Need some help

[wheelman]

Ok guys and gals, it's been a while since I've been on here, but I need some technical help. Back in the day I asked about all the backlighting in my 97 going out, all guages are functional, everything works, but when I turn on the headlights, nothing lights inside the cabin, and the power driverseat will stop functioning. Now after much trial and error, I have found the problem...sort of. There is a short. The int. lighting is wired into the circuit for the license plate light, the power seat is on it's own deal. Either way, they are shorting out together, whenever one goes, the other usually goes. I replace the fuses, everyting works fine, but after driving down the street, they blow. I've tried everything while stationary to get them to blow, but they won't. They only short out when the car goes down the road (I am assuming they are rubbing against each other or some type of firewall or what not. HELP ME!!!! I love my boxster, she's my baby, and not having the back lighting is killing me, especially when driving at night (I do a lot of that). Has anyone come accross this before, or know engouh about the wiring to figure out where this is happening? Thanks in advance for any help.