Bulb fail warning light

Should have said!!

I have a 89 740 (UK)

I do like this sensor, but it can be a right pain. The sensor works on the resistance of the filament of the bulb, and is obviously "paired up" with the other bulb on the opposite side of the vehicle.

I have known it to light continuously, because the two of the bulbs in my brake lights were made by different manufactures and had differing resistances.

You need to check that all the connections to the bulb and bulb holders are clean.

Or perhaps replace both stop lamp bulbs.

hope this helps,

Steve.

I had this on my 740's, most common cause I have found, apart from mismatched bulbs, is oxidisation on the bulb contacts, or on the holder contacts. Make sure everything is clean and buy bulbs in pairs.

Stuart.

This specific glitch is usually the third taillight - it is gimmicked into the system and is the one blub that is on both circuits.

Either that or a loose solder joint in the taillights.

Thanks for that, but can you tell me what you mean by the "third taillight". I have red rears for the dark, brake lights, reversing lights, one fog lamp and my number plate light. It is a term that we don't use this side of the pond.

Thanks

Bill

Bill,

I did not see anywhere where you stated the model.

I had that fault develop on a '99 V70 T5 about a month after I bought it. The vehicle was under a years warranty so I took it back three times and they never found the fault. They changed the bulbs, checked the connectors, which were all like brand new, checked the earth runs and changed the sensor pack.

The sensor pack is a switch relay with reed type connectors which should switch simultaneously and only fail to do so if there is a variation of amperage drawn through either coil due to a fault or mis-matched bulbs.

The usual cause is a bulb on the way out and it's resistance has gone up\down realtive to the other and the cure is to change both. Mine was due to none of the standard reasons I have seen on any Volvo boards and I just resigned myself to living with a momentary flash of the bulb out lamp which had no pattern, other than foot brake operation. I had a career in electronics and would have loved to have nailed the problem with a multi-channel memory scope but other factors in my life were more important.

The fault, which I always suspected was a floating voltage (lack of lock down on stability of the power rails) ended after a battery change 6 months after I bought the car. Some batteries die very slowly, as did mine, but many just fail out of the blue. I feel sure that many of the Volvo electrical gremlins are due to battery related issues and saw in the last month of mine, onboard computer zeroing, clock going to 00.00 and three Electronic Throttle alarms. I put the biggest, best 4 year warranty battery on and have never seen a problem since.

Liam

He means the highmount or center brakelight, it's mounted in the lower middle of the rear window, IIRC it wasn't included unil '86, so if you have a very early '86 it may actually be an '85 model, that light being one of very few differences.

I realised that ommision as soon as I posted my intitial query, and put in in the post "Sorry, '89 740GL".

Reading yours and the other replies, perhaps I'll live with it until something else goes.

Thanks

Bill

It probably just means that the bulbs don't have *exactly* the same current draw when first lit, but the difference isn't enough to trigger a constant warning from the circuit. Knowing Volvos, though, it could also be a bare or loose wire, somewhere...