V70 lower rear brake lights not working

[V70RMW]

I know there has been the occasional question on this but I think I have exhausted the usual problems.

Check brake light comes on when braking and both lower rear brake lights are not working. I changed both bulbs with no difference.

I checked Fuse 3 in the rear fuse box, looks ok, so I replaced the double relay unit 9494782 with 2 x 8651661 relays from dealer. Still not working.

Car is a 2001 V70 2.4T. All other electrical bits on the rear hatch work (other lights, reversing lights, rear wash and wiper, etc). Centre high level brake light works fine.

Now a bit stumped so I would appreciate any advice. Thanks.

[outnumbered]

Have you checked the wiring at the top of the tail gate.
mike

[V70RMW]

Wow, quick response. I haven't on the basis that the lower lights wiring won't run through there, only the upper brake light, the wiper, washer and HRW which all work fine. Will have a go if you think worthwhile though.

[mikealder]

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, we know the circuit up to this point is OK because the high level brake light is working. The other thing the REM does is to energise the brake light relay, can you hear/ feel the relays click when you (or a helper) presses the brake pedal)

+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). You should check that RSH6 Shunt is still fully connected to the REM or did it get disturbed when you popped the relays out for changing them.

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 fitting a new 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. - Hope this helps (My money is on fuse 11D/14 being either missing or blown - I doubt it is the tailgate wiring in this instance as that portion works correctly - Mike

[Missing Lincs]

This doesn't crop up so much with Volvos as they have dedicated wiring for a trailer socket, but sometimes people try a bodge to install a trailer socket. I'd have a quick look if there's a trailer socket or traces of where one might have been removed. Often these type of installs feature 'Scotch-lok' type connectors, tape and other dodgy connections.

[jnmonaghan]

The notes i keep on this issue indicate the replacement of the double relay,which covers positions RM15 & RM16 with --
In RM15 relay part No 30765030.
In RM16 relay part No 08651661

Jude

[mikealder]

The usual fault is when an owner follows the Haynes book which states fuse 11D/14 in the REM is a spare so it gets used for something else when in reality it isn't a spare as the Volvo diagrams prove so when the fuse is pulled the lower brake lights fail to illuminate.

A bodge on a trailer socket won't cause this fuse to blow assuming the trailer socket wiring Volvo provided is used - Mike

[V70RMW]

Thanks for all the advice chaps. There has never been a fuse in position 14 so I suspect that an early car is subtly different. Doesn't mean an equivalent fuse isn't somewhere else I suppose. I used the wiring diagram from here http://www.volvowiringdiagrams.com/v...20Diagrams.pdf
and did wonder whether shunt RSH6 could be the problem. I will check this out as well as the module itself.

A dealer fitted towbar when I bought the car used (8 years ago) could well have been a bodge so will check that too.

Having the actual wrong relay would undoubtedly be a problem so will have to check. I did think they were both the same but you could well be right.

Thanks again all.
Richard