95 Volvo 850 Brake Light Problem

Thanks for any advice you can give me.
All the brake lights (both sides and high mount) have stopped working. The
fuse looks good and has been replaced as a precaution. Both bulbs have been
replaced. When I put a meter across the fuse connection, I see 12 volts
when the brake pedal is depressed, which makes me think the switch is OK.

Where to look next?

 

Well, Mike, if *none* of the lights are working and you've replaced
the bulbs, I would suspect the switch. You say the fuse has been
replaced so that should rule out that problem. I would be inclined to
pull the switch and check it with an ohm meter.

Chuck Fiedler
Nothing but Volvo since 1974
Currently a '93 240 and a '97 850

 

If you see voltage across the fuse, that's your problem. If you're
seeing voltage between each side and ground, then the fuse is OK.

After checking the switch on the brake pedal, see if there's voltage
(pedal depressed) at the bulb failure relay. It's located inside the
left frame rail inside the trunk. Look for power at the terminal marked
"54" which is the input for all 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.)

 

with the fuse inserted or without fuse?

If the fuse 11/12 is in, the pedal depressed and you can measure 12V, the fuse
is broken. Then after releasing the brake
pedal you should not be able to measure any voltage across the fuse except when
having a ground shortcut somewhere on the way between fuse and brake switch.

If the fuse is in and ok the voltage drop is practically zero and you should
never be able to measure a voltage across the fuse connections.

If the fuse is out the behaviour should be as with a broken fuse in.

Not being an expert, but after studying the wiring diagram for the five door
850, in
case you do not have access to the circuit diagram, maybe the circuit layout is
useful for you to solve the problem.

The circuit is:
battery plus - fuse 11/12 - braking switch 3/9 - branching point 23/201 -
connector 24/14 - in at connector 12 at bulb malfunction indicator 7/1 - 3 lines
(10,13,14) out from that to the rear left, rear right and high mount lights,
each of them then to ground. Since all 3 lights don´t work and if the fuse is
ok, the brake switch is declared not guilty, the problem should be after the
brake switch and most distant within the bulb malfunction indicator.

In my drawings the components are located in the 850 five door:
connector 24/14 left of the steering wheel (under the dashboard?)
7/1 bulb malfunction indicator somewhere left in the trunk (under the floor near
left back corner?)

in the sedan the 7/1 should be somewhere near the left rear light.

The brake light switch seems to be a simple mechanical switch somewhere near the
brake pedal.

To be taken with a grain of salt since I myself have not had to work on the
braking light circuit of my 850 yet.

Regards