Hi there! I have an 85 240GL wagon that I'm trying to fix up. It has a couple of problems that need taking care of before it is road ready. I don't know all the terms for the



The first, and most important, is that I can't get the brake lights to work.

A few symptoms:

The only time I can get the rear brake lights to light up at all is when I have the headlights to full (not highbeams) and turn on the switch between the light **** and the dashboard dimmer switch. At that time, the headlights dim, and only the left brake light comes on. The other running lights seem to work fine, including the reverse lights, but excluding the right turn signal.
If I put the high beams on while the aforementioned is on, the brake lights go off, and then only the right blinker works, though the left turn signal light on the dashboard turns on and stays on.

https://i.imgur.com/pd0Wuxp.jpg Sorry about the darkness of the picture, the only time I had to work on it was at night.

The brakes are always supposed to be hot, meaning they come if the brake is activated even if the car is off, right? Well they aren't. The brake pedal doesn't seem to activate the lights at all.
I changed the left brake light bulb with a fresh one about a week ago, to no avail. only the left one lights up, but only when the foremost mentioned symptom is going.

All of the fuses are good,except for fuse 5. I just tested them all with a meter.



I looked up a bunch of problems that the 240 gets regarding brake lights, and i came up with a few:



The brake switch that is depressed when you hit the brake pedal might be bad
There is a relay somewhere that is bad.
Possibly the Integrity Sensor (Bulb Failure Relay)?





Can anyone help me out? I'm supposed to go to the junkyard later today to pick up a few things, and I'd rather condense it all into one trip. The sooner the better!

 

brake light circuit is very simple, and yes, is always powered.

1) check that fuse 7 is 'hot' (volt meter from either side of fuse 7 to ground).

2) green-red wire from fuse 7 to brake light switch pin 1

3) blue-red wire from brake light switch pin 2 to bulb-out-detector pin 9. insert volt meter probe into back of the BOD (should be PIA!) socket on pin 9, verify that there's juice on this pin when you depress the brake pedal relative to ground.

4a) yellow wire from bulb out detector pin 10 to left brakelight
4b) yellow wire from BOD pin 11 to right brake light.

these 2 yellow wires go through pins 6 and 7 of a 3x3 block connector thats near/behind the fuse box


thats it, the whole shooting match. if you have juice at BOD pin 9, I'd try inserting a jumper between 9 and 10 or 11, and see if that side works, if it doesn't, then its the wiring going to the rear, if it does, then its the bulb out detector, which is a magnetic reed switch surrounded by a pile of counter-wound coils (idea is, if the left brake and right brake draw different amounts of current, then the magnetic field is unbalanced and the reed switch closes and lights the bulb-out idiot light). the bulb out detector is a beercan shaped thing with a circular connector on one end, located somewhere under the driver side dashboard. it might be bright red or blue, but they come in several colors.

IF I had a known defective bulb-out-detector, I'd be highly inclined to chop it open, and gut it, and replace it with a bunch of jumper wires connecting the proper pin sets (for instance, 9-10-11 for the brake lights). recently I looked up all the combinations for a mid 80s 240, and posted them (there's several DIFFERENT BOD's used on different generations of 240 and 740/940, so they aren't all neccessarily directly interchangable, fun fun).