Hello All

Around 5 years ago my restoration on my 89 f250 came to a screeching halt due to fuse links burning up when I would attempt to start the truck.
Ive posted a few times over the years and members of the forum have tried very hard to help me, but the problem persisted and life would get in the way of my project.

Here is where I am at now

Literally every electrical connector is unplugged(even behind the dash!)
EXCEPT
the ignition switch
and the green plug pictured below

With the key in the ON position, it appears there is a short to ground with only the ignition switch and the green connector plugged in. Remember, EVERY single other connector is unplugged.

when I unplug the green plug, and only the ignition switch is plugged in, the short goes away. The multimeter does have a reading, but I believe it’s an acceptable number?

So at this point, the short has to be in the harness on the other side of the green plug going down to the transmission, right?

Nope, when I test all of the pins, they come back with a good reading!!

I know one of you knowledgeable guys or gals has the answer. Hopefully my explanation is decent enough to follow along.
I will be forever grateful to anyone who helps me see this through!

 

How about your grounds, do you have every single ground point connected? even the ones behind the dash?

 

I might be wrong, but the first circuit from ignition(RUN/START), is the EEC power relay. Is that relay functioning correctly?

 

I don’t right now, but I still shouldn’t be getting a short to ground in a fuse links power wire, right?

 

if the conductor can find an alternate path for the power because it is damaged.. would make sense to me?

 

Your yellow wire in the first pic, looks to have been spliced?

Is that not the main power feed to the underhood relay & fuse box on the drivers side inner fender?

 

What you are seeing is the fuse links

This power wire runs all the way to the big plug at the firewall.

 

This line does run power with the key on, back through the firewall to one of the boxes on the drivers fender.

It’s a brown box with a gray plug. There is a short to ground on one of the wires running to it also.

This is with ONLY the ignition switch and the green plug pictured earlier plugged in. The short goes away when the green plug is undone.

 

Additional update

I realized I had missed the oxygen sensor as I unplugged everything

I unplugged the oxygen sensor and my short is gone

Could my short be in the oxygen sensor itself??? Somehow the ground wire inside is connecting to the power?

 

Did you disconnect your battery when you were checking ohms?

 

I suppose the O2 sensor could be shorted.
Or, you have wires crossed on the O2 sensor.
Or, your computer is shorted out.

 

There is a big capacitor (Bronco 5.0 EFI here) over the ignition coil, I was told the thing was used to filter noise from the ignition to the stereo. The thing is, it failed with age, and when it happened, my truck starter burning the maxi-fuse that powers the fuel pump, leaving me stranded. I removed it and bypassed the connection, no more burnt fuses, and no noise either.

It might be a long shot, but it's worth a try.

 

i imagine a good condition coil, proper routing of wires, and high quality good wires with SOLID connections, as well as none touching eachother and no reason that EMI would be a problem between the other components for ignition, etc. its prob ok the capacitor was prob for aging ponents or just how confident they were back then on the cleanliness of the audio reception

 

The battery is not hooked up.

I went ahead and bought a new 02 sensor while I was in town. Plugged it in, and my short is back, so the problem is not the 02 sensor itself.

 

Pull your computer, check the inside. Don't replace it, just inspect it.