94 940 brake light problem

The one in the fuse & relay tray is for front lights only The one for the rear lights (largeish relay like casing in grey) is against the side of the trunk near the aerial circuitry. You should get continuity through the unit. If not you need a new unit.

All the best, Peter.

It probably suffers the same burnt out shunts problem that some of the other solid state bulb sensors have, it's not too difficult to repair and a lot cheaper than replacing.

I may be wrong, but I believe all 940s (except the SE) have a cylindrical bulb failure sensor located in the most forward left position in the central electrical unit. The terminals with #54 on them are for the brake lights.

DTB,

Did all three stop working at the same time, or did you just notice that all three aren't working? Have seen lots of issues with lamps having corrosion issues with the contacts...not bulb to socket but the socket to the "bus" that feeds each tail light assembly. Usually it looks like a little black area either or both on the contacts of the socket contacts and/or on the bus that it makes contact with. For good measure I'd also clean and make sure the bulb is making good contact with the socket also.

I checked in the trunk and there is no sensor/relay there. The wire harness to the tail lights does go by the aerial circuitry but continues on unbroken towards the back seat where I lose sight of it.

Mike F: Excuse my ignorance but what is the central electrical unit you mention and where is it located? Is it where the fuses are located?

I am convinced that it is not the bulbs or corrosion and that I need to find that darn bulb malfunction sensor. Behind my fuse holder I have 4 "relays" that are black, gray, black and blue. Behind them are two larger (taller) units, one black and one white. Could any of these be what I am looking for?

If you remove the cover over the lighter socket, you will see two screws. When you remove them you can move the entire panel aside and gain access to the central electrical unit. The bulb integrity relay may be black instead of red but it is the only circular relay in the rack. The brake light terminals are marked 54R, 54L and the high light is a black wire with a yellow trace.

Bob