light failure sensor

jake1 · Post by **jake1** » 05 May 2003, 04:43

Where is the bulb sensor? I have tried to fix the dash light from coming on when turning on headlights. The lights all work fine but that light in the dash drives me crazy!
thanks

jake1 · Post by **jake1** » 05 May 2003, 04:45

forgot to mention in first post...it is a 90 740 GLE

Guest · Post by **Guest** » 05 May 2003, 11:20

Bulb failure sensor in a 90 740 is behind the fuse panel.

Take out the ash tray-it's behind there. You will also need to remove the EQ or the compartment right above the ash tray. If it's the compartment thing, take out the lighter and remove the plastic round trim cap that surrounds the lighter. There are two screws behind it. Remove these.

Slowly pull out the compartment, as there are wires attached to the back of it. Remove the wires from their blade connections, remembering what goes where.

The bulb failure relay is on the relay panel, behind the fuse panel. The relay is the round, coke-can lookin' thing in the back on the left. There's a good map of all this stuff at this link:

http://www.brickboard.com/FAQ/700-900/E ... yLocations

When removing it, I've found it's easier to sit in the passenger seat and use your left hand. More clearance that way. Just lift GENTLY and wiggle a little bit. There are 13 or 14 pins holding it in place, but it slides right out, and can only go back in one way (due to a plastic guide in the base), so don't worry about its position before removal.

If the relay is bad, you can try to resolder it (per the directions at the above-posted link), but this did not work for me. I just bought a used one over the internet ($20-a new one will run you about $65 aftermarket, $110+ at a dealer). The first one I bought didn't work, but the guy sent me two more, both of which did.

Good luck.

Guest · Post by **Guest** » 05 May 2003, 11:25

I may have waasted a bunch of time typing that last.

If all your lights work, and the dash light is still on, it is much more likely that you have an imbalance issue with your lights. For example, if you replace one tail light, and not the other, the sensor can go off because the two bulbs are slightly different. Thus, replace BOTH, whether it's tail, head lamp, etc. You may also want to check your license plate lights. Anyway, the problem might not be the sensor. Have you recently replaced any bulbs?

jake1 · Post by **jake1** » 06 May 2003, 04:44

thanks for the help. I did replace a brake light bulb when the sensor came on when braking. It ended that but now the sensor does not come on unless I turn on headlights. I have cleaned all bulb contacts as well as connectors.

Guest · Post by **Guest** » 06 May 2003, 14:17

Same is true for headlights. If you replace one, replace both, because if the two aren't matched perfectly, the sensor reads this as bad. The high beams are not governed by the bulb failure sensor, thus you'll probably note that the dash light goes off if you switch to high beams.

jake1 · Post by **jake1** » 06 May 2003, 18:53

Wish it would go out with high beams. Stays on with low and high.
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dpauto.com · Post by **dpauto.com** » 06 May 2003, 23:55

Jake, what you need to do is remove the tail light connectors in the trunk and apply some electrical grease to them. Then see if that helps.

Let me know or you can call me

Dave

billyar · Post by **billyar** » 07 May 2003, 18:53

thanks for the help. It is fixed. There was a US taillight bulb number and a European bulb number on the right side. They had the same wattage but the sensor sure noticed something!!

It pays to replace both bulbs as you said.

thanks again