Electrical help - starts as soon as I connect the battery!

[fordjeep]

I'm definitely no mechanic, but I love my F250 because I can usually figure/fix it myself. I'm baffled. When plowing this year, I started having issues where the truck would die and the battery would crank for a few seconds and immediately die. Since the last time this happened & the alternator was actually smoking, I figured I'd just replace it. Well, I did and still having the same problem.

'When I have both terminals on the battery connected and the truck is just sitting, no ignition, no lights on - nothing - I can connect a voltmeter and watch the battery drain. When I disconnect the the terminals, the battery actually gains voltage. I connect them back up and the drain starts again. OK, a short somewhere is what I'm thinking - but how would I find it?

No, here is where it gets really weird. I took the battery out planning on returning it for a replacement as it's leaking anyways and is only 18 months old. For shits and giggles, I pulled the battery out of my wife's car to see if the same symptoms occur with a known good battery. Thank god I had it in neutral because as soon as I connected the second terminal the friggin' truck actually started. The key wasn't even in the ignition. So, I quickly realized I'm over my head and called my best bud, who's a mechanic and the first thing he said is "maybe I should just come up there tomorrow". He thinks my ignition switch might have gone bad or gotten fried in the process of me screwing around.

Anyone have any ideas? Thanks in advance.

[Wes]

The ignition switch is a good bet, also check your starter solenoid it could be stuck in the closed position. If the solenoid is closed it provides current to the starter and the ignition coil. This might be the source of your draw, with a weak batt you might only see the voltage drop and not crank.
Good luck

[seattle67]

I agree with Wes, starter solenoid is the first thing I would check.

[fordman]

it is a crossed wire some place. check the wiring under the dash going to the ignition switch and make sure it hasn't melted togehter . and around the solinoid.

[mr_josh]

Yeah, I'd guess when you look up under the dash, you're going to find the ignition switch harness has melted