Originally Posted by AcquaCow
You should also toss a ground wire from the battery to the firewall if you haven't already... best return path for the current...
Yes and to that effect, have you done the big 3? http://www.the12volt.com/installbay/...TID~73496~PN~1
Edit: just saw this was linked on the first page, but OP didn't respond. I would HIGHLY recommend doing this. We already know the engine grounds in scoobs aren't great.