01 Expedition - Short in cruise control circuit and it isn't the pressure switch

[Dudeth]

As soon as the pressure switch on the master cylinder is connected it blows the 5 amp fuse associated with the windows/ interior lights/ and gear shifter interlock. The pressure switch is new and I can unplug the switch and put a wire in the harness that clips to the pressure switch and the fuse blows instantly exactly the same as when I connect it to the switch. Does anyone know of common places for a short on this circuit or have the associated wiring diagram? I drive a lot for work and really want that cruise control operational.

 

[stamp11127]

When you connect the switch back you are providing a path to ground for the electrical current. If the wire you add isn't going to ground then the problem is elsewhere.

 

[docraymund]

Time for wire tracing. Start from the actuator all the way to the fusebox and look for damaged insulation.

 

[Bedrck47]

What 5 amp fuse is blowing?

Could you give the location and fuse # of that fuse Post a picture if possible You can alo check your owners manual

 

[Dudeth]

It's fuse #15. I've read in some other places that this particular fuse isn't associated with the cruise/windows/interior lights/ shift interlock, but it most definitely is on my XLT. I'll do some tracing today if I have time. Does anyone have a circuit diagram?

 

[Bedrck47]

Which diagram do you want

 

[Bedrck47]

Fuse #15 5Amp is the power feed for the Generic Electronic Module (GEM), Brake Pedal Position (BPP) Switch


I would like for you to disconnect the connector that goes to the Brake Pedal Position Switch

Then install a new 5 amp fuse and see if it blows

 

[Dudeth]

Thanks for the feedback. The fuse only blows when I connect the master cylinder pressure switch or put a wire across the harness clip for the pressure switch. Everything works fine all the time otherwise and never blows a fuse. A circuit diagram for that 5 amp circuit might be helpful. So normally all of my windows, lights, shift interlock and everything is fine until I try to get my cruise control working and plug in the master cylinder pressure switch. So you're saying disconnect the brake pedal position switch and then connect the pressure switch and see if the fuse blow?

 

[Bedrck47]

Yes Sending you a PM check your in box

 

[Dudeth]

Done, many thanks!

 

[Dudeth]

I don't see a standard plunger type BPP switch. Is there a picture somewhere as to what it looks like on mine? My expy has the adjustable brake/gas pedals. I can't find a BPP switch for an 01 anywhere on the web for some reason. Is it built into the brake light switch? Also, didn't see anything about the brake pressure switch in those circuit diagrams.

 

[Bedrck47]

I will say this being I also have a 01 and have replaced the BPP switch is that it is a standard part carried by most auto parts stores My replacement was purchased from Advanced Auto
I also have the adjustable pedals

 

[Bedrck47]

Pictures

 

[Dudeth]

Ahhh ok, it's part of the brake light switch , got it.

 

[Dudeth]

I finally got time to check that switch today. I disconnected the brake switch, plugged in the master cylinder pressure switch and the fuse instantly blew. There must be some bare wire somewhere.

 

[stamp11127]

Switches (old style) just close a circuit so that current can flow. You have a "short to ground" on the branch circuit for the master cylinder switch. There isn't a load to restrict flow so the amps increase until it gets to the fuse rating.

 

[Dudeth]

That's what I figured from the beginning unfortunately. Now to trace that switch wiring.

 

[stamp11127]

Give me an email to send a diagram to...

 

[Dudeth]

Sent you a private message Stamp. Also, I had the expy confused with my explorer. The expy is actually a 2002, not 2001... whoops.

 

[Dudeth]

It seems the issue is the speed control servo. I checked out the wiring for the brake pressure switch and it's good. While checking I removed the speed control servo plug and found what seemed to be brake fluid in there and I could see where the plug and servo had been getting hot at pins 9 and 10. Pin 9 comes from the brake pressure switch and pin 10 goes to ground. I used some MAF cleaner on the plug and servo and checked the wire and pin 9 for a short to ground but found nothing. Apparently the liquid in there had shorted pins 9 and 10 and has apparently damaged the servo. I would have expected 9 to be shorted to ground inside the servo but that's not the case apparently. Now to try and locate a replacement servo. It seems to be hard to find for some reason.