Alternator regulator issues 71 911t

[Mauireman]

Im stumped and need help. I’ve been working on this car for 10yr and just about ready to put it on the road but I’m having a real problem with, the Alternator Regulater Dash light.

When I connect the battery I get a slight spark with the ignition OFF. I’ve tracked it down to the blue wire going to D+/61 terminal on the votage regulator, it has battery votage and the Alternator light on the dash is on with the ignition OFF. If I turn the ignition ON the blue D+ wire still 12v and the alternator light goes OUT and the Oil light comes on.

I’ve check the Bosch Alternator wiring connections and they are correct, the alternator has been rebuilt and a new Hella regulator is installed. If I disconnect the blue wire at the dash alternator light, the Blue D+ wire going to the regulator still has votage?


I would GREATLY APPRECIATE any idea or suggestions! I want to get this car on the road!
Thanks
Dan

[304065]

What do you mean a slight spark? Between what and what?

If alt light is ON with ignition OFF you either have it wired wrong or you have a shorted out diode in the alternator.

Please explain in detail how you connected the wires to the alternator, what color to where. And a photo of the back of the gauges would help.

[Mauireman]

Thanks for the reply! The slight spark is at the battery when I connect it.
I’m checking the wiring today, I suspect it’s the problem is in the wiring harness as I did have to do a lot of re-wiring, a lot of the engine compartment wiring and fuse panels were fried when I got the car. I’m starting by tracing the blue wire connected to the regulator back to find our were the voltage is coming from, I suspect it’s somewhere between the regulator and the alternator? I’ll keep you posted and send a photo of the alternator if I get that far before finding the problem.
Dan

[Mauireman]

The voltage is coming FROM the D+ terminal on the alternator with only the B+ lead connected? So as you said before, this means a diode is shorted out? If so I guess it’s back to the alternator shop?

[304065]

Yes, bad diode.



D+/61 is the output from the "Trio" diodes which is connected to the VR and also to the blue wire to the warning lamp. In normal operation, with the engine not running and key on, current flows from the battery, into the ignition switch, over to the bulb holder in the oil pressure gauge, through the bulb filament (lighting it), back to D+/61 where it can't go through the diodes, over to the VR where the VR senses that the voltage on D+/61 is LESS than the set-point voltage (lets call it 14.4V) so the VR sends current to the rotor (through DF), energizing it like an electromagnet, then to ground.

The engine starts, the current in the rotor induces a current in the stator which is rectified by the main diodes and sent to the battery through B+. Also, voltage on the stator passes through the "Trio" diodes to D+/61 terminal, where its voltage balances the voltage flowing from the bulb holder. Since the voltage is the same on both sides of the bulb no current can flow and the bulb goes OUT.

In your case, the engine is obviously OFF, so voltage is flowing from the battery, into B+ across the main diodes (which it should not do) into the stator and then appearing on D+/61, flowing through your test lamp bulb to ground. Therefore, shorted main diodes.

[Mauireman]

THANK YOU! I’m off to Alternator shop tomorrow!

[Mauireman]

Does anyone have a suggestion as to where I can get diodes for my Bosch 0 120 400 725 Alternator? Or, should I switch to another type of alternator and how difficult would that be? I’m assuming the alternator shop that did the first rebuild doesn’t have the correct diodes, I’m on my way their today
Thanks Dan

[30westrob]

Napa stores and napaonline have a good selection.
Rob

[Mauireman]

Thanks for all the help from everyone! My alternator had 6 shorted out diodes! It’s back in my car and seems to be working fine!

[edmayo]

Must have been a reverse battery connection once.