All 3 brake lites are out suddenly. #4 fuse is good. Bulbs look good.

Any idea about a ground to inspect? (I keep all known grounds tidy). I suspect the switch at the pedal.

I may have this taken care of before anyone replies, but I would appreciate any input
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89 240 wagon, 94 940, 300K, 94 940, 141K

Known Good bulb out relay solved problem. What a revelation! Thanks to BB
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89 240 wagon, 94 940, 300K, 94 940, 141K

Now carefully pry the cover off the dead bulb out sensor with small screwdrivers and look at that pin that needs solder reflow. It's easy to repair for a good spare. Use 60/40 rosin core solder. (No acid)

Bill

Fuse 4
Check the brake peddle switch with a test light.
The bulb out sensor can go open and require resolder: pin 54S/9
940 or 945?
940 The ground is near the left tail light towards the center of the car.
945 The ground is next to the left taillight towards the fender.

Thanks BB
Bulb out lite on cluster works when the tail lite is out
Can bulb out sensor "go open" and cause no brake lites?
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89 240 wagon, 94 940, 300K, 94 940, 141K

Hi,

Yes, the bulb out sensor is in series with the brake lights and one failure mode
is to have the pins needing to be soldered. I gave you the number for the common pin from the brake switch that would kill all three brake lights.

Check the brake switch with a VOM or test lamp first.

Give your email and I'll send you the schematic.

Bill.

Can you tell me where to find the bulb out sensor? I have a couple spares that probably work
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89 240 wagon, 94 940, 300K, 94 940, 141K

The bulb out sensor is in the main fuse/relay block in back of your ashtray.
Check the part number as there are different bulb out sensors for different models.

Get the Volvo wiring diagram (Fault tracing,repairs & maintenance Greenbook)
The number you want for the 1994 940 is TP3904202
It has detailed schematics and also pictorial diagrams showing what the component looks like and it's location.
It's your best friend for DIY wiring issues.
Someone may have a valid link to find it on the web.

Good luck, Bill

Thanks, I knew I had seen it somewhere
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89 240 wagon, 94 940, 300K, 94 940, 141K

A classic bulb sensor relay failure -tall, round, red relay, leftmost socket in the back row of the relay tray in 700s/900s. Temporarily remove the neighbouring relay at the back for a better grip. The same bulb sensor is used in all later 700/900 models and later 240s. In your particular case with both sides of the brake lights out plus the third brake light, there will be no bulb out indicator warning light on the dash. All brake light circuits in the bulb sensor remain balanced left/right in this case, which is how it works.

If it's the Volvo style relay (not the KAE aftermarket) then the odds are 90% that cracking it open (pry the cover off around the base with a small slot screwdriver) and re-flowing the solder at the main conneections on the circuit boards will fix it as good as new. It's better if you add a bit of solder to act as an improved heat sink, but be careful that solder traces don't bridge to nearby traces and connections. It's not a job for a soldering gun, you want a fine tipped iron, at least 25W, preferably more.

In your case, with both brake light sides out, pay particular attention to re-flowing the solder on all the main solder points of the brake light circuit starting up from pin 54S (just plain 54 on some) and following the circuit board traces up the jumper connections to the upper board. One of the connections is slightly buried in the middle of the upper board, hence the need for a fine tipped iron. As I noted here recently, don't be tempted to straighten the fine sensor wires going through the sensor coils -the ceramic glass insulation is fragile and can fracture, ruining the relay.

While you're in there, might as well re-flow the other connections for the rest of the brake light circuits off main pins 54L & 54R and S (the 3rd brake light). Next most important (especially with DRL) are the headlight circuits off pins 56b, 56bL & 56bR. Park lights on the 57 and 58 pin circuits are less problematic. Be sure to do a final check with a magnifier under good lighting that there are no trace solder bridges between solder points that aren't also copper traced on the circuit boards.
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Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now