Brake light failure relay on 1992 245

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moon161@gmail.com - 17 Mar 2006 00:04 GMT

It looks like my brake light failure relay is broke- I step on the
brakes, the fail light goes on and 12V doesn't go to the brake lights .

First I thought no problem, I'll just do the dashboard dive and get to
the bottom off this. The brake pedal switch is good, and I decided to
bypass the relay after I saw that blue/red wire disapear into wire
harness and dashboard.

I tried bypassing the relay and using the brake pedal switch to feed
12V lights up the lights, but then I can't shift out of park since this
relay is actually the hidden nexus of all things volvo. Wiring the
relay right to 12V works if you want a couple brake lights on 24-7.
Not.

So I'm left finding the relay (relay 12 at D5 in the generic 240 wiring
diagram). Can anyone tell me where it is in dashboard land and how to
get there? I've got the sinking feeling that it's gonna be like a
heater motor- step 1: Pull the speedometer =8-0

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James Sweet - 17 Mar 2006 00:21 GMT

> It looks like my brake light failure relay is broke- I step on the
> brakes, the fail light goes on and 12V doesn't go to the brake lights .
[quoted text clipped - 14 lines]
> get there? I've got the sinking feeling that it's gonna be like a
> heater motor- step 1: Pull the speedometer =8-0

Relay? Or are you referring to the bulb failure sensor which is normally
a red cannister with a lot of wires going to it?

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moon161@gmail.com - 17 Mar 2006 00:35 GMT

Sounds right to me. Pictures I've seen of it look like a can. It's fed
by blue/red from the brake pedal sensor, and should output to the
instrument cluster, brake lites and the shifter interlock. Once found,
can pop it open and see if it's a relay inside or otherwise.

I looked in the console, and behind the radio, but haven't pulled the
speedometer yet. Sounds like I better change the wires over one by one
;0)

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James Sweet - 17 Mar 2006 01:57 GMT

> Sounds right to me. Pictures I've seen of it look like a can. It's fed
> by blue/red from the brake pedal sensor, and should output to the
[quoted text clipped - 4 lines]
> speedometer yet. Sounds like I better change the wires over one by one
> ;0)

The older ones have a number of glass reed relays, each has two coils
wound around it in opposite directions. These coils are in series with
the lamps, one on each side. When the load is equal (both lamps working)
the magnetic fields cancel out. When one lamp is working and the other
isn't, you have a field which activates the reed relay turning on the
dash indicator.

Newer ones I hear are electronic, I haven't opened one of them up yet.

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moon161@gmail.com - 17 Mar 2006 05:20 GMT

Cool. Do you know exactly what part of the dashboard forest to look in?
I've looked around the pedals & steering column, behind the radio, and
pulled the center console.

Thanks,

Andy

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