Had some serious frost on the rear window this morning and hit the button for the rear defrost and the light came on. About 3 or 4 minutes down the road I looked over and the light was off. Hit button again and it did not light up. Waited about 5 minutes more and hit it and it lit up. Ran for maybe 90 seconds to 2 minutes and shut off again. Waited another 5-6 minutes and turned it on again only to have it shut off in about 90 seconds to 2 minutes again. What controls the timing?

Check to see if there is any damage to the grid on the rear window.

I'm not 100% certain, but I think your car combines the timer and relay. You may have to change the relay. In my car it is in the fuse box under the rear seat, not in the fuse box in the engine bay.

Fuse box under the rear seat? Now that was better engineering huh? What if you dumped a Super Big Gulp in the back seat? I have a feeling my relay is under the hood near the wiper cowl. Owners manual doesn't show it in either of the inside fuse/relay boxes. Will check there this evening.

You may be right about it being in the box under the hood. I ckecked the 93 owner'* manual and it does not show up in either of the fuse boxes in the passenger compartment. If you locate it, exchange the relay (temporarily) with one of the others to see if that is the problem.

The relay is by the ECM located on the passenger side footwell, right of the glovebox. It'* a pain to get to.

On my 92 SSE, I have the same issue. I bet your power door locks do not work until the defogger relay resets.

I spent about 45 minutes last night reading both books of the service manuals and it appears that there is a timer relay located behind the A/C control in the dashboard. I did not find one labeled to control the defroster in either the under dash one or the one by the right side footwell. Didn't try the door locks while it was on becasue I didn't know it tied into that circuit. According to the service manual it should run 10 minutes the first time you push the button and then for 5 minutes the next time you push it unless you turn the car off, then it will reset to 10 minutes.