If you have a 12V line shorting against the sled, and the sled is earthed, then the battery will go flat as all the blue smoke will leak out of the wires in the car. You probably wouldn't have much of a car left by now, either.

You are more likely to have a situation whee the sled is floating (ie. isolated in a plastic surround or some such?) and something is touching it above ground potential. If you see anything over a half volt, then I would be looking hard at your wiring.

It sounds as if you need to ground the sled. If your battery goes flat quickly, then there is a current leak along the earth wire, which you should be able to measure.