Hi, today I went to a car auction and was planning on buying a mint 2002 f350 Superduty. It was loaded and had 50,000 miles. I saw it the day before run perfect. Auction was tonight and went and checked it out again, went to start it and battery was dead... click click click click click........ Someone left the lights on. Anyway the lot guy comes over and hooks up the battery booster to the battery backwards. My friend tells him its on backwards and he says no Ive been a mechanic for 45 years thinks us 19 year olds are stupid. Well I came around from the back of the truck as soon as he turns the charger on and about 5 seconds later smoke starts coming from the alternator. We unplug it right away. The truck would now only run when the battery booster was turned on (hooked up right) it ran for 30 seconds and died (not enough juice). anyway, the batterys are so dead the key ringer wont even ring while the key is in the ignition with the door open. My question is What else can be wrong with this truck? Can it be just the alternator or ECU? etc??

 

Fried wiring harnesses, computer, alternator, and maybe more. It depends how much juice was pumped in the wrong direction.

 

I respectfully disagree, thats way more damage then would have been done.
If the truck ran after the backwards hookup, you will only be looking at the alternator. If you are mechanically inclined, it will probably only be the rectifier bridge inside the alternator, possibly the voltage regulator as well (also in the alternator). I would also check all fuses.

 

If the key was off when he hooked up the charger, then the PCM and FICM power relays should have had those modules shut off, so they should be OK. If they weren't, the truck wouldn't have run at all. The Keep Alive Memory circuit would have been active, so you might check it for KAM codes. Some other modules stay on all the time and they might be toast. So if you really wanted to buy it, I'd check all functions. Door locks, interior and exterior lights, radio, 4x4 if it's ESOF, etc.

The alternator is clearly shot and the batteries probably already were.