Rear brake light upgrade
 

Hi Folks

I was following this upgrade and did it a while back great mod and cheap/easy to do Now for the downside (on mine anyway) decided to sell an old bike trailer and thought i'd check it was all working lights etc noticed a fault ie. when car was running brake and side lights were on together permanently
tried with a light board same result which pointed to it being a fault with the car wiring decided to return the rear light wiring back to standard and all lights now worked as it should So if you have done this mod and have a towbar check your lights work ok

So the question is; does this loss of function only happen with the DIY resistor mod from Maplins or does it also happen with Evgeny's bespoke module? If his module doesn't cause this loss of function, then it is actually worth the money as he deserves recompense for the effort and skill in developing a foolproof mod. If not, his mod is just a two penny resistor and the rear lights were best left in original state if you have a trailer.

I have Evegny’s light module and tow a double axle trailer behind my 2013 XC70. No problems whatsoever with lights playing up.

Johnny Kebab

It looks like the side and brake lights are hard wired together. You would need to isolate them using diodes to stop one voltage line feeding back up the other.

As said above - you need a resistor AND a diode to stop back feed into the brake light circuit.

Am also surmising your tow bar is wired with an after market electrics box rather than the proper Volvo trailer module?

towbar was fitted by a company who specialise in towbars tho they did the basic mistake of wiring with the tailgate open

Different lights come on when the tail gate is open which are not normally illuminated when its closed. They clearly didn't test their work afterwards.