m50 power wiring, need assistance

[Rocla]

k i know the electrical 'thunk' you're talking about. it could be the starter barely turning over.

Actually solenoid going on and off. When the solenoid feeds power to startermotor, voltage will drop dramaticly as starter tries to revolver. When voltage drops near to zero due dead battery solenoid will loose the contact and disconnect power from starter. After solenoid relases power from starter voltage will raise slighty, just enough to pull solenoid enaged again and cycle will start over again.

Result will sound like klick, klick, drrrrrrrrrrrrrr.

Sorry, I can't simulate sounds in english, in my language it would be

klok, klok päärrrrrrrrrrrr :)

Edit: you might try to jump it, if result is same, try jumping it with your negative battery cable removed from battery. That includes a small risk of damaging electronics of your car. I've done it like 100 times without any damage, but there is as risk.

[hugh jass]

it really sounds like a dead battery to me. old batteries won't hold much of a charge. the easiest thing would be to take it to autozone where they can load test it for you for free.
i think i know the electrical 'thunk' you're talking about. it could be the starter barely turning over.
sorry if i sound like the others, but its always easiest to 100% eliminate the stupid things first.

[LooN]

1 bad cell did that to me.

Even being jumped by another car.

Car would barely crank, then couldn't even do that.

Make sure you can turn over the car by hand though, you could have the same problem as me. The flywheel was resting on the back of the block and couldn't move.

I need to make something clear...not sure if people aren't reading or it doesnt matter, but when I turn the key to start position there is a VERY LOUD electrical-sounding *THUNK* (I can actually feel the whole car jerk) and ALL the lights in the car go OUT, except the speedometer and tach which go VERY dim. After a very precise delay (its the same every time), about half a second, there is a loud *CLICK* and everything turns on again. Forgive me if I'm a little scared of testing any voltages with the key in the "start" position when this is the case.

Before I replaced the wiring harness, the engine would crank STRONG and easy with the same battery and starter I am using now. I will test it with another battery tonight just to be sure, but I dont think the battery is the problem.

Have you check the outputs off of the main relay with the key in start position? What are the voltages?

What's the best way to do this? Sorry for being such a noobie, but it IS my forum title ;)

A tech at my work who used to work at BMW of Bellevue (and who has a very nice E30, btw) told me to "divide and conquer" in order to find where the harness is grounding in the place it shouldn't be. He told me to do this:
-Disconnect the battery, and make sure the two disconnected wires weren't touching anything.
-Take an ohmmeter and connect one end to an unpainted chassis point (ground).
-Beginning at the starter, touch the other end to positive leads on the harness.
He said that if everything was connected properly, I should have "infinite resistance" at the starter positive lead (I'm assuming because there should be no connection between the ground and the positive lead?). However, I do get a resistance reading...is this my problem? Or would I get a resistance reading if everything was connected correctly? Should it just have a really, really high resistance between these points?

What is the best way to go about using this technique to diagnose my problem (assuming that a positive lead on the harness somewhere is grounded where it shouldn't be, and the battery is good)??

Thank you SO MUCH EVERYONE for all your help so far. I apologize for being such a pain. I just want my Ultimate Driving Machine to actually see some pavement. :D

LooN

P.S. if it makes a difference, this is a '92 non-vanos E36 body with a '95 vanos M50 motor

[Mike B.]

Have you check the outputs off of the main relay with the key in start position? What are the voltages?

[DEV0 E30]

that's another thing i was thinking about checking, would a battery with a bad cell still provide adequate power to turn on everything else, just not crank?

1 bad cell did that to me.

Even being jumped by another car.

Car would barely crank, then couldn't even do that.

Make sure you can turn over the car by hand though, you could have the same problem as me. The flywheel was resting on the back of the block and couldn't move.

[LooN]

that's another thing i was thinking about checking, would a battery with a bad cell still provide adequate power to turn on everything else, just not crank?

[DEV0 E30]

I had a dead cell in my battery, get it tested.

Try to manually turn over the engine by hand. 22MM wrench on the front, remove radiator for ease.

[LooN]

cahomey i already did that 3 days ago, thats no longer my question/problem

[cahomey]

we JUST went through this tonight ourselves... on that A/B pic stuff: slit the jacket open and peek in... red = go to power distro block, black/brown = ground that thing. check that out.

[LooN]

I think your battery is dead.

100% charged, left it on last night and all day today, all the lights in the car are extra bright now. still does the same thing :(

Any chance you forgot to ground the engine block? The right side motor mount to the ground point on the frame rail is good location.

just checked, engine block is grounded

I think you're shorting something out at the starter. When you move the key to the "start" position, the primary thing that happens is +12 getting applied to the black/yellow wire. Maybe the black/yellow wire is connected to a ground point on the starter? Or, maybe the starter is bad and shorting it's +12 wire to ground via the solenoid?

How possible is this? That the starter is bad and its shorting its +12 wire to ground via the solenoid? Happened to anyone before? At this point I think its a possibility because after checking a ZILLION times, I'm 99.99% sure all my wiring is correct.

Everything turns on and works when key is in the "on" position. When I turn it to "start" position, there is a loud KACHUNK as all the electricity grounds to the chassis (that is what's happening, as far as I can tell). Everything goes dim for about a half second, then *CLICK* everything goes on again. The delay is very precise--could it be a relay of some sort??

ARe there any fuses in the car besides the fusebox? I heard the main lead from the battery has two wires--one thick, one thin, and that the thin one is fused. WHere is it fused? THe wires disappear behind the upholstery in my trunk.

Thanks everyone for all your help so far!!

LooN

[equate975]

I had the exact same thing happen to me. Now I dont feel to bad lol.

I wish I knew what I did to fix it though :(

Auctually, I think I was just a dumb ass and mixed up the positive and neagtive wires, because I shot sparks all over the place. Somehow didnt do any damage.

[clavinZERO]

we JUST went through this tonight ourselves... on that A/B pic stuff: slit the jacket open and peek in... red = go to power distro block, black/brown = ground that thing. check that out.

[Brew]

Any chance you forgot to ground the engine block? The right side motor mount to the ground point on the frame rail is good location.

[matt]

I think your battery is dead.

[LooN]

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