By shagrath, Mon May 09, 2011

Original thread: Radio wiring write up

How to install an aftermarket radio on the factory harness without rewiring the whole car. This walkthrough uses diagrams 6500-0 and 6500-1 (pages 99–100) from the 1987–1988 BMW 528e ETM, with premium sound. Cars without premium sound are a more straightforward rewire. Ignore all fader-switch wiring.

Wire colors below are ETM colors: VI/GY is violet/grey, RD/WT is red/white, BR/BK is brown/black, and so on. See also Electrical for the rest of the ETMs.

Aftermarket harness colors

These are typical. Confirm on your unit.

• Red — main (switched) power
• Yellow — memory power (keeps presets; does not turn the radio on)
• Black — ground
• Blue — remote (aftermarket amp)
• White — dash-light dimming or power antenna
• Speaker pairs: purple, grey, green, white; the same color with a black stripe is the (−) side

If the radio turns on but will not keep memory, the red and yellow wires are backwards.

Power and ground

Using diagram 6500-0 (page 99):

1. Find the VI/GY (violet/grey) wire that changes at a connector to VI/WT (violet/white). This is main power. Splice the aftermarket red wire to the VI/WT side, omitting connector C216. The VI/GY in the car is looped and looks confusing — tap the part that goes back into the dash.
2. Find the RD/WT (red/white) wire. It will be connected to a yellow wire. Ignore that yellow wire. Splice the aftermarket yellow memory wire into RD/WT (unless your radio uses a different memory color).
3. There are two factory white wires. One runs with the antenna cable (raise/lower). You can try splicing it if your radio has a power-antenna output; many people use a separate switch instead. The other white wire connects to GY/RD and goes to the light switch for auto-dimming. It can be left unused.
4. Ground is BR/BK (brown/black). Splice the radio's black wire here. If BR/BK is already tapped to a solid brown (BR), splice to that.

The radio itself will now power up. Speakers are the rest of the job.

Speakers — run new wire up front

1. Run new equal-length wire to both front speaker tunnels for both the front and rear channels: right front/rear on one side, left front/rear on the other. Tuck it behind the kick panel and through the glovebox. Leave at least 4 inches in each front speaker tunnel. You do not run new wire to the back of the car.
2. Diagram 6500-1 (page 100): wire the front speakers. On factory E28 fronts the two sides are opposite each other on the speaker. GY/GN (grey/green) is the tweeter. Remove the two factory front speaker wires and splice the new wires from the radio (the pair for that speaker — remember you ran four wires into that tunnel). Repeat for the other side. The fronts are now entirely on aftermarket wiring.

Rear speakers — use the factory amp runs

The factory amplifier wiring already goes to the back of the car. Use it as the rear speaker run.

1. At the right front speaker, diagram 6500-1 shows GY/BR (grey/brown) and GY/WT (grey/white) going to the amp. Splice the two leftover radio wires (the rear channel for that side) to those two. One side of the connector looks messy; splice it and move on.
2. The left side is the same idea with GY/VI (grey/violet) and GY/RD (grey/red).

Bypass the trunk amp

Unplug the amp in the trunk and pull the harness out far enough to work. Cut the wires listed below and splice matching letters together (A to A, B to B, C to C, D to D):

Pair	From amp harness	To amp harness
A	GY/BR (grey/brown)	BK/WT (black/white)
B	GY/VI (grey/violet)	BK/VI (black/violet)
C	GY/RD (grey/red)	BK/RD (black/red)
D	GY/WT (grey/white)	BK/BR (black/brown)

Tuck everything away. The factory amp is out of the system; the rears are driven directly. This can be put back to stock — no cutting of the fader switch, and the factory wiring is still in the car.

An '88 ran this layout for two years with no failures.

From the discussion

Discussion thread: Radio wiring FAQ discussion. Shagrath later confirmed the write-up above is correct as posted. A promised photo set and a non-premium-sound follow-up were never added.

Useful additions from that thread:

• The factory radio power harness is already fused. You do not have to move the head unit onto the auxiliary fuse panel. If you want to anyway, see t=53571.
• Swapping memory (constant) and switched power is the most common install mistake — the radio turns on but loses presets, or will not turn on at all.
• Factory wire colors in the car can disagree with the ETM if a previous owner has been in there. Confirm with a meter, not just the color.
• Cars without premium sound are a simpler rewire; this page is the premium-sound / factory-amp case.

Keep-the-amp shortcut (lmc337): unplug the fader wheel, connect the aftermarket head-unit speaker positives to the matching fader-output pins (Chip Baines's old stereo-upgrade page had the colors; the site is gone), and leave the head-unit negatives disconnected / tied off. The factory amp stays in the circuit, no speaker wires are cut, and a stock head unit can go back in in minutes. Two-plus years with no speaker issues. Caveats: the radio can cut out on the brakes, especially with an extra brake light and on wet days, and an old fuse has been known to pop.

Chip Baines's stereo-upgrade notes used to live at eabjr.com (dead, same as the OBC page).