Originally Posted by Protegimus
As an addendum to my original post containing the schematics and with a big thanks to ossie cossie for figuring out the correct (180ohm) resistor value, the following diagram gives the correct wiring to allow all four tail lights as sidelights; brakes lights remain high intensity on the two inner (original) lights and the third high level spoiler light, plus optionally operate as four brake lights (with outers at normal intensity) when the sidelights are switched off:
Bit of advice during installation - the plugs undo easily once the retainer is unclipped, press down on the central retainer with a small (4mm) flat blade screwdriver then pull the harness out:
Standard connector pinout - I used 1N4001 diodes. The feed from the brake lights to the tails lights (diodes A & B for four brake lights with sidelights off, which is optional) is already spliced:
Now the brake light feed is cut ready to splice in the 180ohm metal film resistor and diodes C & D:
Heat shrink insulates and supports the soldered in components - it is only a few pence and much better than insulation tape. Cut to length and borrow your Mrs. hairdryer to shrink:
Thanks. Very useful post. What should be the wattage for the resistor?