*****I was quite happy to attempt this modification to my own vehicle but I cannot be held responsible if you damage your vehicle in an event to follow my guide.*****
E46 Saloon Numberplate Light Upgrade Using E46 Coupe Light Units and Reflectors
I had to do this light upgrade as a corroded and poor connected numberplate light switch was affecting the boot release microswitch
causing the boot not to open via the boot lid handle.
I'd already purchased a donor Coupe boot lid handle from Quarry Motors after receiving this lighting upgrade advice from forum member dailydoggy(Cheers ).
1) Open boot, remove all the plastic connectors fixing the boot lid carpeting and unscrew the 2 carpeted screws holding the tool kit.
2) Locate the wired electrical connection plug and unplug it.
3) Using T20 Torx attachment uncsrew the 4 screws securing the boot lid handle to the boot lid and carefully remove the handle and its wired plug.
4) Carefully peel back the gasket and put it somewhere safe and clean.
5) Remove the Coupe light units from their holders, cut the wiring then hacksaw the holders as per pic.-
6) Using a dremmell type tool, linisher and/or hand files trim up the plastic on Coupe light units and in the saloon boot grip
so as they slide into the area vacated by the saloon light unit.
7) As you can see the Coupe light units are taller than the saloon ones so I cut elongated the bulb electrical connecting strip so as it housed the bulb lower, then bent over the connecting strips.
8) Again using a dremmell type tool, linisher and/or files keep removing the excess material from the holders until they are a snug fit
sat in the saloon numberplate light molded recess.
You basically end up with the rectangular frame to hold the reflector. Trim the reflector if necessary.
9) When you're happy with the fit stick it in place, I used a hot glue gun but araldite will do fine.
10) Cut the 4 tabs off the lid on the Coupe light unit and remove it until later, this exposes the wiring.
Fit the light units into the boot grip and fix in position with a couple of glue dabs.
11) Strip back the wiring on the new light units and the boot grip. Solder like for like wires together and protect with heat shrink.
12) Using multimeter check continuity of lighting circuit and circuits with boot release micro switch in open & closed position.
13) Reconnect the boot grip wiring plug to the mating plug in boot.
14) Switch your lights on, check numberplate light illuminates and confirm the boot release works.
15) Trim the coupe light unit plastic lid so as it just sinks into light unit and glue in position.
16) Repeat process with the other numberplate light unit, replace the gasket, thread wired connection plug through boot, reconnect the electrical plugs, check operation, replace tool box and screws and finally refit the bootlid carpet securing with clips.
Just to help keep the moisture out I ran a thin bead of transparent silicone around the reflector, easily removed should the bulb ever need replacing.