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Old 11-14-2017, 08:54 PM   #1
Slimssousa
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Question Alternator wonít turn on -

My alternator doesn’t turn on during startup sometimes, so I have to jump it with a wire coming off the battery. Would there be a problem if I just constantly had that wire hooked up to the alternator that’s connected to the battery ? Or would it ruin the alternator by possibly giving it too much power? Help
Picture of wire that connects to alternator https://ibb.co/hHOmXm
Picture of wire that I use to kick on the alternator https://ibb.co/im1tdR
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Old 11-14-2017, 10:33 PM   #2
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Every automotive alternator that I have seen requires some form of field flashing to start generating voltage. Field flashing consists of applying a small voltage to the field winding to generate a small field current which then starts the alternator generating voltage. Once it is generating voltage it is able to internally supply the required field current through the voltage regulator. When you jump 12v to that connector, you are doing the field flash. Leave that permanently connected and the alternator will try to run at max output which can be over 16 volts - dead battery in short order

My old 1987 745 had a voltmeter and I can't remember the details of the field flashing circuit. If your 1991 has a charge indicator light, check to make sure that the charge indicator light is working. It is very common to use the small amount of current that flows through the indicator light bulb filament to flash the field. A burnt out bulb results in loss of field flashing.
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Old 11-14-2017, 10:44 PM   #3
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You won't overcharge. It's just the exciter wire to make it start charging. You will just lose the dummy light.
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Old 11-14-2017, 10:49 PM   #4
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I do have Burnt out taillights and I do get the bulb indicator, they’ve been out since I’ve had the car and this problems been going on since I’ve had the car I will look further into it and replace the bulbs as soon as I get a chance to, maybe that just might save me.
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Old 11-15-2017, 10:44 AM   #5
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From the home page:

http://www.turbobricks.com/maint.php?content=art0031


I suspect you don't have 12v on the exciter wire from a bad cluster or a burned out bulb.
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Old 11-15-2017, 06:11 PM   #6
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The thing is, sometimes the alternator works and sometimes it doesn’t. Lately it’s been happening a lot more than normal and I need to fix this problem because I want to drive it more.
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Old 11-15-2017, 06:56 PM   #7
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Welp....do you have 12v at the exciter wire always?

Does the charge light work???
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Old 11-15-2017, 06:59 PM   #8
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Quote:
Originally Posted by ZVOLV View Post
You won't overcharge. It's just the exciter wire to make it start charging. You will just lose the dummy light.
You are correct if he is jumping to the alternator D+/61 terminal. This will work if he uses switched power. If he uses a continuous un switched connection off the battery the alternator voltage regulator will remain permanently energized and since the battery voltage is below the regulation point that regulator will attempt to boost the voltage on a non running alternator likely draining the battery. Best solution is to fix the flash circuit which may just be a burnt out / loose bulb.

If he is flashing to the alternator Df terminal then he will most certainly cause high voltages with a permanent connection to the battery terminal. On alternators with integrated voltage regulators the Df terminal is sometimes brought out to the external case for testing purposes. It is typically a stud and capped with a plastic insulating cap with no permanent external connection.
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Old 11-15-2017, 07:05 PM   #9
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Quote:
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The thing is, sometimes the alternator works and sometimes it doesn’t. Lately it’s been happening a lot more than normal and I need to fix this problem because I want to drive it more.
If operation is hit and miss, you likely have a bad connection to the D+/61 (excitation) terminal. Sometime when the car is running / alternator is not working, pull the wire to the D+/61 terminal and measure the voltage on the wire (not the alternator). You should have 12v to ground. If not, you have a bad connection in that circuit. Best solution is to find the wiring diagram for the car and trace that wire back (likely to the instrument cluster) to find where the problem is.
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Old 11-15-2017, 07:13 PM   #10
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Originally Posted by ZVOLV View Post
Welp....do you have 12v at the exciter wire always?

Does the charge light work???
No I donít have the exciter wire connected to the alternator at all times because Iím afraid somethings gonna go wrong. I do connect the exciter wire when I know the alternator is not on, then I disconnect the wire when it turns on, and put the factory wire back on. I know when the alternator is not on because almost all the lights warning lights dim up on the dash.
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Old 11-15-2017, 07:36 PM   #11
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HAVE YOU CHECKED FOR 12V AT THE EXCITER WIRE?

Does you little battery light turn on in the cluster when you turn on the key? Kp2.


12V just needs to be "slapped" to the exciter once per drive. I drove with my cluster out on my 240 and had to remember to slap 12v to the correct pin ONCE, for just a moment, and the engine would noticeably rev up as the alt started charging.
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Old 11-15-2017, 09:43 PM   #12
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HAVE YOU CHECKED FOR 12V AT THE EXCITER WIRE?

Does you little battery light turn on in the cluster when you turn on the key? Kp2.


12V just needs to be "slapped" to the exciter once per drive. I drove with my cluster out on my 240 and had to remember to slap 12v to the correct pin ONCE, for just a moment, and the engine would noticeably rev up as the alt started charging.
I read your previous thread wrong, 12v is at the exciter wire sometimes, and thatís when the alternator is able to turn on. No the battery light doesnt come on when the alternator is on. But when the alternator decides not to work multiple lights are on including the battery light.
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Old 11-16-2017, 02:06 PM   #13
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Does the battery light turn on when you turn the ignition to the on position???!!!!!!
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Old 11-16-2017, 02:40 PM   #14
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Calm down, Zach. A true Master Jedi Tech excercises patience.


OT: Regulator on its way out, probably. Does it self excite when you rev it to cca 4k rpm?
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Old 11-16-2017, 03:18 PM   #15
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Quote:
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Does the battery light turn on when you turn the ignition to the on position???!!!!!!
When the alternator works, no the battery light doesnít turn on. When the alternator doesnít work all dash lights light up, including the battery light.
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Old 11-16-2017, 03:55 PM   #16
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Quote:
Originally Posted by nordmaschine View Post
Calm down, Zach. A true Master Jedi Tech excercises patience.


OT: Regulator on its way out, probably. Does it self excite when you rev it to cca 4k rpm?
I’m not sure, but I’ll have to try later today when I get a chance.
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Old Yesterday, 03:08 AM   #17
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I thought that generation 7/9 series had an instrument cluster flexible circuit board that was commonly bad and caused this problem. I know I had it on one of my 940s. I had to check when I turned the key that the charge warning light came on. If it didn't, I had to smack the dashboard until it did, otherwise I'd drive with no alternator and run the battery down. Eventually I replaced the circuit board and never had another problem.

Watch for that dash light before you start the car.
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Old Yesterday, 10:10 AM   #18
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Key on, engine off, does the charge light illuminate?
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Old Yesterday, 11:43 AM   #19
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Quote:
Originally Posted by ZVOLV View Post
Key on, engine off, does the charge light illuminate?
No.
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Old Yesterday, 11:47 AM   #20
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Quote:
Originally Posted by LloydDobler View Post
I thought that generation 7/9 series had an instrument cluster flexible circuit board that was commonly bad and caused this problem. I know I had it on one of my 940s. I had to check when I turned the key that the charge warning light came on. If it didn't, I had to smack the dashboard until it did, otherwise I'd drive with no alternator and run the battery down. Eventually I replaced the circuit board and never had another problem.

Watch for that dash light before you start the car.
I’m almost sure that this problem is coming from the cluster. Possibly a bad soulder. It’s very finicky. The alternator only works half the time.

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Old Yesterday, 02:44 PM   #21
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My 940 has the same problem. Alternator does not come on when I start. When I bought the car from previous owner, he said the cluster has a cold solder joint.

PO had a button installed next to the light switch to get the alternator started. Not too sure about wiring, but I think it's just the 12v from battery to alternator through the button which closes the circuit when pressed. I just press it after I start the car and the alternator starts right up.

I guess it's the same go around that you are doing, just with a button and more conveniently placed The car has had the button for years, so I don't think there is a problem doing this.
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Old Yesterday, 02:55 PM   #22
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Quote:
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Iím almost sure that this problem is coming from the cluster. Possibly a bad soulder. Itís very finicky. The alternator only works half the time.
I had this problem with my 91 945.it was a bad soulder going to the charge bulb.i got lucky as my coworker at the time was the lead mechanic and electronics guy for a private jet.it took him 5 minutes to find and repair.wish you were closer,I'd loan you mine to see it's that's your problem,I suspect it is.
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Old Yesterday, 02:58 PM   #23
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My 240 has been very flaky as well. The alt light doesn't come on with the key on, engine off, and I know it should. The alternator charging is also hit or miss, fairly flaky.

I spent a while trying to verify that I had it wired correctly a couple of weeks ago (before getting sidetracked ina bathroom remodel project, lol). Because a couple of years ago I rewired 95% of the engine compartment when I went to MS3X, got rid of a bunch of unneeded stock wiring, added some new wiring, etc.

And verified that I did indeed have it wired correctly, and I did indeed have 12V+ at the exciter wire when the key was on (checked with a multimeter), but as far as I could tell, it was an *extremely* low amperage 12V+. Enough to read 12V when unplugged, but not enough to actually energize the alternator.

I tried grounding the wire, because per the wiring diagram, it's fed through the alternator warning light, so it's not a short circuit. And instead of lighting up the alt warning light like it should have, various other lights lit up (ABS, SRS, upshift? can't exactly recall), but not the alt warning light. The wiring diagram shows a sort of confused mess with all of those things hooked together, presumably with a bulb burned out that could happen? I took the cluster out, but the bulb looked good. I swapped it for a KNOWN good bulb and put it back in the car, and got the same exact symptoms. That lead me to do some Googling and I found this thread, regarding burnt/failed/whatever pathways in the gauge cluster itself: http://forums.turbobricks.com/showthread.php?t=279601

I haven't had a chance to take the cluster back out and check, but I gather that is probably the problem. Path through the alt light is failed in some manner, so I'm just getting some trace amount of current backtracking through the other lights, not enough to reliably light off the alternator.

Older, well used alternators with lots of miles build up some residual magnetism in the field coils, even if they aren't energized externally they can self-excite (HEEEEEEYYYY-oh!) and start charging if they're spun fast enough.
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Old Yesterday, 06:40 PM   #24
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Thanks for the info y'all, will be definitely checking out the cluster later today. im knee deep in your guys' info right now lol. pray for me!
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Old Yesterday, 08:03 PM   #25
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7th
Quote:
Originally Posted by ZVOLV View Post
Key on, engine off, does the charge light illuminate?


Quote:
Originally Posted by Slimssousa View Post
No.
You have found your problem! Either a bad bulb, or cluster circuit board issue.


Just to make sure, turn the key on, remove the exciter wire and put a test light, not a meter, between the terminal and ground. Make sure there truly is no voltage/current there and not just an open ground.

The ground wire for the alt also fails commonly. Inspect the crimps closely.
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