Does anyone know where the pcm power relay is located is it in the engine compartment fuse box,also I keep blowing the 20amp fuse in the engine compartment fuse box that goes to the pcm power relay as soon as I turn on the ignition switch without turning the engine over. It's a 1995 F-150
Last edited by mtntop1; 05-05-2005 at 12:11 PM.
Reason: Forgot put year of truck
PCM power relay is the bottom right hand relay, fuel pump relay is above it. Fuse I feeds PCM relay and goes to a splice in the engine compartment that feeds all the sensors that control the PCM outouts - wire #361 red; Any short in this lead will blow fuse as will a burnt up relay. Pull the relay first and see if fuse blows if not put the relay back and disconnect PCM 60 pin connector at driver's side fender well below brake cyl/booster. make sure battery is disconnected while dicconnecting/connecting 60 pin connector to prevent damage to PCM and be sure the connector is moved far enough away from PCM to be sure it wont get pushed up and make contact while you try the power to the relays; there are also several feeds to the PCM thru the relay, only pin 1 goes straight to the PCM off Fuse I. Hope this helps - info from 95 elec/vacuum manual.
I traced the short to one of the wires in the Transmission ,It seem that when I changed the trans fluild a few months back I pinched a wire behind the filter.Looking at the wiring diagram power goes to the PCM relay and then branches of to the #1 and elect press control sol in the trans.So I dropped the pan and took out the filter and to my suprise the wire was pinched and the insulation was broken.Fixed the wire and put everything back together and the problem was gone.Thanks 95X15 for your input.
Glad you found the prob - did you just start having the prob after the filter change or did it take a while to show up? I wouldn't have suspected the transmission wiring to start with, did the wiring just get in the way when the filter went up? I'll watch thet a lot closer in the future. Thanks.
It happened a few months after I changed the trans fluild.When I put the new filter in and it push one of the wires up behind it and pinched it.I guess over time with any vibration the insulation on the wire separated just enough at the pinch point that it shorted out againist the trans or filter.As for suspecting the trans wires it showed in the elect.diagram that when the igintion switch is turn on that power from the pcm relay goes to a central piont and then branches off in five dierctions,two of whitch go to the trans so I started there first remebering that I had the pan down a few months before and got lucking.I'll be more careful in the future.