I've got a stubborn "Bulb Out" Indicator light problem with which I could use some help.

I've had my 90 740 wagon for about 3 months and the indicator light was on when I bought it. The only lamps I could find that were burned out were a rear fog light and the AT shift light. I've replaced both and the indicator light still comes on. I've noticed that it sometimes flickers and sometimes goes off when I apply the brake.

Could I have a loose bulb or connection in the rear lamps? Or does the indicator lamp need to be reset?

Thanks for any help on this.
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'90 740 GL Wagon 105K

Hey i had the same problem a while ago with my 760 84 which need to pass its rego.

When i stepped on the brakes the warning light would come on.

I tried everything and finally took it to the auto electrician he fixed it in 2 minutes and sent me on my way happpy. (charged me $5 tho :-> )

Apparently its a poor design,volvo has with their tail lights, the heat build up from the bulbs can melt the plastic surrounds that cover the contact rail.

Both my 740(88) and 760 have this problem which requires my constant attention.
(It helps if u put in the correct lamps) But is cured so easily.

Try cleaning it out with some solvent and see how it goes.
(not sure what the 1990 tail light is like tho)

Good luck
Cheers
David
740(88),760(84),264(75).

I had the same problem with my wagon. I opened the tailgate and worked the left & right brake lights, sockets, bulbs, wiring until I was blue in the face. All were working but still I got the light when I put on the brakes. I forgot all about the middle brake light which was out. How the system checks the three bulbs, I don't know but it does. Close the tailgate before you check to see if all the bulbs are working, it could be the center one.

How the system checks the three bulbs, I don't know but it does.

This bit of Volvo trivia had me stumped too until I autopsied a BF Sensor. The basic principle is that.an equal current thru two opposing coils (having the same number of turns) will have no magnetic effect on the reed relay inside the coils.

The 3-Light Brake Light test circuit is similar, except that the Left bulb is tested by one coil (say 20 turns), opposed by two coils end-to-end, 10 turns for the Right bulb and 10 turns for the High Stop bulb.

As long as all three bulbs work, the 20/20 coils cancel out. However, a failure of any one of the three bulbs will upset the 20/20 "magnetic balance" and the sensor relay will light the BF Light.
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.

False Bulb Failure indications aren't uncommon after several years. Here is how the system works, and some things to check for false lights—

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
The Bulb Failure Sensor tests for a current balance in each of these three groups of light pairs (includes 3 bulb brake lights):

• Tail lights
• Brake lights
• Low headlight beams

You can isolate the problem to one of these groups as described below. The car must be running to activate the Bulb Failure sensor:

1 – Step on Brakes.... If no Warning light,
2 – Turn Parking (tail) lights on.... If still no Warning light,
3 – Turn on Low beams. Should be the cause of the Warning light.

If Warning light is ON when all these lights are OFF (or all tested lights are OK), it could be the BF Sensor at fault.

However, "mismatched" bulbs (different brands, age, or socket condition), or corrosion at the common ground points for Left & Right light housings ) in any of the 3 light groups can also cause a false BF light.

Note that there will be NO warning if BOTH bulbs in a pair are out.

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

Applying the brake is a good indicator of poor connection at the rear. Remove the brake bulbs, you'll probably find some corrusion on the bulb holder or the circuit board. Clean, be gentle on the circuit board.