The vast majority of the stock wiring was removed from the car during deconstruction, which I covered in Part I of the build.  Fortunately the stereo harness was completely separate from the rest of the chassis wiring.  I still had to go wire by wire for things like electric windows, seat controls, HVAC, airbags, and interior lights.  I picked up a depining tool set from ECS to help remove the wires completely, all the way to the fuse box.



This was certainly a daunting task, but taking it one wire at a time and labeling everything helped to insure no needed wires were cut.  The remaining chassis harness was fairly simple, just operating the tail-lights, fuel pump, wipers, head-lights, and instrument cluster.  I left the OEM chassis computer in place so that the wiper stalks to operates as normal with intermittent settings.  I also left the OEM light control unit, so I can still have turn signals, high beam, and flash just like stock.

The engine bay side was fairly simple as well, just removing the emissions related equipment, HVAC control (heater valve, AC compressor wiring), horns, washer level & pump, hood switch, foglights, side markers, and washer nozzle heaters.


A lot of weight can be lost here by swapping to a lightweight ATV/Motorcycle battery.  I knew my car would be a little heavy with the cooling shirt system and differential cooler at the back (not to mention a heavy driver) so I decided to lose the boat anchor stock battery.  I’ve used the Deka batteries in the past and had decent results.  I wouldn’t recommend one for a daily driver, but they work well for a race car.  These are the same batteries sold under Braille brand and other store brands, yet much less expensive.  This ETX 16 battery weighs in at 16 lbs and easily cranks the M54.

I made a simple battery bracket out of aluminum angle stock, which was riveted to the OE battery floor.  A piece of U-channel aluminum, threaded rods, and wing nuts made for a custom hold down.  The stock grounding lug was used with some longer cable.

Deka ETX 16 Battery


Power Wire

In the photo above you can see the power cable as it runs from the battery positive terminal and forward to the kill solenoid.  (note: the kill solenoid should be oriented with its terminals on top, I have to fix this.)  This is the electrical kill setup from BimmerWorld, which uses a heavy duty solenoid to kill power rather than a mechanical switch and pull cables.  The small circuit breaker is also part of this system.

The stock power system uses two wires running from the battery forward.  One is fused and approximately a 2 gauge wire that runs to the fuse box.  The other larger wire (apprx 1 ga) runs through the firewall to the under-hood jumper lug and then to the engine harness (starter and alternator.)

Since I was pairing down the electrical system to the bare minimum, I deleted the smaller wire and ran a single wire from the battery up to the firewall.  At that point it needed to be split so that power could run to the OE fuse box and continue on to the engine.  To accomplish this I used a GM/Delphi battery terminal box.  I trimmed the plastic a bit to allow the cables to exit, then mounted the box behind the passenger side foot protection bars.

SpecE46_IMAG2660 SpecE46_IMAG2651 SpecE46_IMAG2654


Also running from the GM battery terminal is a smaller 10 ga wire, used to supply power to switch panel.  I used a Hard Motorsports dash panel kit as my basis for the switch panel.  I got a box full of K4 switches and circuit breakers and mounted everything tightly on the upper (formerly vents) section in the center of dash.  For circuits I planned for the following (from left to right):

Backside of switch panel in progress

1. AiM MXL Dash
2. MyLaps Transponder
3. Radio power (future)
4. USB power (originally for GoPros, now a spare)
5. Differential cooler (two pole, 1. for pump, 2. for fan and pump)
6. Helmet blower
7. Seat blower
8. Cooling shirt pump
8a. Cooling shirt timing rheostat

Each of these circuits have a corresponding circuit breaker directly below the switch.  Power is distributed across the supply lugs via a solid metal bus bar.  From there short lengths of wire with ring terminals run to the individual switches.  Switched power then runs out to Weatherpack style connectors to allow for removal/installation of the dash without much fuss.

Assembling Switch Panel Partially Wired Switch Panel

Weatherpack Connectors Switch Panel Installed