Charlie

My wife's '89 740 GL has lost both its main brake lights. The light over
the trunk (back window) still works. Bulbs are good, contacts clean. No
voltage at the rear connectors when the brake pedal is pressed & the
back glass light is lit.

The owner's manual says that fuse #4 powers the brake lights, & pulling
it kills the back glass light.

Other posts talk about 'integrity relays' & repair of same. Could this
be my problem, & if so, where are they on the 740? I've followed the
bundle from the left tail light assy up to the seat back without finding
any connectors.

Thanks,

Charlie

Mike F

Charlie wrote:
>
> My wife's '89 740 GL has lost both its main brake lights. The light over
> the trunk (back window) still works. Bulbs are good, contacts clean. No
> voltage at the rear connectors when the brake pedal is pressed & the
> back glass light is lit.
>
> The owner's manual says that fuse #4 powers the brake lights, & pulling
> it kills the back glass light.
>
> Other posts talk about 'integrity relays' & repair of same. Could this
> be my problem, & if so, where are they on the 740? I've followed the
> bundle from the left tail light assy up to the seat back without finding
> any connectors.
>
> Thanks,
>
> Charlie

The bulb failure relay is the cylindrical relay in the central
electrical unit, just toward the front of the car from the fuses. The
terminal numbers for the brake lights are 54 (in from brake switch), and
54L and 54R outputs to the brake lights.

--
Mike F.
Thornhill (near Toronto), Ont.

Replace tt with t (twice!) and remove parentheses to email me directly.
(But I check the newsgroup more often than this email address.)

James Sweet

Mike F wrote:
> Charlie wrote:
>
>>My wife's '89 740 GL has lost both its main brake lights. The light over
>>the trunk (back window) still works. Bulbs are good, contacts clean. No
>>voltage at the rear connectors when the brake pedal is pressed & the
>>back glass light is lit.
>>
>>The owner's manual says that fuse #4 powers the brake lights, & pulling
>>it kills the back glass light.
>>
>>Other posts talk about 'integrity relays' & repair of same. Could this
>>be my problem, & if so, where are they on the 740? I've followed the
>>bundle from the left tail light assy up to the seat back without finding
>>any connectors.
>>
>>Thanks,
>>
>>Charlie
>
>
> The bulb failure relay is the cylindrical relay in the central
> electrical unit, just toward the front of the car from the fuses. The
> terminal numbers for the brake lights are 54 (in from brake switch), and
> 54L and 54R outputs to the brake lights.
>


And like the other relays, you can pop the cover open and you'll find
circuit boards inside, look carefully for cracks in the soldering, it's
the only failure I've ever seen on those.