Need Electrical Help

[Wh33lhop]

So, long story short, '87 325i and '92 525i M50: when my oil level sensor is plugged in, there's a short in the system, when it's not, there seems to be no short.

Longer story: I had the battery hooked up :oops: and went to connect the grounding strap to the motor mount arm, lots of sparks. Hmm. I saw one of the small striped ground wires in the harness was roasting itself, so (after disconnecting the battery) I traced it to the oil level sensor. The other 2 wires in the connector seemed fine. I didn't have a DMM on me, so I tried pulling the harness plug from the oil level sensor, reconnecting the battery and connecting the ground strap again. No drama. Confirmed by reconnecting the harness to the sensor and sparking again.

Although I couldn't see how I could have fucked it up, I thought maybe I had hooked up the power/ground wires on the terminals wrong. I really don't see how I could have boned this up, but just to double check:

Starter ground obviously goes to ground
Harness lead to ground
From the fuse box, smaller lead to power and larger lead to ground

And a few more things just to confirm:
I'm using an M20 starter with 2 posts, I used both small (solenoid and power) wires from the M50 starter on the small post and the big-ass red wire from the alternator on the large post.

The X20/C101 adaptor hasn't been made yet so that's not even an issue. I need this swap finished in the next few days, so please, put on your thinking cap/aluminum foil hats/whatever and throw some ideas at me. I'll probably be looking at ETMs for the rest of tonight and getting up early tomorrow.

[lifeiskaos]

What happens when it "shorts"? Wires roast?

Are you sure that you don't have a power wire grounded, or a power wire connected to power?

I'm a bit confused

Edit: What's the "starter ground"?

[Wh33lhop]

Big post on the starter gets grounded with the big main ground wire (the one that clamps on the ground post). The big starter post also gets connected to the big alternator post.

I mulled it over but I really don't see what I could have fucked up power/groundwise, unless it's somehow the above. The only connection to power is from the power distribution/fuse box (and presumably the fuel pump relay cluster).

It only shorts when I ground the engine block and the oil level sensor is plugged in, and only the ground wire from the oil level sensor roasts. I'm really hoping this is some stupid simple mistake I've made.

[gregslow318i]

pleas post of your current connections at the starter, they should not be any ground wire to the starter, the big outer most post on the starter(13 mm) is not a ground but the main (+) pwr lead from the bat, the top post(10mm) is the under-load. bottom post (8mm) is the starter signal from the switch....if you think about it the starter its self is grounded via the block and does not need another ground.

Big post on the starter gets grounded with the big main ground wire (the one that clamps on the ground post). The big starter post also gets connected to the big alternator post.

I mulled it over but I really don't see what I could have fucked up power/groundwise, unless it's somehow the above. The only connection to power is from the power distribution/fuse box (and presumably the fuel pump relay cluster).

It only shorts when I ground the engine block and the oil level sensor is plugged in, and only the ground wire from the oil level sensor roasts.

[lifeiskaos]

That's what I was thinking.

Maybe I'll have more input tomorrow. I'm effing tired.

Were you at dockweiler??

[Wh33lhop]

Alright, let's start with the basics here. At the risk of sounding absolutely retarded:

The wires from the battery that terminate on the passenger's side of the firewall (the huge one and the little one) are both power? I've just been assuming that the huge one is ground and the tiny one is power. Don't ask me why, this is really the first time I've dealt with automotive electrical stuff and I'm new to the whole battery-in-the-trunk thing.

So. As for the connections to the battery junction block (as it's called in the ETM, amirite?). The big wire that terminates in a clamp clamps onto the huge post in the junction block and runs to the big post (13mm) on the starter. Connected to the clamp end of that wire are the bigger diameter wire from the power distribution/fuse box and the engine harness lead (that exits the 318/M3 harness cover with the DME connector and relays). Connected to the smaller wire in the battery junction box is the smaller wire from the fuse box.

Now, why the hell do they have two different wires both with the same voltage coming from the battery?

[Wh33lhop]

pleas post of your current connections at the starter, they should not be any ground wire to the starter, the big outer most post on the starter(13 mm) is not a ground but the main (+) pwr lead from the bat, the top post(10mm) is the under-load. bottom post (8mm) is the starter signal from the switch....if you think about it the starter its self is grounded via the block and does not need another ground.

I'm using the M20 starter, with both smaller wires (that would go on the 10 and 8mm posts on the M50 starter) on the smaller (10mm I believe) post.

[Wh33lhop]

That's what I was thinking.

Maybe I'll have more input tomorrow. I'm effing tired.

Were you at dockweiler??

No working E30 = not at dockweiler. I'll most likely attend as "the guy who thought power was ground" when I've got a thirty to bring around. ;)

Thanks for the help, both of you--much appreciated. I just want to finish this damn car so I can drive it again.

[gregslow318i]

when I do the conversions I remove the m50 power wires that go through the harness, I think they get in the way and over complicate it.

I use the stock m20 starter wire (0-1 gauge) from the junction block to the outer 13mm post, then a 2 gauge wire from the same (13mm) post on the starter to the (13mm) at the alt. and its done just 2 wires.

also the 2 leads that come out form the fuse bock are both (+) leads dont ask me why bmw made the black and look just like grounds...

[Wh33lhop]

when I do the conversions I remove the m50 power wires that go through the harness, I think they get in the way and over complicate it.

Which wires exactly do you mean, and how do you remove them? I figure power wires are pretty necessary for the operation of the engine and sensors, are they not?

I use the stock m20 starter wire (0-1 gauge) from the junction block to the outer 13mm post, then a 2 gauge wire from the same (13mm) post on the starter to the (13mm) at the alt. and its done just 2 wires.

Doesn't the starter need a signal wire too?

also the 2 leads that come out form the fuse bock are both (+) leads dont ask me why bmw made the black and look just like grounds...

Ugh. What the hell...

[MattM]

i had the exact same problem when i first went to run mine, the ground wire for the oil level sensor fried... it was something in my connector i had connectd wrong, recheck you adapter and make sureeverything is right, if you followed some guys post online on how to wire it, check the etm or another source to double check. this was my mistake, someone gave me the pinout wrong.

here is my post:

http://www.r3vlimited.com/board/showthread.php?t=143712

[Wh33lhop]

i had the exact same problem when i first went to run mine, the ground wire for the oil level sensor fried... it was something in my connector i had connectd wrong, recheck you adapter and make sureeverything is right, if you followed some guys post online on how to wire it, check the etm or another source to double check. this was my mistake, someone gave me the pinout wrong.

here is my post:
http://www.r3vlimited.com/board/showthread.php?t=143712

Thanks for the suggestion, but I haven't even hooked up the X20/C101 yet.
i think this is just a coincidence.

HOWEVER, is the second oil level sensor wire (the brown/yellow one) really supposed to be ground? I've got it hooked up to power through the big harness lead...

[Wh33lhop]

Disregarding the wire clutter, is this right? I removed the lead from the engine harness as I'm not sure if it's really meant to be connected to power:



Throw me a bone guys, I know it's a lot to read, but I need this swap done yesterday. Thanks again.

[Spaz]

Follow that lead back and if its connected to red or red/white it will go to the power lug.

If its connected to brown then it goes to the ground lug on ur strut tower.

DOUBLE/TRIPLE Check the wire colours.

-Cam

[Wh33lhop]

Will do, thanks. :)