Do you have a (VOM)volt-ohm-meter ? Put your VOM on DC volts,and then turn on the rear de-fogger switch and then chk. for 12v at the wire that connects to the window grid.... if it is hot(12volts present) then switch off your de-fog switch and switch your VOM to Ohms. Put the two meter leads across the defogger grid itself. If meter shows some low resistance, then you know that the actual grid is Ok. So,if you have 12v., and a good grid, then the only thing left is the return path.. which is the ground. Check to make sure that that return wire has continuity to ground. BTW, Radio Shack has very inexpensive Digital VOM's starting at $10. I have a larger one in the shop and a small folding one that I keep in the car tool box. Tom