Check out the service manual the black wire appears to go to the negative side of the battery.
You are correct and those same wires tie into the instruments etc. 12+ and -(dbankhotbusa @ Jun. 02 2007,00) That's something to consider. I have a time delay relay wired to mine. The white wire is (+) AND BLK /WHTwire is (-). Is this correct?
i had the same problem, but i put a switch on my hid.. but when i turned it on the gauges pegged out... so i took of the nose section and basically moved everything as far from the cluster as possible, the wires, ballast... not a problem since. i honestly think the current going throught the wires will effect the gauges.. just like the "radio noise" when you have rca's next to ground or power wire on a audio system.... and at my job a very smart engineer was doing some tuning to our flare and wires were running close to each other and it was giving us wrong readings, he noticed it, we moved them and no problems...