Mrmerlin

its quite possible your NEW alternator is failed,
whats the matter with the old one?

please post a picture of the brushes of both of the brush holders,
so we can see if the brushes being worn are your issue

IndyMatt

I have had the old one completely tested at the GOOD shop. Had it bench tested at Advanced Auto and it tested fine. Got the higher output unit thinking it might solve my issues, it hasn't obviously.

I will pull the Bosch brush holder and snap a picture. The no name one on the newer unit looks brand spanking new.

IndyMatt

Well got a new regulator and that didn't change a thing. The only thing that I changed before it was working to now was I did the water pump/timing belt. I had to remove the wiring harness to do the timing belt. I did not disconnect wires from the battery to the starter or from the starter to the alternator.

I still do not get the charge lamp with ignition on. This is the main issue, I think if I can get to where the charge lamp is illuminated in the on position then all will be well. The lamp lights up like a Christmas tree when the wire is grounded out. Everythign tests fine outside of installation, the exciter scircuit seems to be fine as the charge lamp lights up, the alternator tested fine, installed a new regulator with no change, battery is good. When installed and put in the car there is no charging and indicator lamp in the on position. I am at a loss with this one.

I am about losing it over this issue!

IndyMatt

Any ideas? Is there a ground or relay that I should check?

jon928se

The exciter circuit is clearly working, as far as the alternator. Hence it must be open circuit inside the alternator.

To confirm this first disconnect both leads (battery +ve and exciter) from the alternator otherwise you could blow up your meter. Then check the resistance (ohms) between the exciter connection on the alternator and ground (body of the alternator) if this is infinite ohms it proves the alternator has an internal disconnect.

You could also check this without a meter. Dis the exciter lead only, then connect a test lamp 12V parking light bulb or similar) between the Battery+ve terminal and exciter terminal. It should glow somewhat if the alternator is OK.

newworld

87s4 aut.

Just a quick jump in question on alternator....

I tested mine and I ignore the dash guage, but I was wondering what the s4 alternator should output.

On startup with nothing on...I get 13.6 or 13.7 v never goes to 14

With headlights on and AC on drops to 12.5 or so...

The dashboard usually reads 1 v lower .....when hot I have seen dashboard guage go as low as 11 which means I am at 12 v...with a lot of things on AC and headlights.... Etc

IndyMatt

It came out to be 3.4 ohms on the higher output unit and 4.6 ohms on the original. Both seem to check out fine.

IndyMatt

Dupe post.

IndyMatt

Dupe post.

IndyMatt

Here you go, dirty equals original.

Mrmerlin

Thanks for posting these pictures,
the Bosch part looks like the brushes are still in serviceable condition,

you could use the brushes from the other non marked unit for the Bosh part when the brushes wear out

Alan

I think this resistance seems way too high on both of these.

The charge lamp bulb resistance when on/hot is probably about 50ohms. The alternator exciter connection must not add too much additional resistance to this circuit if the bulb is ever to be lighted by the exciter supplying current to the rotor field the during the initiation process.

At 600+ ohms the current will be very limited - to a level too low to create the rotor initation field and also too low to illuminate the lamp.

V/R = I So ~12v/600 = 20mA (max) - you need more like 200-300mA to illuminate the bulb and create the field.

Your alternator doesn't work correctly (OR is designed for a quite different initiation mechanism than you have in a 928 - OR you measured it incorrectly).

What you describe is consistent with the results you have reported.

Alan

IndyMatt

Alan, that makes sense. A local 928'er has some spare alternators. I will grab one of those to test on my 928 and rerun the resistance test. I totally fubar'ed the original resistance testing. New one was 3.4 ohms the old one was 4.6 ohms. Not even sure how I screwed that up so bad. If you haven't noticed I totally suck at electrical, mechanical I am fine. I will grab our resident 928 owner/expert to do some wire tracing and testing.

Is there any trouble areas that we should hone in on first?

jon928se

Those resistances seem more the right sort of value.

Now I'm stumped.

Just a completely off the wall question for those that have experienced it. Is it possible that a defective ignition switch (electrical portion) could be causing this issue?

Alan

I'm not so sure you did screw it up - these higher resistance numbers would explain what you have seen... so I'd not be so quick to dismiss them.

Test again another 5 times - are the results inconsistent? try the alternators in varying orientations - something wierd going on here...

Alan