strange problem
 

Does anyone know or heard of this:83 944
Car starts and runs with alternator belt disconnectd, when the belt is connected the car wont start?

Is the alternator wiring hooked up incorrectly? Did you do something to the car right before this started happening?

im not too familliar with the car, the wiring looks right but its not verified.
I cant say it ran correctly before because its was bought as a non running project. I got it to run finally, but when I installed the alt belt it wont run, remove it and it runs??????
My guess, bad alternator but just a guess.......

Maybe it was on too tight?

Only thing the belt does is drive the AC compressor & run the alternator. I would guess maybe the wiring isn't right.

the belt is tensioned correctly and the 2 wires going to the alternator look like they are in the right place.
the ac compressor turns free

The alternator is probably shorted and drawing current instead of producing it. (that's just a guess as that is a weird problem). I believe like you..the alternator is bad and causing this. If you need help finding one, let me know. Unhook the alternator wires and see if it still happens...my guess is that it will keep running.

You gurssed right, I pulled of the wire and it runs, off the battery of course. That makes sense, I may have a spare in the shed, I will try and swap it and see what happens.

this is getting silly: replaced the alternator- same problem!
I now determined that removing the small wire from the alternator(i think its the field wire) lets the car run, but the battery is probably not charging?!?!

Trace the wire. PO's do weird things. It could be going to ground or somewhere it's not suppossed to, cauing an electrical short.

Rich, you are correct. The small wire is the field wire, it sense load on the electrical system and will adjust the voltage regulator accordingly.

What kind of shape are the regulators in? Strange problem, really not sure what would cause it.

The regulator on the original looks good, its actually a rebuilt unit that was on the car, the replacement was from a good running car. After speaking with some engineers this morning, the first recommended polarizing the alternator(shows how old he is). In conversation the 2nd mentioned the ground path, which reminded me of the unholy alliance of ground wires at the rear of the cam tower, it seemed like way to many wires of heavy gauge convering at that point but at the time since the car ran (without the alternator belt connected) I didnt think it was a problem. Im betting that its a ground problem, I will have to check this later.
Thanks all for the input so far.

is there an alarm system on the car?

yes, factory alarm, why?

Alarm activated wont cause these issues.

wanderer- you maybe on to something, I traced the wiring and it seems the field wire on the alternator traces back to the alarm box. I am able to have the car run with the field wire connected by unpluging the factory alarm box. I found the factory alarm does have a seperate horn in the cowl but I dont fully understand the factory alarm wiring schematics, can someone shed some light on this?

The factory alarm uses the normal horn, doesn't have a seperate one.

I'm wondering if the PO didn't install an aftermarket one. Does the additional horn look like a regular car horn or something like this: http://cgi.ebay.com/12V-CAR-SIREN-HORN-SPEAKER-WARNING-ALARM-6-TONE-US_W0QQitemZ120229359476QQihZ002QQcategoryZ14932QQ ssPageNameZWDVWQQrdZ1QQcmdZViewItem

the factory alarm horn is located in the cowl area, its also indicated in the wiring schematics

just popped into my head, i know the alarm systems, especially the aftermarket ones can do some weird things. Let us know

Problem is gone! Turned out to be the alarm module! Very strange indeed!
Car is running with the belt and alternator wiring in place now and I am able to recreate the problem by reinstalling the bad module. There is alot of mystery about the wiring of the alarm and I will be going over the schematics with an electrical engineer in the coming weeks so he can explain it to me. It doesnt seem like the early schematics are very involved into the alarm system so I will look at the late car drawings to see if we can make sense out of it. If anyone has first hand knowledge of this system please save us some time.
Ok heres the deal: I unpugged the alarm module and the first thing I noticed when you turn the ignition key to the on position is that the alternator warning light does not turn on(first clue) when I try to crank the car it cranks but no fuel pressure. Install the good module and alt warning light comes on in the on position, cranks and builds pressure and starts. Next I arm the factory alarm and try to crank, alarm horn sounds, cranks no pressure no start. I disarm the factory alarm and same thing, this kind of threw me off but I had to remove the ignition key and reinstall it and it starts, this seems correct. Bottom line, the field wire travels to the alarm module and to the alt warning light, there was a short in the module preventing the car from running with the field wire connected. The bad module also intermittently disabled my fuel pressure probably thru the dme relay.

That is some good information to know Rich. Thanks for sharing. I haven't taken the time to figure out the alarm module either so when you do understand it, please share that as well.