Unless your using the new style of solonoid switch, there should be no ground to it. The coil in the solonoid switch, gets its ground from the mounting bracket. Are you using the solonoid switch that has the terminals on either side, or the new one that has them all on the front? It has the two big terminals on either side, you dont have to ground it. When you bolt it to the car, that is your ground.
[addsig]