One more thing, at one time I had a wire that felt on the drive shaft, rubbing and grounded on the shaft. This caused the fuel relay to blow. Truck was still running but I had a current draw. Check those wires on the left side of the transmission going over the shaft then over the trany then to the soleinoid on the RH trans.

 

Sorry,
Had to do a bit of carpentry around the house.
The Sol. pin block is located on the passenger side of the trans. Also while you're checking the dryness and corrosion of the pins, check the first 6 to 8 inches on the wiring from the harness connector. Despite the heat shield being in place, I found the insulation on several of the wires to be completely corroded and/or burned off. R.A.

 

Hey dieselzen
In the zip under:

To check RPM sensor
1. Remove 2-wire connector end.

My wires go right into the top of the nut...there are no wire connectors there.

I posted pics in MyGallery...click MyTrucks and there are 3 pics showing the PC Modular boxes.The top right 20A is the one thats blowing.
The other pic shows the RPM Sensor and the connection.

 

Turbo Tuff,

You wrote:

"Just came in from the truck.I went to the Oil spout and off to the right there is a 1"nut with 2 wires coming out of it."

Yes, that is the RPM sensor.

"The wires are bared about 11/2" up the wire???"

The wires should NOT be bared. Sounds like a good place for a short.......

"Can I undo the nut and fix the wires?"

Yes, you can take a large size crescent wrench and loosen the hex head and it'll screw out. Looking at mine, I'm not sure how one would go about getting the connector out of the steel hex head body but to test it you really don't have to. You could hook the DVOM to either the bared wires you describe, or you could take a couple of pins, press the points through the insulation, into the copper wire, and get your readings off the pins.

R.A.

 

Ok,I got the RPM Sensor back on!!What a job!The wires would twist up even though I disconnected it at the Harness.
Anyway I did manage to get it back on and tested it.
When I reved the engine in park it rose so it's working.
I taped up the wires at the hex nut.
I also phoned around for a new one but the after market stores like UAP don't show it in their stock.Every other sensor like the VSS,but no RPM Sensor.Maybe a dealer part only??

I do have one more 20A but I'm going to do what Kidoo said and check the solenoid block pin first.

It sits on top and has plate in front of it so I'll remove it then pull the plug and check it.

Then I guess I should see if I blow that fuse!!

 

That is the RPM sensor. Should be a plug about 6" up the wire from the nut. Unplug that connector and unscrew the sensor. That wire goes straight to the tach on an IDI via the wiring harness. Look at that wire carefully around the alternator Injection pump area for shorts. After it gets past the alternator it should be in a harness that heads over to the passenger side fender well.

 

Well I checked the Sol Block connection and it was dry and in good shape.The seal was ok as well.

I put the new fuse in and this time when I turned the key it blew...never got a chance to start it.
???
I'm lost!

 

I'm assuming that the big black square fuses in the PC Mod box are the Main power supplies.

I don't have a manual so I don't have a Schematic of the wiring of the PC Mod circuits.
Somehow I need to find out what's all on the circuit that keeps blowing the 20A fuse!

I think I'll go to the back of the truck and make sure there are no bared or broken wires on my equalizer plug.

There's a short somewhere that's for sure.

 

Well I checked the Trailer plug wiring at the the back of the truck to see if there was a damaged wire but there wasn't.
I didn't have alot of time before it got dark so I'll be back at it in the morning.
I guess I'll try and chase the wire from the fuse thats blowing and see which circuit it goes to then what else is hooked into that circuit.
Sounds like alot of work but I don't have a choice.
If I was to bring the truck into a shop would they be able to tell me what the problem is by hooking into the PC.Mod with a code reader?

 

I'd remove the Fuse Box and check underneath it.

 

Ok...do you mean to just unscrew it and take a look at the wiring from that fuse?.

This is the box your referring to right?

https://www.ford-trucks.com/user_gal...=31902&width=0

 

Turbo Tuff,

I finally found a diagram of the fuse box you showed in your FTE picture.

Is the bad fuse the 20 amp located in the top, middle position of the fuse box in your picture (it looks kinda blown to me)? If not, then specify which one and I will tell you what it protects.

I'm going to try and get my scanner installed to scan the diagram I printed out of the Ford CD in the meantime. R.A.

 

Hi dieselzen...
Thanks for the pic!
Yes that 20A in the middle(at top) is the blown fuse!
There is one empty slot above that one that isn't used.
Yes the one marked "T" is the burnt one.

It shows a 30A in the pic,there is only a 20A in mine???
Should I change it to a 30A?
I've own the truck for 2 years and it's always been a 20A,I've never changed it.

Would the 30A maybe take the load?

Did you see the pick of the RPM(tach)Sensor?
That part is $82.00CAD...WOW!!
Can I just use liquid tape and seal them wires up?

 

Turbo Tuff,

So you're saying fuse block "T" is the one which keeps blowing? And as we now know, fuse "T" protects the "Trailer Electronic Brake Control Unit"(of which, I have no knowledge).

Despite the diagram showing a 30 amp fuse being used, you've got to remember this diagram is from a 1992 manual on CD so the circuit may have changed some. Plus, you say you've had the truck 2 years and this is the first time this fuse has blown.

I'd say you still have the underlying problem of what is causing the fuse to blow as you say there is no time delay between when you turn the key in the ignition and the fuse burning up. I notice the coolant reservoir and the windshield fluid reservoir are next to the box. Neither is leaking onto the fuse box, are they? Have you done some work on the brake area, or any electrical area, recently? How about snow and slush on the undercarriage? Backed into a snow drift?

Now that I know the circuit in question, I'll continue looking on the CD for a schematic.

Regarding the RPM sensor, no, I didn't see that pic. $82.00, even Canadian, is a rather large sum, and if the sensor is working there's no need to replace it......yet. Yeah, some liquid tape and some heatshrink tubing ought to seal that baby.

Will write later if I can find something more. If I were you, I'd buy a manual, even a cheap Chilton's, if it has an electrical section which will show a schematic of your year and engine type /w 4X4 option. R.A.

 

just bought a rpm sensor for my 92 f250 total came to $58.25 right from my local ford dealer.i belive it is a dealer only item.i agree with dieselzen just seal the wires up and should be ok.