I need a circuit to turn on and off a relay using a normally open momentary switch. I have to eliminate my ECM to regain overdrive control.

 

I can't tell what year of truck you have but might this help?

http://www.atsdiesel.com/additionali...02)%20v1.0.pdf

 

So i am thinking you need a latching relay. What type of output from the relay do you need, +12v i assume when on?

Check below at bottom of pg35

http://www.dlcparts.com/images/BoschGuide.pdf


Why the momentary switch? a toggle makes it much easier.

 

The truck in question is my 92. I want to use the existing OD switch to continue to perform the same function it is now, to turn off OD. I am going to use a pressure switch on the transmission to turn it on and the existing OD switch to over ride it when wanted.

 

There was a thread a couple years ago or so in the 3rd gen area that put a relay right at the exhaust brake switch in such a way that the ex. brake was turned on when the key was in the run position and turned off when you pressed the switch. Is this kind of what you want to do?