The brake lights on my 91 240 have stopped working altogether. I had only one side working for months so I ignored the issue but it’s my daily so I need to address it quickly. The fuse and the bulbs are all good, replaced less than a year ago and I’ve inspected them all. The taillights themselves are less than two years old. I don’t think it’s the switch under the petal as that wouldn’t explain why one side worked for a while. Could it possibly be the bulb failure sensor and is there any good way to test it? Looking to see if someone has a similar issue before I go spending money on parts.

 

Does your 3rd brake light work?

Use your $5 test light to see if power is getting to the taillamps, There are many possibilities so diagnose before "spending money on parts".

 

Yeah I used a meter to check voltage, something is preventing it from getting voltage to the taillights. Running lights, turning signals and reverse lights all work. I’m leaning towards the bulb failure sensor but I don’t know how to diagnose if it’s gone bad or not. I also don’t know if there are other components that could possibly be at fault

 

Power goes from -
Brake light fuse
brake light switch
bulb failure relay - should be able to find the wire from the switch at the relay - (It should be the same color)
and then the 3 wires that go from the relay to the 3 brake light bulbs (sorry don't have a wiring diagram, but it's pretty obvious)

I have seen cracked solder joints in 240 bulb out relays - and fixed them with a soldering iron. The terminals (in and out for each bulb out function, park, low beam and brake) are clearly marked, and the cover easily prys off exposing the insides.