2002 v70 d5 auto brake light issue

[stephenc]

Hi All,
My mechanic wired my side brake lights to the highline light on the spoiler as they were not working but the highline was. Last night the lights refused to turn off. Even with the brake switch removed the lights stay on. My only solution to save the battery was to disconnect it. Can anyone guide me to the relay that controls the highline light? and why would the light stay on with the brake switch disconnected?. My car is a late model 2002 which I have been informed is same as 2003.
Thanking you in advance

[mikealder]

I wrote this little lot earlier in the week on another Volvo forum but it should help you understand how the circuit works on the phase two, there is a known weak spot with the relay that controls the side brake lights. I would get your "helper" to put the wiring back to how it should be otherwise you will burn out part of the rear electronics module as the portion feeding the center brake light is only designed for a 3W load and the way he has wired it up presents a 45W load which will damage the REM (it might have already damaged it but we can resolve that issue later). Please consider the text below was written in response to a direct question about brake light failure. (A missing fuse was the answer to this issue but I doubt that is what is wrong with yours).

Lets start with the wiring diagram and an explanation as to how the circuit works that I hope will make sense to you, you do indeed need the fuse 11D/14 installed as there is no way for power to pass to the rear outboard brake lights when this is missing - No idea why it is removed from your car and I would far rather trust the Volvo diagram than a generic style diagram in a Haynes book. 11D/14 should be rated at 7,5A.

First the diagram which I have colour coded to make it easier to follow in the text below:



Lets start at top right with the fuse 11B/12 this feeds battery voltage to the brake pedal switch, with the pedal switch depressed the 12V travels through the yellow wire going through connector 54/3LG pin 12 before going to the CEM arriving on pin B4. The CEM then inverts this signal prior to feeding out a discrete signal to the REM on the green and yellow wire routing through connector 54/43 pin 13 which is under the left hand side of the rear seat base.

The REM now does two things with the 0V switched signal going in on A4, firstly it provides a +12V output on D4 which is a yellow and red wire this passes through the tailgate connector 54/78 pin 3 where it changes to a yellow wire routing to the center brake light. The other thing the REM does is to energise the brake light relay.

All the above is working on the O/Ps car which explains why you can hear the relay clicking when you operate the brake pedal.

From this point I will detail what should be happening:

+12V is fed through fuse 11D/3 which goes to the brake light relay, when this relay is energised it feeds power out on the yellow wires to the trailer socket 54/51 pin 4 and to the Shunt RSH6 which provides bulb failure detection for the brake light circuit, the yellow wire from the center of RSH6 feeds power to fuse 11D/14 (7,5 Amp rated). The output of fuse 11D/14 is a green wire feeding power to splice 53/667 which is in the main wiring look under the REM, the splice is a small black heat-shrink covered metal barrel containing three green wires. The two green wires then connect to the brake light bulbs on both sides of the car.

Try refitting a 7,5A fuse to 11D/14 then see if the brake lights work, if not take the REM off its mounting structure and have a good look at the rear of where the brake light relay is located, check the two yellow wires are still connected to the relay base and not damaged (as in burnt out from connecting the defective trailer) - Hope this helps - Mike

[stephenc]

I undid the mechanics wiring bodge but the highline light still has constant power to it and won't switch off I'm trying to trace backwards as per your diagram but having removed the relay in the REM the light still has power

[mikealder]

The high level brake light isn't driven by the relay it is switched on/ off by electronics within the REM (Rear Electronics Module) it is this electronic bit that has probably packed up by being overloaded while trying to run all three brake lights from it.

The wire causing the center brake light to be on all the time is the yellow/ red wire which leaves the REM on pin D4 - For now I would simply cut this wire to kill the center brake light.

Change the relay RMI5 and get the rear side brake lights working again then connect the previously cut yellow/ red wire to pin 4 of the trailer socket 54/51 which is at the rear of the car tucked up under the wiring loom where it crosses the rear of the car - Mike

[draser]

From the schematic - it looks like the driver for the high brake LED light in packed in the light itself, probably on the same circuit board. It seems that the driver is shorted out - hence light on all the time. You'd have to remove the circuit board from within the high brake light, and either replace or troubleshoot (replace burned driver).

[stephenc]

The car went back to the mechanic who got the side brake lights working again as they should have been all along, He identified the always on highline light as a short and disconnected it entirely. Thank you for your help Mike and Draser, I will get around to re-routing the highline to the trailer socket as suggested. Thanks again