s50/m50 engine compartment wiring

[Rev Engineer]

Does anybody have any pics of the engine compartment with the intake manifold off? I'm having a tough time figuring out how the wiring harness goes back into place. I think I've got the main section back in, but the section that goes to the alternator and starter doesn't seem to fit - like it has to stretch too far. Also, I can't figure out how to route the o2 sensor wire and the adjacent mystery connector. Suggestions anyone?

Should the wires come into the engine from behind or in front of the heater core hose? Also, any common locations to mount the relays?

[Addissimo]

firstly:

you have a very clean engine, congratulations.

Second:

What the fuck did you do to your wiring harness? It would help if you could post a picture of your full engine bay, so we can see where the ignition coil/fuel injector wiring is going. The case is on the wiring harness for a reason, you're giving me a headache.

If your dme is hooked up already, unhook it so you have more slack in your wiring, get the engine wired up first, then the inake manifold on, then place the dme where you're going to have it.

Life will be much easier that way.

-Addis

[Rev Engineer]

Thanks for the response!

The engine bay is clean isn't it!? I've rebuilt the motor and pressure washed the bay a few times before dropping the motor in.

I'm not sure what's up the harness, maybe that's why I'm having a problem. It was given to me in a box and now I'm trying to unravel it.

The coil and injector wiring seems ok and it's fairly neatly packed into its own plastic carrier. It's hanging over the valve cover on the other side. The DME is not connected yet. I'm right with ya on getting the harness connected before putting the intake on.

The main harness seems to be fitting ok. The connectors to the idle valve, knock sensors, oil pres switch, vanos all seem to be right. But, that big rubber hose seems to be coming pretty far into the engine. It must be like that since the connectors are lining up.

The part which is really f'ked is the starter and alternator wires which come from a different harness section (the big red wires). It'll connect to the starter ok, but when I stretch it to the alternator, then it looks messed like it is in the picture. If I can figure this one out then I'm nearly there. There are some zip-ties around the main harness and the alternator wires. Maybe these aren’t suppose to be there and if I cut them it might fall into place.

The last confusing part is the very long wires which come off the main harness. I'm pretty sure one of the connectors is for the o2 sensor (OBD I has one right?), but I'm not sure what the adjacent connector is for (maybe oil level sensor?). I'm also not sure how this thing wraps around to the exhaust side.

I’ve been trying to compare this to my 97 M3, but between the OBDII harness on that car and the fact that you can’t see shit with the intake on, it’s really not helping me at all.

This part is pretty frustrating. I’m almost done with this project and I can’t figure this crap out. Once I get that intake back on it should only be a few days before I get this thing running. Then it’s onto the exhaust…

I'll get some better pictures posted later.

[FredK]

I'm bumping this topic up, in hopes of solving my own problem. :mrgreen:

The main power cable splits into cables X and Y inside the harness plastic box. I removed the plastic box, and I will protect them later with the 318is plastic wiring cover.

There is a separate cable that comes from the alternator, though it isn't pictured here. Because X and Y are the same exact cable, I hook both of them up to the large 10mm lug on the starter, right?

The alternator cable also will hook up to the 10mm lug as well at the starter, so both alternator and starter are pretty much one and the same in terms of being connected to the battery with a mother-sized cable.

[BDSax]

what year is you harness? ill look at mine tomorrow

[FredK]

Cool. It's the same exact arrangement on both harnesses I have. 1/95 M3 and ~mid 94 325i, both manuals.

[Mike B.]

The last confusing part is the very long wires which come off the main harness. I'm pretty sure one of the connectors is for the o2 sensor (OBD I has one right?), but I'm not sure what the adjacent connector is for (maybe oil level sensor?). I'm also not sure how this thing wraps around to the exhaust side.

You are correct, it is for the O2 sensor. It should be a 4-pin, screw-on style connector.

That other wire (2-pin connector) is for the backup lights and connects to the E36 transmission.