Electrical Fire?!?

So it's a beautiful sunny day here in Maryland, temperatures in the high 60's on January 7th, which is historically unheard of. Anyway I decide to wax the jeep...

I get to the rear hatch and smell a distinct odor of electronics roasting. Soon after I realized that it was from the passenger-side rear quarter - exactly where I mounted the relay for the backup lights... So I ran and grabbed the hose and doused out what undercoating was already on fire, and then proceeded to snip off every wire on the relay. My question is, how would they have caught on fire? Water short? This was the first electrical mod that I did on the car, about 6 months ago. And I made sure that everything was OEM spec. Used a relay coming from the reverse signal wire, which then turned on the backup lights. Had a 10amp fuse between the constant 12v supply, and even turned the relay into a giant ball of silicone sealant so water wouldn't affect it. Anyone have any speculations?

maybe it overheated from all the silicone around it.

.... But why on a nice Monday morning at 9:30 am, when the last time my car was touched was the night before. Keep in mind the car was completely off, and had been so for the last 12+ hours.

They should only recieve power when the relay is tripped by the reverse lights. While I sprayed the fire out I noticed that they were flickering on and off.

DanMan2k06 said:

.... But why on a nice Monday morning at 9:30 am, when the last time my car was touched was the night before. Keep in mind the car was completely off, and had been so for the last 12+ hours.

They should only recieve power when the relay is tripped by the reverse lights. While I sprayed the fire out I noticed that they were flickering on and off.

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i dont know why, just trying to help.

i thought you said that the relay has a constant 12v? is it a constant 12v or a switched 12v when you start the jeep? hard to tell now, but maybe there was a splice or broken wire.

Well one thing is that if you installed reverse lights that were of a higher wattage than stock and powered them with the stock reverse light wire, you may have overheated the wire. My guess is there was a short in the relay as there would be no current flowing unless the relay were activated. Maybe this is how you did it but run a power wire of sufficient gauge from the battery to the supply terminal of the relay. Use the stock reverse light wire to trigger the relay. Make sure the trigger circuit of the relay has a good ground. This might get tricky because I found that the running lights are not grounded to chassis ground. I'm not sure if the reverse lights are. I hope this helps.

^ Yup did all of that, just as you said. And sorry 89 I wasn't getting an attitude. Here's another kicker - my stock reverse lights still work. I'm just pretty dazzled as to why my car spontantiously combusted.