my friend at work has an 88 bonneville. his rear defogger doesnt work. fuse is good and filiments are all intact. he said someone told him there is a relay switch behind the glovebox that could be bad. any ideas ??

Make sure the connection to the window is OK. I think it attaches right at the window or somewhere around the rear deck.

There'll be one on each side: Power goes in the left side; the ground connection is on the right. See if current is reaching the rear grid, then work back from there. Wiring is in the trunk under the shelf.

Listen for the relay "click" when you turn the rear defrost off and on.

Agreed.

I don't know which would be more likely as I have had to repair both on various cars, but the timer-switch (with the relay) may have failed on you, or the connections at the back glass may have broken away.

See if you have current making it all the way back to the large cable (I _think_ it'* purple) connecting to the rear glass from the upper corner of the trunk.

If the cable is live when it'* supposed to be, take a _close_ look at its connection to the glass, and see if the solder has cracked apart. Also check the ground cable connection on the opposite end of the glass for the same thing. If either have broken away, the rear window may have to come out for repairs.

If the cable is dead, go back to the dash and check the switch and relay. On some models it'* all built into the defogger switch, which will have a large plastic body on it in back to hold all the circuitry. You may have to trace the fat wire from the rear glass to see where it goes up at the dashboard end.

Also check the fusebox to see if any large accessory cables plugged into it have been dislodged, since one of them may be the main power feed for the defogger.

check for power at the window.