Hello all...

This problem has me really baffled. First of all I purchased a used 01 F350 Supercab 4x4 with a 7.3. It's pretty basic. It has no power anything! Crank windows and you either push down the door lock button with your finger or use the key. So the electrical system isn't too complicated with a lot of bells and whistles. I'm tickled to have it, and I understood it needed some work. It had the bed swapped out and the previous genius cut the wiring loom when removing the old bed. Same for the new bed as well. I figured it to be a non issue and that I'll just trace everything back together and splice things back together. Needless to say I haven't reached this point yet.

Now here where it gets odd...


I check both batteries voltage and they are around 12.7 with the motor off. I fired up the motor and at the alternator or anywhere else I can tap a positive terminal I get 14.7. So the charging system is working.
I checked for voltage at the end of the rear main body loom at the tailgate. Nothing, no voltage. There is a large battery lead running to the back which is hot and not connected to anything. It's been isolated from ground as well as the ends of the main bed loom. I traced the OEM harness back to the three main plugs that lead into the fender well fuse block, no breaks or shorts that I can find. None of the fuses are blown relating to the rear lighting system. When I sit in the cab with the motor running and when I step on the brake the voltage drops on the dash voltmeter to the bottom of the gauge. When I remove my foot from the brake pedal the gauge jumps back up to operating voltage. I can do this all day long.....but I won't drive the truck until I can nail this bug.


So here is my question.....

Can the brake pedal switch short out internally and prevent current from flowing to fuse block and then the rear loom. If so why wouldn't a fuse blow somewhere in the system considering that the voltage is going into the crapper when I apply the brake? Then render the circuit inoperative. I'm by myself and it's hard to depress the pedal and take various voltage readings from different parts of the electrical system. It's a Big Truck!

I have a Chiltons manual and also have subscribed to a automotive data base, and they both are general in nature when it comes to schematics. They list relays and controls but don't explain the functions and operations of all. Some are self explanatory while others leave me scratching my head.

Any advise or suggestions would be appreciated. Also anyone have a good source for a OEM wiring harness/brake switch, just in case. : )

Thanks for hearing me out on this......

Art

 

someone told me when changing my fuel filter i could remove fuel from filter housing & fill with sea foam when installing new filter.this would help clean injectors & fuel system.is this safe to do?

 

Make sure you have a good ground at the rear. Run a long jumper wire to the neg on the battery and check your hots.

 

Make up a set of long leads so you can hook your meter up and take it to the cab so you can see what is happening. Verify that the voltage is droping from the batteries. If its doing as you said you will be letting the smoke out before long and then it will all quit working. Check to make sure none of the wiring igs grounded that should be hot because it would take a big load to drop your voltage that much. It would not take long for something to heat up and burn so be careful while testing. You would think it would blow a fuse before the voltage would drop much.

 

Talk to Ed at this link http://www.discountfordpartsaty2kford.com/I have ordered several times from him. His customer service is second to none and his prices are also the lowest i've seen on oem parts. Use the contact link and leave a message and he'll get back to you with the part you need

 

Ponch37300

Thanks for the tip! I'm a small fish in a new fish tank which is huge! If I need to replace stuff, which I'm sure I will, I'll contact Ed. Thanks a bunch!

Atrident, Aarkie

I would have never considered longer leads! Thanks for the tip! I'm used to motorcycles where everything is close by. Go figure!
I'll double check the ground out back as well. I did try grounding the voltmeter to the frame when testing current out of the rear loom's end. I was under the truck tracing and looking for power/hot leads.

Aarkie, roger that on the current load drop. I need to check what is actually going on at the battery when the pedal is pushed, and no, I don't plan on taking any smoke signal lessons either. : )

Thanks for your help guys, you given me some tips so I can do some more testing. That's always good!

Art

 

Ponch37300

I took your advice and gave Ed a ring. Everything you mentioned in your post was correct! I sourced a wiring harness for 500 bucks at a wrecking yard.
Disappointed with the quality of the 500 dollar part, I gave Ed a ring! In less than 15 minutes I had that harness and two more for my truck all for well under 300 clams!! Brand new!

Dude you saved me some serious bucks!
Thank you, Ed Olson, and of course, Ford Truck Enthusiasts!

Art