hi all,
i replaced most of my exterior lights on my 88 245 wagon with leds, everything works fine and looks really nice, but when i put in the 1156 bulb type LED for the high mount stop light, it triggers a bulb out warning when i brake. does anyone know what could be going wrong? thx

 

Well, I know what is going wrong but not necessarily why...
The B/O relay works on resistance from side to side. That's why often times when replacing one bulb on the circuit (for instance left brake right) you end up replacing both sides with the same brand and newness bulb.
Assuming you replaced the left and right brake lamps with LEDs, the resistance should still be equal. The issue is where does the high mount draw its power? I don't know w/o schematics in front of me. My suspicion is it piggy backs on one side or the other but how Volvo originally got around the uneven resistance I have no clue. Are you certain it is the high mount that causes the false positive on the B/O relay?

 

yes, i when i put in the incandescent in the high mount it is fine, but when i put in the LED it triggers the warning...

 

Well, it would seem that there must be some sort of resistor in the factory wiring to balance out the left and right sides of the brake circuit. Whichever side the high mount is not connected to must have additional resistance equal to the the amount generated by the high mount bulb. Since the LED has much less resistance than incandescent, the system is unbalanced. So, the convoluted solution is to place a resistor on the line with the LED high mount equal to the difference between the LED and an incandescent bulb. The simple solution is to just run an incandescent in the high mount.

 

"The simple solution is to just run an incandescent in the high mount."
omg...then it won't be awesome

 

I looked at the 1990 wiring diagram and 12 VDC is supplied from the BULB FAIL SENS Pin 5 tp the Hi Stop Light, the other side of the Hi Stop Light is connected to ground. It would appear something inside the BULB FAIL SENS doesn't like the current draw from the LED.
I have A 1990 245 with LED STOP/TAILLIGHTS in aftermarket taillight assemblies, because running incandescent 1157's in the aftermarket version will surely melt the housing. The high light, is a let sleeping dogs lay approach for me.

 

What LEDs did you use & where'd u get them?

 

LOL...yeah, well, er, hmmm...
awe·some   [aw-suhm]
adjective
1.
inspiring awe: an awesome sight.
2.
showing or characterized by awe.
3.
Slang . very impressive: That new white convertible is totally awesome.
Under the hood of your 88...this would be awesome...


This...in the high mount? Meh...not so much...

 

LED Brake Light, Turn Light and Tail Light Bulbs - Super Bright LEDs

Use RED LEDs in this application.

I don't remember exactly which ones I got for the 1990 245. It was not the SMD type. I think it had 18 LEDs, they did not trigger the Bulb Failure circuitry, and worked pretty well.

I got the SMD for my 1997 965, and you can not tell the difference in them and an 1157, however they trigger the bulb failure relay to turn on the light in the instrument panel. Taillights trigger it independent of the brake light, and the brake lights trigger it with the taillights off. One day I will get around to addressing that, but for now it is enough not to be melting the aftermarket taillight assemblies.

 

Another definition:

Awesome: A certain 1990 Volvo 740 GL with Texas Tags.

 

i dunno if that engine would be so awesome on my gas mileage...:\
anyway...i think i'll try using an ohmmeter and trying to add resistance to the circuit somehow...:\

 

Pull the light from the cluster for the bulb warning and you can get some sleep. Honestly those LEDs should never burn out anyway. I just find the whole bulb out warning system to be quite annoying. That bulb has not been in the cluster since I bought my car.

 

well, i prefer that the bulb out works...it would lose it's awesomeness otherwise.
i'd rather have an incandescent in the high mount than the bulb out not signaling.