My 89 740 has the switch for the rear fog light but I can't seem to get it to come on. Which bulb is it on the 740 and which relay controls it?
Ben

Well, then, this is interesting. Looking at my relay panel, I don't have the rear fog light relay. How hard is it to put that in? I assume, possibly wrongly, that the wiring is in place.
Also, my rear defroster doesn't work. The light in the switch comes on for the right time period so I think that the relay is working but no affect on the window. I don't have any wiring diagrams on this car so I don't know where to check for voltage at the back of the car.
Thanks
Ben

According to my wiring diagram, the rear window defroster has one black wire going to ground and a yellow hot wire from the relay. The yellow wire should have 12 volts on it when the relay is energized. On many defrost grids you can measure the voltage right on the grid itself. Try measuring the voltage from chassis to each side of the grid. One side should be 0 volts (ground) and the other 12v.

The rear fog lights are shown to be fed 12v through a grey wire from the rear fog light switch with no relay. Power comes through fuse #25. The diagram shows a fog light relat is used only for front fogs if the car has them.

Hope this helps.

They're the red lenses right under the rear running light, closest to the license plate. They're probably burnt out or vibrated/broken.

Rear fogs won't come on unless the main headlights are on and on low beam (stock wiring). There is also a foglight relay on the main relay panel under the radio/equalizer behind the fuses.