Re: E28 Amplifier Wiring

[Erick Baumeister <erickbau@xxxxxxxxxxx>]

Rob, Good writeup on the E28 aftermarket amp setup!

A couple of things I did differently on my '88 535i when I installed a
Kenwood amp over Thanksgiving.

1. Installed an amp mounting/chassis isolation board to the underside of
the rear deck. I countersunk and wedged hex head machine bolts in the
board and secured from above with nuts and delrin washers. I used a
scrap piece of 3/4 inch plywood cut to fit the underside of the deck.
This allowed me to secure the amp to the board on my workbench instead
of fumbling with it and the wiring upside down in the car. The board
prevents chassis grounding of the amp.(no metal/metal contact)which can
introduce noise into the system. I also found that the Kenwood amp was
too wide for the mounting spot and would not clear the trunk hinge rods
without the board as a spacer. So I solved two possible problems with
this setup.

2. I ran power to the amp in the trunk straight from the battery so I
tried to find a different route to avoid the RCA cables picking up noise
from the power cable. Of course this would be much easier in an E28 M5
(trunk-mounted battery) but the battery in my 535 is still in the engine
compartment so here's what I did:

I used 8 gauge cable with a 40 amp inline fuse 1 foot from the battery.
I then ran the cable through one of the oval knockouts in the
firewall(The ones that always fall out). Since mine was already out I
drilled it for the power cable and also another 2 conductor cable that I
use to turn the aux. fan on in the summer via a dash mounted toggle
switch while retaining the temp sensors...but that's another story....I
then pried up the driver's side door threshold and ran the cable under
the carpet(finding another displaced  oval knockout along the way) to
the threshold and tucked it underneath. I also took this opportunity to
run the remote turn on lead from the head unit along this same path.I
repeated the door threshhold scenario for the rear door and through the
stock knockout on the door side of the rear seat behind the carpet. The
power cable meets the RCA cables at this point on its way to the trunk.
I also used the grounding point under the rear seat for the amp.

Cable requirements:
between 14-16 feet of power cable
between 12-15 feet of remote turn on wire
12 feet of RCA cable(I used StreetWires Zero Noise 2.0) 

I'm running a Toshiba CD indash unit(not that great) with the stock
premium speakers. Sound quality is improved immensely with the amp and
16gauge speaker wire. The stock speakers actually do OK with decent
wiring and more power.
 Absolutely no noise interference at all. Next steps(maybe, on my wish
list for now) are a subwoofer under the rear passenger seat, a Becker
Mexico headunit and CD changer under the rear driver's side seat, and
upgraded speakers all around. I may try replacing the capacitors in the
stock front crossovers if I can find a source of quality caps(anyone?).

Erick Baumeister
Livermore,CA BMWCCA #131280
'88 535iA, Dinan Stage 3,etc...
and since we're on the thread, Glock 17, Serial# AA***

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