Fitting towbar electrics to a 1991 940SE estate

By tapping into the cables *upstream* (battery side) of the bulb failure detectors.

Roger,

Thanks for that.

Next silly question - where are these detectors located and what do they look like? Is there one per circuit?

Cheers

Peter

Don't know for sure, but

might offer a clue. This has wiring diagrams for 940's - but only for 1994/5 - but they are probably similar. It looks like there's only one unit, and that it's a circular can at one corner of the relay panel, behind the radio. (See the section on relay location etc.)

Groups 35 and 38 (further down the document) have more details of the wiring.

If my reading is correct, the only rear lights to be monitored are the brake lights. You would need to tap into the yellow and brown wire - after the brake light switch (3/9) but before the failure detector unit (7/75). You'll probably need to refer to the list of components (at the bottom of the contents list) in order to de-code the diagrams.

HTH!

When I installed mine, I didn't. I rarely tow a trailer so I just put up with the bulb failure warning coming on. If you tow regularly you can do as another poster suggested and tap in ahead of the failure sensor but that involves running the wires all the way up to the front of the car. Not an enormous task but you do have to pull a bunch of interior trim off.

Another possibility is to power the trailer brake lights via a relay. The small current drawn by the relay coil may not upset the bulb failure sensor (although there's no guarantee of that!). You would still, of course, have to run a 12v feed from the front of the car for the brakelights themselves - unless there's already a sufficiently heavy duty permanently live cable at the rear.