The dashboard "Bulb Failure Light" recently came on in my '84 245 Wagon.

My right headlight was out. I bought a Sylvania H4656 from Ebay and put it in. The headlight worked but the warning light remained on.
The warning light was on only when the low beams were switched on. It was off for high beams and off for running lights. The two working bulbs must have enough differential voltage drop to turn on the "Bulb Failure Warning Light!"

I bought two Sylvania H4656 bulbs (from IPD) and put both in. The lights now work and the warning light is off!

The picture below is of the WORKING bulbs that caused the problem. Notice they are both Sylvania H4656.

 

That thing is too sensitive! We have all experienced that with unequal type bulbs, very frustrating. Only remedy is get rid of it--most cars that vintage don't even have it but Volvo for extra "safety" started using it years ago. Now all the techno boxes have it.