Help!! Need Wiring Guru(s)

[JoelPry]

Hello all, I'm working on a Ram fire truck, at work, and I need some help. Can anyone tell me if there is a wire in the vicinity around/under the dash that either supplies a ground or + power when the vehicle is in park or neutral only? The truck is a 2001, with an automatic transmission. Any help would be appreciated.

 

[B.G. Smith]

Park or neutral

The park neutral switch is mounted on the drivers side of the transmission on the auto. The wire from the park/neutral switch is black with a white stripe and goes to the PCM and the PDC under the hood, the manual doesn't show it going into the cab. It is a single pole switch which shows to be open in the manual with other side of circuit going to ground when switch is closed. Hope this helps. bg

 

[illflem]

In order to get a positive in in P or N you will have to tap into the wire that BG speaks of and use it to trigger a relay. The only other place to pick up a hot in P/N is at the starter motor while cranking, don't think that's what you're looking for.

 

[JoelPry]

Thanks, I found the wire and used it as a ground, exactly what I needed. I appreciate it.

 

[docdyno]

Joel

Be careful here! In ECM circuits, a ground in not always a ground (so to speak). A number of sensors and switches ground through circuits in the ECM and are sometimes bussed together. If you add a parallel circuit to the PN switch ground and trigger it with a relay, make sure the relay switch leg has some sort of isolation resistor or diode. If you don't when the relay disengages an electrical "spike" can occur and can do nasty things to your ECM circuit as well as provide false data at times that may cause a drivability problem. Experience really is the best teacher. Oops!

Doc

 

[Motorhead]

Carefull!

Joel, If you are using this wire to trigger a relay to supply power to whatever you are trying to power up, Bosch makes relays with Diodes in them so that you don't get "back surges" when the relay is dis-engaged. When you break the power on a relay winding, they can send high voltage surges back into your circuits and can damage electronic devices.

 

[fest3er]

Re: Carefull!

Originally posted by Motorhead

Joel, If you are using this wire to trigger a relay to supply power to whatever you are trying to power up, Bosch makes relays with Diodes in them so that you don't get "back surges" when the relay is dis-engaged. When you break the power on a relay winding, they can send high voltage surges back into your circuits and can damage electronic devices.

Since one would want to isolate the new circuit from the PCM (at least *I* would probably want to), would it be reasonable to use a 2-pole relay to independently connect each lead (PCM and new equip) to ground when the neutral/park switch closes?



Fest3er