I'm looking for wiring diagram info for troubleshooting a "no brake light" condition. 12V appears on both sides of fuse 4 - but not at the switch.

I have the Haynes '90 - '96 940 manual. It presents the '91 model year diagram only. That model year apparently is different from the other model years.

Any info on color codes, operation, and routing would be useful and appreciated.

Hi,

A "no brake light" condition can be caused by a bad bulb out relay. It is the relay that is round and orange.

Gus

when a $94 relay, created to detect a single rear bulb failure, can take out all three brake lights - without any indication? My only warning was from the police.

Hi,

I was trying to repair my cruise control and came across that information. Then I understood why people were tailgating me, they didn't know I was braking, because I had no brake lights. Volvo's are nice cars but they don't always do things right, like the flame trap.

Gus

"...created to detect a single rear bulb failure..."

Bob,

The Bulb Failure Sensor tests for equal current on each side of these three groups of lights (this includes 3 bulb brake lights):
Note that there will be NO warning light if ALL bulbs in a tested group are out.

• Tail lights
• Brake lights
• Headlight Low beams

Around '76 or '77 it even tested the license plate lights.


--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

I was a doubter before, but you are absolutely right about the relay. And the relay is easier to swap then the brake switch is to probe.

Thanks for throwing me a rope.

Voltage from F4 has to go thru connector C7 (Gn-Yel wire) before it gets to the pedal switch. From the switch it's Yel-Brn to the Bulb Out Sensor then out to each of the 3 lights.

Connector C7 is defined as being "at steering column, 8-pin".

--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thank you for the great detail.

I think I've found a connector with a hot at all times G/Y pin 8. The brake mounted switch that I'm looking at doesn't connect up with it. Color codes to the brake mounted sw. are O/B and W/B.

I've taken another look. I now see there is a second brake mounted switch closer to the pedal pivot. I've been troubleshooting the wrong circuit.

I have to put this down for now. I'll get back to you. You're the man!

"Color codes to the brake mounted sw. are O/B and W/B."

Sorry but that's the Cruise Control vacuum release switch.

Even sorrier to say I think the Brake Light switch is up higher.
--
Bruce Young, '93 940-NA (current), 240s (one V8), 140s, 122s, since '63.

Thank you for the detailed info, Bruce. You got me off the wrong path. And my (brake mounted) cruise control release switch works just fine (ha ha).

All I could see of the true brake switch was the plunger against the pedal. I wanted to test it so badly, but I couldn't easily get to it.

I'm happy to say that the bulb failure relay that I bought on ebay arrived yesterday. After cleaning the old relay pins, reseating it, swapping out and re-installing it it's clear that I've experienced a hard failure of the bulb relay. I had to see this to believe it.