In our opinion, the best harness for this swap is an early manual 93-94 325I harness. It's simple and can be acquired from any junkyard for cheap. Not to mention, you won't have to sit there and eliminate wires you did not use. However, if you got a harness out of an auto car it can still be used. You can just cut out all the wires associated with the auto trans.
To make this adapter clean, simple, and removable you will need the the harness plug from an e36 engine side, and the body side of your e30s harness. Below we have compiled a list of pin outs to assist you in wiring. Although this is close, every year is different. This should not be used as your only guide.
89+ cars do not have an ABS relay separately, they rely on the main relay. Since that needs to be removed when you take out the old harness. This means you need to power the system through another way.
The best way to do that is to look on the chassis side of C101 (big round plug). Locate pin 20 (its a red/yellow wire). This is the is ABS power wire. You can run a wire between pin 20 on the engine side of E36 engine bay wiring harness and tap into the relay port 87a (red/white).
On eta models the signal signal for the MPG gauge and the tach signal are in the glove box. Pin 14 on the E36 connector for the speed signal goes directly to the green plug on the back of your instrument cluster.
Don't forget to put your e30 coolant temp sensor for the ECU on your m50 engine or else the coolant temp gauge will not work.
|E30 Wiring body side harness||318is||325is||E36 m50 wiring engine side harness||Color|
|Pin 1 - alternator||Blue||blue||Pin 25||blue|
|Pin 4 - coolant temp||red and white||Brown and purple||Pin 12||green and grey|
|Pin 5 - oil pressure||Brown and green||Brown and green||Pin 23||green|
|Pin 6 - Diagnostic Connector||Green and white||green and white||Pin 22||green and white|
|Pin 7 - Ignition||Green||green||Pin 21||green|
|Pin 8 - MPG gauge||White||white and black||Pin 24||white and black|
|Pin 9 - engine speed||Black||black||Pin 20||black|
|Pin 12 -check engine||Brown||grey||Pin 8||grey|
|Pin 13 (fuel pump)||Green and purple||green and purple||Pin 13||green and purple|
|Pin 14 - speed signal input||Black and white||black and white||Pin 14||black and white|
|Pin 15 - starter thin wire||Black and green||black and green||Pin 15||black and yellow|
|Pin 18 - starter thicker wire||Black and Yellow||Black and yellow||Pin 18||black and yellow|
Please be aware that there are too many variances in models and your wires may be different. This is just a general guide. Here are some other resources to help you along:
General info - Garagistic DOHC swap basics
More wiring - http://www.akgmotorsport.com/e30convpins.html
Yes, it's possible to use the Getrag 260 transmission (the 5 speed found in most e30 6 cylinder cars from the factory. This transmission is great because the final drive on the highway is .83 as instead of the 1.0 ratio that would have came from using the Getrag 250 from an e36. That translates into roughly:
With a 3.91 differential and 1.0 ratio, engine would be spinning around 4500 RPM on the highway with with the Getrag 260 and a 3.91 and the .83 final gear, its more in the area of 3200rpm.
So what's needed to get the transmission to work in DOHC swaps like the m50 or s50? Well, the Getrag 260 sits about 10 degrees to the right of where the 250 would. This means that the transmission brace needs to be changed. Which we offer below:
A smaller brake booster is needed to clear the intake on the brake booster. Some use a 320 booster or smaller unit. There is another idea. A boosterless brake setup using Wilwood/Tilton pedals gives the engine bay a clean look along with less cluster. Everything is tucked under the dash, except the reservoirs. Click here to read about this method.