Power for the rear defogger in the 01 H6 is routed from the main fuse in the engine compartment fuse box to fuse #5 (20 Amps) and from there to the switching contacts in the rear defogger relay that’s mounted adjacent to the in-cabin fuse panel. When the defogger is turned on, the relay is activated, connecting the power from fuse #5 to the “FB-23” circuit going to the defogger grid.
On page 3 of the power supply routing diagrams, at the bottom, there’s a rectangle with FB-23 in it. That goes up to the defogger relay lower switched contact. The other switched contact goes to “I” on page 2, and from there to fuse #5 (disregard the “fuse #1” ID). Above the fuse, wiring goes to “B” on the first page, which connects there to the main fuse, alternator and battery. So the power goes from the battery, to fuse #5 in the main fuse box, then to the relay in the cabin, and on to the defogger.
Fuse #5 is powered all the time. I believe it’s a mini-fuse with test points on the top. The fuse could be problematic due to bad contacts or a partially failed fuse element. I’d probably replace it with a new on, and then check with the voltmeter and test light to see if the power there is good at both sides of the fuse.
So I’ve traced it all the way back to the relay that does click with the switch but doesn’t send power out to the wire that starts at the connector from the fuse box an goes to the rear window???
Have you removed and tested the relay, or simply replaced it with a new one to see what happens? Your description suggests that although the relay switching contacts might be “switching” (clicking), they could be worn or burned enough that little or no current can flow through the connection. That could lead to there being 12 V measured with a DMM at the output terminal of the relay, but when a test light or other current load is used to check for power, it doesn’t work, because the bad contacts are, in effect, a high resistance. (When there’s a high resistance, a good multimeter, with a high input resistance, could still measure the voltage because it doesn’t draw very much current; not the same as a typical test light that needs current to light up.)
