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Deleting Bulb Failure Circuits

M

Mylesofsmyles

A Member
Joined
Jan 18, 2010
Looks like the only thing dependent on the system is the rear, center brake light...which my car lacks anyway.

I've got my harness open, and I'm eliminating all that I don't need.

Anyone eliminate this before? Just want to be sure, before I go unpinning connectors.

The leads from the bulb failure relay to each individual light is just a "tester" to check for a complete circuit...the bulb triggers are separate, no?
 
Is your bulb failure light on ? on the dash ? . I can never get mine to come on( it normally is on in key position #2 ) even if I take a bulb off one side .I heard from IPD that the system compares left side power draw from right side power draw . ?? not so sure if it works that way. Took a bulb out one side . still no bulb out warning on the dash .. But when I a front signal bulb was really out, then my dash arrows where flashing twice as fast maybe 2,4 times as fast ?:dance:
 
Mylesofsmyles said:
Looks like the only thing dependent on the system is the rear, center brake light...which my car lacks anyway.

I've got my harness open, and I'm eliminating all that I don't need.

Anyone eliminate this before? Just want to be sure, before I go unpinning connectors.

The leads from the bulb failure relay to each individual light is just a "tester" to check for a complete circuit...the bulb triggers are separate, no?
Click to expand...

I do know that in the case of the headlamps, they actually feed through the bulb failure sensor. When it's removed, no headlamps.

If the warning light keeps coming on when you hit the brakes, try swapping in a black sensor instead of the red one that's likely installed.

What you might want to do is look at a 1973 140 or 1973 164 repair manual and go through the wiring diagram to see where the wiring goes to on the lights. That was the only year and models of Volvo that had the modern(ish) dash without a bulb failure sensor.

-J
 
The sensor is part of the circuits, so no sensor means power to any bulbs wired through it.

What I've been thinking about doing for years (but I'm hopelessly lazy) is to hack up a spare sensor and solder jumper wires across the appropriate pins. A simple wiring diagram is all you need.

-Ryan
 
Hmm, I think this could be the source of my taillight woes. I have a permanently lit bulb failure light, all lights work except my stop and back up lights, which are intermittently non-working. Im interested to see how you get on with this, Im going to do some investigation with a multimeter tonight.
 
Yeah...re-read the diagram...pretty critical as wired.

I'll leave it; it's caused no issues, just going minimalist.
 
i cut out and bypassed the red coke can thing on my 244 years ago, it kept being a headache when finding lights that didn't work
 
I hate this sensor too.

The below diagram is for an '81 240.

If this sensor is needed in the loop, then what circuits are bypassed to eliminate it?
Do we simply connect the light pins to the fuse 15 & 16 pins and call it a day?
Dave B
 

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  • bulbfailsensor.jpg
    bulbfailsensor.jpg
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The damn thing has been coming on with the brakes for years on my wagon, since I installed the wing with an LED brake light. If there's some way to kill just that circuit I'd be MUCH happier!
 
dbarton said:
I hate this sensor too.
If this sensor is needed in the loop, then what circuits are bypassed to eliminate it?
Do we simply connect the light pins to the fuse 15 & 16 pins and call it a day?
Dave B
Click to expand...

Thanks for the image! Ideally, you'd jumper all of the pins to the appropriate pin(s) with the obvious exception of the one that connects the idiot light to ground.

Every circuit that it "senses" is needed for those bulbs to work: Headlamps, tail lamps, brake lamps, etc.

-Ryan
 
Ryan_R said:
Thanks for the image! Ideally, you'd jumper all of the pins to the appropriate pin(s) with the obvious exception of the one that connects the idiot light to ground.

Every circuit that it "senses" is needed for those bulbs to work: Headlamps, tail lamps, brake lamps, etc.

-Ryan
Click to expand...


?????
Ideally, you'd jumper all of the pins to the appropriate pin(s)
Click to expand...

Can you provide an example? I don't see any obviously "appropriate" pins.
 
Connect
2,6, and 7 Low beams
3,4, and 5
9, 10, and 11 Brake lights
12, and 14 Right side park and tail lights
13, and 15 Left side park and tail lights

Pin 1 is power from the bulb out light, when the reed switch closes it grounds the bulb out light through pin 8, turning the light on.
 
Last edited:
Dave,

Look at the diagram again. See where there are terminals connected with squiggly lines to signify resistors? Hook those terminals together, and the car will become a 1973 model.

-J
 
Actually those are coils of wire not resistors.

What's happening in the sensor? Current for lights on one side of the car flow through a coil of wire. Anytime DC current flows through a coil it produces a magnetic field.

The contacts inside the bulb in the center of the relay are closed by magnetism, this is a reed relay.

In the bulb failure relay there is a coil for the left side lights, and a coil for the right side lights. They are wound opposite of each other, one coil is wound CW while the other coil is wound CCW.

When equal current flows through the coils they cancel out each others magnetic field, and the contacts in the reed relay remain open. If the current between left and right is not balanced (the same) then the reed relay is closed.

The volvo relay is separated into sections, one for low beam headlights, one for park and tail lights, one for brake lights, and one for turn signals.

Any current imbalance in any section will close the reed relay which completes the bulb failure light circuit.

The newer bulb failure relays are electronic.
 
You know entirely too much about that sensor. I suspect you're not human, but actually an interactive computer program.

vlvman said:
Actually those are coils of wire not resistors.

What's happening in the sensor? Current for lights on one side of the car flow through a coil of wire. Anytime DC current flows through a coil it produces a magnetic field.

The contacts inside the bulb in the center of the relay are closed by magnetism, this is a reed relay.

In the bulb failure relay there is a coil for the left side lights, and a coil for the right side lights. They are wound opposite of each other, one coil is wound CW while the other coil is wound CCW.

When equal current flows through the coils they cancel out each others magnetic field, and the contacts in the reed relay remain open. If the current between left and right is not balanced (the same) then the reed relay is closed.

The volvo relay is separated into sections, one for low beam headlights, one for park and tail lights, one for brake lights, and one for turn signals.

Any current imbalance in any section will close the reed relay which completes the bulb failure light circuit.

The newer bulb failure relays are electronic.
Click to expand...
 
vlvman said:
The newer bulb failure relays are electronic.
Click to expand...

Nice description. Not sure what you meant by newer, but if you are talking about the 86- relays meant to deal with the high-mounted brake light, there are some "electronics" added.

T3 is the switch for the "3rd eye" closing when both voltage and current are sensed, but not lighting the warning lamp quite as brightly as a failure in one of the two low stop lamps.

T1,T2 form a short timer to suppress the warning lamp flash you may recall occurred in the older version during warmup of slightly unequal but cold filaments.

bfwsDwg01.jpg
 
dbarton said:
I hate this sensor too.

The below diagram is for an '81 240.

If this sensor is needed in the loop, then what circuits are bypassed to eliminate it?
Do we simply connect the light pins to the fuse 15 & 16 pins and call it a day?
Dave B
Click to expand...

Getting to know anything/anyone almost always turns hate into something less. One fellow, and I can't find the post (maybe on brickboard) needed to "delete" his failing sensor quickly, to go on a trip. Using the drawing, he simply pulled the guts out of the can and soldered wires into the base plug around the circuit board to bypass the lamp currents. It was a pretty easy thing to do, he said.

I think he had one of those volvos with the relays in the ashtray, so he could not just simply unpin the connector like one could on a 240.

bfws933.jpg
 
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