I posted this to the volvo group I belong to on Facebook, but thought I’d see if anyone might have an answer further out in the world.

I’m really scratching my head on this one and could use some suggestions. Have a 76’ 245 Volvo. Rewired the back from the fuse panel. I’m getting current through everything correctly, used a volt meter and a toner and probe to make sure. My brake lights, reverse and hazards won’t come on. Parking and turn signals do work. Switches and relays all seem to check out. My indicators are showing on the dashboard. I pulled the light indicator and carefully opened it, to check connections (they look




alright). Would the light indicator prevent those lights from working (relay failure security sensor 1234652). It is a discontinued part. It’s very pricey to get from eBay on a whim. Any work arounds?

 

Your bulb failure relay - only cares about the rear parking lights, the low beam headlamps and the brake lights. The wiring going to it only goes to those 7 (or9, if 4 taillamp) bulbs. The numbers on the relay case - such as 54l, 54r - are left and right to whatever #54 is. You should be able to figure out what wire feeds the brake, rear parking lights, and low beams. That relay has nothing to do with the reverse or hazard lights. Hazards - there is a separate fuse for the hazards and turn signal wiring goes to the back of the hazard switch. Reverse lights - check the switch, undo the 2 screws on the shift indicator to get to the Neutral/reverse switch, there's a 4? wire connector at the end of a short harness, you can check power in and out, on an automatic. On a manual the reverse switch is on top of the trans, wiring comes through a hole in the transmission tunnel. .

It's interesting how that relay works - how it knows a bulb is out. Looking at the two tone coils - there are three, (park, headlamp, brake) The current for each bulb on each coil is wound opposite - top to bottom on one wire - bottom to top on the other. The coil will create a magnetic field and if the current used by each bulb is not equal - and close the magnetic reed switch in the middle of the coil, turning the bulb out light on. Figure out how it knows the 3rd brake light is out - it's been a long time since I've had on of those apart. Maybe it uses that resistor -