New alternator not charging!

TerryBPP · 10-20-2003, 05:17 AM

I hooked up my new alternator and its not charging. Can anyone tell me if its hooked up correctly? I did not hook up the black wire because the directions told me it was the ground for the external regulator.

Help!!!!

304065 · 10-20-2003, 05:41 AM

OK, you converted from an externally regulated alternator to an internally regulated alternator, right?

Did you locate the Porsche service letter, originally posted by Warren, that provides guidance for how to do this?

It looks like you hooked up the wires correctly. Basically, any brown wire in your car is a ground, so that and the ground strap to the top of the case can be connected together. The B+ wire runs both to the 12-pin plug and down to the starter. And the all-important D+/61 blue wire looks right. Let me ask you this, when you turn on the ignition and touch the blue wire to ground, does the warning lamp turn on?

304065 · 10-20-2003, 05:50 AM

Alternator Install

TerryBPP · 10-20-2003, 05:54 AM

No the light doesn't come on but I the gauge is fried so who knows. The Tech letter showed a completely different style alternator than the one I had or istalled. Also I hooked the ground strap to a different D- than the 2 brown wires. Do you think that would make a difference?

TerryBPP · 10-20-2003, 06:12 AM

Here is my old one and the new one. As you can see, my old one looks nothing like the one on the bulletin.

304065 · 10-20-2003, 06:57 AM

If the light doesn't come on when the blue wire is shorted to ground, your alternator will never charge. This is your problem.

Disconnect your battery

Take a butter knife and put a piece of duct tape on the blade

Carefully pry out the oil pressure gauge with the knife

Verify that you have a blue wire going into one side of the bulb holder for the alternator warning light, and a red wire with black stripe into the other side (switched +12v)

Verify that the bulb is good. It should be a 2w bulb, you really need 4w but we can cover that later

You have to have this working. Check everything if you don't, that is, put your voltmeter on the red/black wire going to the bulb holder to verify you have 12v with the igniton turned on. check the continuity of the blue wire all the way back to where it connects to the alternator- with your voltmeter on the ohm scale, with one probe on the blue wire that connects to the warning light, and the other probe on the connection to the alternator (you may have to rig up a very long jumper to test this) you should get zero ohms, or pretty close to that.

The way it works is, current flows out of the battery through the ignition switch, through the bulb, into the blue wire, and into the alternator field, where it magnetizes the rotor. The rotor begins to turn, and this magnetic field induces a current in the stator windings which is rectified by the alternator diodes and fed back into the rotor by the voltage regulator. Once that happens, the potential difference between both sides of the warning light drops to zero and the light goes out.

Without the blue wire and warning light, the alternator will never start charging.

Good luck!

TerryBPP · 10-20-2003, 07:13 AM

I will check it but the strange thing is that the bulb didn't work for the last eight months and the car ran fine. Weird. Thanks for the help. Do you think having the Ground strap and the brown wires on different D-'s could be bad?

304065 · 10-20-2003, 08:21 AM

Re: the ground strap and the brown wires, absolutely not a problem, no way.

If the light didn't work, it might be bypassed.

cstreit · cstreit's Garage

That bulb is responsible for setting the initial field or 'bootstrapping' the alternator. If it is not there, or not working, then your alternator will not start.

TerryBPP · 10-20-2003, 09:23 AM

So I assume my old alternator already had a internal regulator?

304065 · 10-20-2003, 09:56 AM

Terry:

Looking at the picture of your old alternator, it's clearly an EXTERNALLY regulated one. You can tell because it doesn't have a voltage regulator mounted at the bottom, and also because it has a terminal marked "DF" or Dynamo Field, which is where the black wire from the external regulator connects.

The purpose of the bulb is to generate the correct level of current flow in the D+/61 "blue wire" circuit. If there's no complete circuit, the alternator won't "bootstrap" and begin charging. If you bypass the bulb and don't have a load, you effectively have a short-circuit to ground (the VR shorts the field to ground initially) so that the only load in the circuit is the field windings. That's probably the reason your old alternator went bad.

Where the regulator is located really doesn't matter from an electrical point of view. I have found, however, that having the VR at the bottom of the alternator, located only 2" from the engine case, makes it vulnerable to "heat-soak"- over the winter I plan to convert back to the old style, externally regulated type.

Anyway, here's what you need to do:

1. Fix the oil pressure gauge- get yourself a bulb holder and make the correct connections behind the dash.

2. Verify that when you touch the blue wire (all the way back where it connects to the alternator) to the engine case, the warning light comes on.

3. Put everything back carefully and try it. Be sure to have a fire extinguisher handy. I'm not kidding, if you hook it up backwards by mistake it might do all kinds of bad things like catch fire or explode your battery.

4. Once it's working, you may find that you need to install a 68-ohm, 10W rated resistor in PARALLEL with the bulb contacts. This is to increase the current flow through the blue wire circuit to allow the alternator to "bootstrap" itself at idle. If you don't do thiat (like me) then you will start the engine off the battery, and have to raise the revs to about 2000 for the alternator to begin charging. See Warrens' exhaustive articles on this in the archives.

Good luck!

TerryBPP · 10-20-2003, 10:26 AM

Thats the problem! I thought the conversion had already been done. I need to do that. Have you seen any better description of this conversion? The tech bulletin doesn't help much.

TerryBPP · 10-20-2003, 10:45 AM

Never mind thats not the problem. From what I have read in the archives the external regulator can be left on there. Right?

304065 · 10-20-2003, 12:48 PM

It doesn't get any better than the factory sheet.

Remove the external VR from the plug.

Cut the DF wire off flush with the wiring harness and tape it over. You don't need it.

That's it. The blue wire and brown wires go to the plug and right back out again. You arent' changing anything in the circuit except the DF wire.

No matter what you do, that blue wire has to turn on the lamp when shorted to ground.

TerryBPP · 10-20-2003, 01:36 PM

i got home and checked for the exteral vr. it wasn't there! how is it possible to have the alternator i had and no vr?

304065 · 10-20-2003, 02:12 PM

It's not possible. Without a voltage regulator somewhere in your car, your alternator would fry itself in seconds.

You should get a flashlight and find out what the PO did.

TerryBPP · 10-22-2003, 04:51 AM

Is this the way it should be hooked up?

304065 · 10-22-2003, 05:18 AM

Just for grins, here's how the factory shows it:

TerryBPP · 10-22-2003, 05:43 AM

I have 2 blue wires. The red and the black is there though.

304065 · 10-22-2003, 05:58 AM

Terry,

Find out which blue wire is the one that connects to the alternator in the back. Put your multimeter on the end up front, and the other probe on the terminal that connects to the alternator. You may have to use a long jumper wire to do this. If it reads zero ohms, that's the one you want.

The red wire with black stripe should "daisy-chain" across the back of the other gauges. It comes out of the ignition switch and starts on the back of the fuel gauge, then to the oil pressure gauge, then over to the other gauges.

You should connect that wire to one terminal of the bulb holder, and the blue wire to the other terminal.

BEFORE you put power to it, please make sure you don't have any loose wires just hanging out behind the gauges. If there are connectors that aren't hooked up to anything, put some electrical tape over them. In particular, you should make sure the black wire with blue stripe that powers the gauge lights is properly connected, and insulated if it's not. A bunch of people have FRIED their wires and started fires behind the dash becasue of this-- me included! the reason I know so much about the wiring of 911's behind the gauges is because when I went to fix my alternator, I turned the power on and the red wire with black stripe shorted against the brown ground wire, and MELTED to it in about four places. So I made new ones from scratch!

Not trying to scare you, just save you trouble.