Repeated 15 amp fuse failure

Help needed from anybody who's been down Electrical Troubleshooting Expressway on the way to the nuthouse! My '89 5.0 Crown Vic keeps blowing the 15 amp fuse that oversees the
brake/four way flasher circuit. It seems to happen after a rainstorm or washing it in the driveway. Lens areas seem to be dry so I don't think water is getting into the housing. Ex police car with lots of aux "junk" and mods. (stripped off) so might be one for the shop? Thanks for any advice and experiences. Bob/Orlando
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Bob,
This might be a longshot... I'm an electrician, not an auto specialist.
A while back I was "helping" a friend troubleshoot a similar problem- the dreaded intermittant short. After a LOT of wasted effort we decided to do a really thorough procedure wherein we installed the fuse, and one-by-one activated the different systems of the vehicle. By systems, I refer to anything electrical, including fans, power windows, brake lights, flashers, turn signals, etc. You get the idea.
Anyway, the problem was actually traced to a dangling wire under the dash. Well... more likely under the windshield portion of the dash. I mean WAAAAAYYY up in the top of the underneath we found a wire that someone had previously cut and taped the end. After a while the tape fell off and the end was exposed. When we grounded the end, it sparked and blew the 20 amp fuse. Voila! The cause was found. We traced the wire to a junction where it had been spliced into this circuit and removed it. Never did figure out what the wire was added for.
How did we finally find it. We eliminated EVERY other system first, and then traced the entire remaining circuit wire by wire. Knew this was going to be a tough trace, so that's why we eliminated every other system first.
Now, none of this may help you in the slightest, but your problem just jogged this incident back into my memory.
Good luck, Gary Kasten
One more thought- Could the wiper arms be hitting something. You said when it rains or you wash the car. Sometimes we run the wipers a cycle or two when we wash our cars.
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Hi Bob, just wondering if you have a trailer plug on the back and if so check the connections. Regards John

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well could have had "blackout" installed. The installer will cut one of the wires going to the switch and install an extra two wires going to a remote switch to kill the brake lights. It could be that all the equipment was removed and you have a short to ground in this extra wire. If this was done to this car it will be obvious by the extra wires near the brake switch. Just cut them out and re-connect the originals.
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