I have a 1999 f350 7.3 and after it rains the truck goes crazy. The horn starts to sound off and I have to unplug it sometimes the truck key chime sounds without the key in it or the door not being open. the other thing is after driving the truck after it rains the truck will not turn off. The key is turned off and out but it continues to run. The only way I can turn it off is by pulling a fuse under the hood. Ford said that it sounds like an after market alarm system but I don't have one. can anyone tell me what to do to fix this crazy problem?

thanks

-John Rollins

 

welcome to the forum. wow, that beats all. gotta be the PCM??? computer's fried??? something is seriously shorted somewhere. need to run a AE diagnostics. try to find somewhere other than a Ford dealer if you want real help! good luck.

 

i'd look around for possible old wiring harness hack jobs from old alarms that may have been re-cut out...

or a possible wiring harness issue in general.

either way it def. sounds like ur getting water onto something that shouldnt be.. you might have a windshield leak thats getting water into teh inside of teh upper dash area.

 

Sounds alot like either a GEM or the PCM, the windshield been replaced recently? They as well as Clearance lights are known to leak down the firewall into the connections for the PCM and GEM.

 

Welcome to FTE.

I agree with Alan. The '99 MY is known for a leaky windshield. Look under the dash on the drivers side and look for signs of water leaking down the firewall.

 

X3 on the leaky windshield

 

Check your fuse box and see if there is corrosion there. Is the carpet ever wet or is there a moldy must smell in truck?

 

X 4 on the windshield. Somebody else here on the forums had that exact same problem and Im pretty sure he had a leaky windshield

 

X5...My boss had his windshild replaced and the truck went crazy, had it resealed and good to go.