86humv]

I know where the panel and red reset button is but what needs beating on?

The panel close to relay bolts...about in the middle.

 

[DHumvee]

That is an interesting thing that seems to happen often.
If you look at page 49 of the attached document you will see the trans. check light is only powered when the trans relay is closed, that is when the run switch is on.
I have not seen this personally so I have not had the opportunity to trouble shoot this.
I would be interested in what voltage is on pin U of the TCM and also what voltage is on wire 290/291 measured to ground with the run switch off.
There are two different 290/291s on each side of the transmission relay I am talking about the "switched" side of the relay.
Also step on the brake and see what the lamp does with the run switch off.

The panel close to relay bolts...about in the middle.

The panel close to relay bolts...about in the middle.

The suspense was killing me so I opened the panel. What sticks? I want to thump it...

 

[DHumvee]

I am still in the process of tracing wires that GP cut with a grinding wheel.

That's better than really bad news I suppose. We just moved from Fl. to Al. , my tools aren't here yet. As soon as I can get my hands on a voltage meter I will respond. My first truck took forever to be released, this one only took two weeks. I had to get it picked up from GP before the Al. move was a done deal. That means I got to ship it twice! Thanks for your reply Sir.

Update: I found my meter... I haven't had time to find the two wires 290/291 yet but 687 A and B (the indicator TRANS light wires) are getting 8.7 v all the time making the dimmer light and 11.6v when the run switch is ON for the brighter light. Ideas??

 

[Mogman]

Both lamp wires are getting 8.7V as measured to ground?
EDIT and was that measured with the lamp plugged in?

 

[TOBASH]

Just out of curiosity, are any 24 Volt systems getting voltage? If so, the problem is in your EESS or PCB. If not, then it is most likely the 12 V solenoid (unless you have a short circuit somewhere bypassing the relay).

 

[86humv]

The suspense was killing me so I opened the panel. What sticks? I want to thump it...

View attachment 884923

relay is green

 

[DHumvee]

Both lamp wires are getting 8.7V as measured to ground?
EDIT and was that measured with the lamp plugged in?

No sir, I unplugged the lamp, put one lead in the female side and touched the male side. When I switched it to RUN the voltage increased.

 

[DHumvee]

Just out of curiosity, are any 24 Volt systems getting voltage? If so, the problem is in your EESS or PCB. If not, then it is most likely the 12 V solenoid (unless you have a short circuit somewhere bypassing the relay).

Everything is working but I have been chasing something that's making it run hot.

 

[TOBASH]

Everything is working but I have been chasing something that's making it run hot.

I should have been more specific. When the ignition is off, is there any 24Volt current flowing? If so, the PCB/EESS is sending power to the 12 V relay and the problem is the PCB not the 12V relay.

 

[Mogman]

OK, well that was not the information I was asking for, I'm sure you will get it figured out.

 

[Retiredwarhorses]

You guys need to break out the schematic, the transmission and it’s associated components are all 12v, The input voltage at the Trans relay from the ignition is 24v, once 24v is presented, the relay closes, this forces the adjacent 12v relay to close and supply power to the TCM and Transmission lamp, it’s a civilian 12v GM transmission setup, nothing fancy.

 

[DHumvee]

That is an interesting thing that seems to happen often.
If you look at page 49 of the attached document you will see the trans. check light is only powered when the trans relay is closed, that is when the run switch is on.
I have not seen this personally so I have not had the opportunity to trouble shoot this.
I would be interested in what voltage is on pin U of the TCM and also what voltage is on wire 290/291 measured to ground with the run switch off.
There are two different 290/291s on each side of the transmission relay I am talking about the "switched" side of the relay.
Also step on the brake and see what the lamp does with the run switch off.

Good Afternoon, I wanted to thank you for your response and help with my question about the trans light on my truck. I wasn't ignoring your advice, we were moving and I hadn't sat down in weeks long enough to figure out where those wires were located so I could check them. I am new to the hobby and eager to learn. Thanks again for your help.
I didn't know how to determine which was the switched side wires so I checked both.
- With the switch in the OFF position the top wire on the Reset button measured 12.6v and the bottom wire measured 0v. There is no change to the brightness of the trans light when you press the brake with or without the headlights lights turned on.
- The only time the light gets brighter is when you switch the Start Switch to the Run position (without starting it).
- The light goes OFF when the truck is running.

I look forward to hearing from you.
Dave

 

[DHumvee]

I should have been more specific. When the ignition is off, is there any 24Volt current flowing? If so, the PCB/EESS is sending power to the 12 V relay and the problem is the PCB not the 12V relay.

How would I tell if there's 24v flowing?

 

[TOBASH]

If you can turn on your lights when the ignition is off, or operate the flashers, then you know.

 

[DHumvee]

If you can turn on your lights when the ignition is off, or operate the flashers, then you know.

They are working fine. I just saw another owner asking the exact same question (same symptoms) on one of the Face Book groups. Must be pretty common, Thank you guys for the help.