Hey guys... not proud of this one but here goes.

I was doing some re-wiring on my truck fuel pump harness this weekend. I may have also been enjoying too many cold ones while re-wiring. I may have not been paying that much attention to the wiring diagram... And I may have wired power to ground and ground to power by accident...

Anyways, now my PCM relay is clicking at the rate of a machine gun anytime I turn the key on, for some reason the left turn signal bulb is also illuminated. The only thing that fixes it is if I disconnect the tank selector switch. The fuel pump won't prime. I also checked the ground near the battery, it's good.

Am I cooked? PCM done for? Or possibly just fried the relay like a catfish? Anyway I can test it to see if it is ok? I appreciate the help! I'm adding "wiring" to my list of "shall not do while inebriated."

Here's a diagram for reference. Ignore the green circle. Truck is a 1997 F-350 5.8L CCLB 4x4 E4OD

 

FWIW, those relays go out quite often, I owned an '88 Range Rover that used the same relay for the fuel pump as it did for the ECU (LR's PCM). That was a Bosch unit though, as were the relays. I used to keep an extra in my box, and remarkably a friend of mine with an '87 Rangie had a no-start issue, and the relay fixed it. It is worth trying, as those relays are cheap. That was a common failure on the old Classic Rangies. I also own an '84 911, and Porsche used a similar Bosch unit. I had it outside during a rainstorm and water leaked in and soaked the driver's side, the ECU was flooded. A p-wrench friend of mine took it apart, cleaned it all out and dried everything, didn't replace anything. It's been in my car working for the past 20+ years.

 

Thanks! I'll try swapping a relay and see if that fixes it! Do you know a way to test to see if the pcm is good?

 

Unfortunately I don't. Have you tried disconnecting the negative terminal at the battery and waiting a few minutes? That will usually reset them, AFAIK.

I have a '97 F-SuperDuty, which is similar to yours, your truck should be made in Mexico? My F-SuperDuty is similar to an F-450.

 

if you have the EEC wiring diagram, you can connect power, ground, fuel pump relay, STI, CEL on the bench. After turning it on, fuel pump runs for 3 seconds then turns offf. Connect the STI and CEL and you should get blink codes.

theres a YouTube video of a guy that made a test box, works well, not 100%,

my guess is you’ve fried some wires, that are shorted together now, possibly damage to other components, relays, EEC, etc.

how long was power turned on when you reversed pos/neg?

 

would the EEC diode be worth checking? If someone doesnt know, the fusebox diode can be checked with a multimeter. a lot of multimeters have a diode checking function, but im pretty sure you should get continuity one direction but not the other , i could be wrong

 

You have a short
Melted together wiring somewhere
The problems are too unrelated to be anything but a short IMO
See if it will output codes is how you check your processor
It will output 11-10-11 if everything is "A" Okay
Never a bad idea to check the processor diode
If you reversed pos and neg at the battery with the key on, you will have fried a fuse link or two
Start there, pull on those yellow fuse link wires and see if any are elastic like a rubber band
Those will be the no good ones, with the burnt fuse link wire inside

 

I only supplied power while they were crossed for 5-10 seconds.

Thanks for the replies guys. I'll pull the multimeter out and start searching for a short today. Hopefully it's only that and I don't need a new PCM.

Been thinking more, in theory, shouldn't the relay have protected the PCM?

 

Truck is drawing 4.75 amps while not on. Definitely a significant short somewhere... will continue to update.

 

That much, i'd expect to see smoke or smell something burnt, yikes, that damn fermented water!

 

Foud it. Its somewhere on the instrument panel fuses. This one controls fuse 4, 8, 12, and 16 in the cab.

 

Fuse #8 seems to be the culprit. Seems like a lot of wiring to dig through 🙄🙄

 

I agree, and if the PCM is blown, you should see some wire or component fried on the board.

That and the @manicmechanic007 helped me in the past...

 

I have a draw (now managable) on the same fuse, but mine was never anywhere near yours, yikes.

 

Left turn signal bulb is staying permanently illuminated when key is on and fuse out... hmmm 🤔 going to trace and see where this goes.