94 940 brake light problem

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dtb - 30 Oct 2005 20:37 GMT

All three brake lights on my '94 940 sedan do not work. So far I have
checked the brake light fuse and the brake switch and both are OK. I
get 12V on the yel/brn wire when the brake pedal is depressed. This
leads me to the bulb malfunction indicator. My wiring diagram says it
is located on the fuse block but I don't know exactly where it is or
what it looks like or how to access it. Any help would be appreciated.
I have to fix it to clear a police inspection ticket.

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Peter K L Milnes - 31 Oct 2005 01:42 GMT

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.

700/900/90 Register Keeper,
Volvo Owners Club (UK).

> All three brake lights on my '94 940 sedan do not work. So far I have
> checked the brake light fuse and the brake switch and both are OK. I
[quoted text clipped - 3 lines]
> what it looks like or how to access it. Any help would be appreciated.
> I have to fix it to clear a police inspection ticket.

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James Sweet - 31 Oct 2005 04:11 GMT

> 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.

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.

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Mike F - 31 Oct 2005 15:44 GMT

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.

Signature

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.)

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rndthought - 31 Oct 2005 17:22 GMT

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.

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dtb - 31 Oct 2005 19:32 GMT

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?

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User - 01 Nov 2005 02:10 GMT

> 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
[quoted text clipped - 9 lines]
> 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

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The goal when driving is to miss the maximum number of objects.

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