86 740 wagon
My center stop lamp bulb blew so i went to the local canadian tire to see if they had this kind of bulb.. Which they didnt so i got what seemed to be similar. It works.. Buy my bulb failure light comes on when i press the brake pedal.. Is this possibly because it is not the same bulb?? The other 2 brake lights work fine.

 

Yes, these things are very sensitive, the bulbs have to match to avoid the failure warning. Replace the corresponding bulb with the same type.

 

great! I will try this out

thank you

 

the brake lights are particularly tricky because there's 3 of them, and its designed to detect any one or two being out. the detector works by having counter-wound coils around a reed switch, the magnetic field produced by these coils cancels when the bulb currents are balanced.

 

the bulbs in the light clusters are dual filament 5w/21w for the side and brake lights respectively..
The bulb for the centre brake light is a single filament 21w.. however bulbs that fit and look the same are available in 5w, 10w and 21w... my guess is you inadvertently fitted a lower wattage bulb hence the warning light glows.. the voltage and wattage is usually either printed or stamped on the metal part of the bulb just below the glass

 

the brass base american bulbs are DIFFERENT than the chrome base euro bulbs. one spec the wattage at 12V, the other at 13.9V. always use the chrome base bulbs in these cars, the others corrode badly in the sockets.

i thought the high brake light was a 'festoon bulb', tubular with pointed metal ends? or am I confusing my car models again? its been quite a long time since I've had to replace one.

 

Here is what the bulb looks like.
Volvo 240 1986 Bulb 20W Mini Halogen Third Brake Light | eBay

Like i said the local canadian tire did not stock this bulb so i just matched with the closest thing. Will fit the proper bulb asap!

 

Found the right bulb and everything is back to normal!