m50 power wiring, need assistance

[LooN]

I ran a voltmeter test on the main power terminal on the starter--the one with the fatty red wires that connect to the power distribution block and the alternator. With ignition in the "off" position, it read about 12.7v, and in the "on" position, dropped to about 12.4v. However, when I turned the key to the "start" position, the voltage dropped to 5 volts. I'm pretty sure that's not enough to engage the starter, which explains why it isn't turning.

I have ruled out the starter and the battery as problems, and all I've changed is the wiring harness (before that, the car cranked easily).

So my questions are:
-Where could this extra current be going to?
-When the ignition is turned to the "on" position, does anything else happen besides +12v being applied to the yellow/black wire on the starter?
-Could a faulty relay be the problem?
-Could a faulty alternator or alternator connection be the problem?

Thanks for all your help guys...slowly narrowing this down.

LooN

[Brew]

I'm going to guess that the "fusible link" of your main power cable from the battery to the engine bay is smoked. Before replacing anything though, you need to make sure that there are no shorts (which is what killed it in the first place). Triple check all of the power and ground connections of the engine harness.

[Rev Engineer]

Is your intake manifold off? If not, I'd take it off to get good access to the starter. Next get a jumper wire, or carefully use a screwdriver to short the yellow/black terminal on the starter to +12 (do this with the wire disconnected). This will let you confirm the starter operation independant of the rest of the wiring. If you get a huge spark or something bad happens, you know where the problem is at - starter iteslf or the big red wire. If the starter spins normally, you're back at looking deeper into the harness, but you know that the battery is good, the starter is good, and that the motor can spin.

Starter operation with and without the key were the last things I checked before putting the manifold on and taking the car for it's first test spin.

As for the yellow/black wire, I think it also goes to some unloader relays that switch off accessories when the starter is being engaged. In the engine harness, I'm pretty sure it only goes to the starter. Here's another idea - try engaged the starter with the engine harness disconnected.

[LooN]

I'm going to guess that the "fusible link" of your main power cable from the battery to the engine bay is smoked.

Where is the fuse for this link? I suspected this but I can't seem to find it..the thin wire from the positive battery terminal disappears into the trunk upholstery..

Here's another idea - try engaged the starter with the engine harness disconnected.

Disconnected from where? By jumping those two terminals or by the ignition? The other night while messing around I tried turning the ignition to "start" position and nothing happened...took me a few minutes to realize my x20 was disconnected
And yes, manifold is off, not putting this thing back together before the starter engages

[BDSax]

Fusable link is in the trunk. just follow the thin wire and you will see it. its a flat piece with heat shrink on it. i think iots less then $20 at the dealer. alot of people just put car amp fuses on it and then your done. i think its a 30amp, but i may be wrong.

[Rev Engineer]

I ment the x20. If nothing happened with this disconnected, I'd still focus on the starter. It's pretty easy to manually short the starter to get it going. If I recall correctly, there are two smaller terminals on the starter. You need to be connected to the right one - have you gone over this issue? I think if the yellow/black wire is connected to the wrong terminal, you'll get a short. I'm sure this has been discussed somewhere on this forum.

Just do this:

remove the yellow/black wire from the starter - get a jumper wire and short the big red wire to one of the terminals on the starter. One of them should let the starter turn. I don't see any need to do anything else until you can confirm that you can manually crank the starter without the key.

[LooN]

Okay so I tried shorting the starter with a large screwdriver--main power terminal and the yellow/black wire terminal--and each time I did it, sparks flew and it melted spots on my screwdriver. I could hear loud CLUNK of the solenoid engaging, but the starter wouldn't turn. As far as I can tell, it's doing the same thing when I short it as when I use the ignition.

I know the starter is good because I just replaced it with a remanufactured Bavarian one..I think the problem is that not enough current is getting through the big red wire from the battery, because of the results of my voltmeter test (12.6v dropped to 5v when key moved to 'start' position). What wouuld cause this is completely beyond me...bleh... any more ideas?

[Rev Engineer]

You did try turning the motor by hand?? I think the starter is jammed. If you're getting a huge spark, there's enough current. I really don't think this is a voltage/wire problem. If it we're me, I might go through the effort of removing the starter and checking it outside the car. BTW - Which starter is it? You do know that you can't mix a e36 starter with a e30 flywheel?

There are a few terminal connections on the starter. One if a short wire that goes from the solinoid to the motor. You should be able to bypass the solinoid and apply power directly to the motor. This should spin the starter gear without the solinoid engaged.

Again, since you're getting a huge spark and nearly welding the screwdriver, the battery and the big red wire are supplying enough current. It's the large amount of current that the starter is drawing which drops the battery voltage. If the big red wire wasn't supplying enough current, than the voltage would never drop so low. I still think this is a starter issue.

[LooN]

Thanks for sticking with me Rev, you're the best :)

The car is a non-vanos E36, just putting a vanos motor in it, so no issues with flywheel incompatibility.

You've got me convinced its a mechanical issue; the starter that was there before the wiring harness swap worked great and the replacement starter is remanufactured, fresh from Bavarian, so I dont think the starter itself is bad. The motor itself might be jammed..I tried turning the engine over by hand, and it turns clockwise (it's the bolt in the front that connects to the fan, right?) but only the belt that is connected to the alternator turns. It doesn't sound like the pistons are pumping, should they? What should I do/what should I look for to make sure the motor is turning over properly?

[tonytony]

nooooooo it's not the bolt in front of the fan........its the big huge bolt i think 22mm that is connected to the crank pulley directly under the fan. There should be some effort in cranking it by hand but not extreamly hard. You should take out the radiator to crank it by hand using a breaker bar or a 1/2in rachet or use a big adjustable/cresent wrench.