I went to gas up my Lumped Series 3 today and noticed that the voltage gauge was not reading.
Got back home and checked and of course the alternator was not charging.
Picked up the required tools and went to the auto parts store.
Removed the alternator and had it tested and it passed.
Reinstalled alternator and with their hand held tester it said "Rectifier Failure"
Since it was under waranty, they replaced it. Tested in store "Passed". Tested on car "Rectifier Failure"
Removed from car and installed another. Tested in store "Passed". Tested on car "Rectifier Failure"
Removed from car and installed another. Tested in store "Passed". Tested on car "Rectifier Failure"
That's 4 alternators doing the same thing.
Since all 4 were remanufactured, the Store Manager is getting me a Brand New AC/Delco Alternator tomorrow morning.
When I start the car the Charging light goes "off" and at idle the alternators read Battery Voltage 12.45 volts. If I accelerate to 2000 RPM the 4 alternators output goes up to 13+ volts.
In the meantime, Is there a voltage regulator or some other device on the OEM Jag wiring that may cause this?
Attached is a pic of how my alternator is wired
The green tie wrap does not mean anything. I had a wire tapped there to activate my DRL relay. I removed it thinking that that was causing the 'no charge' issue

 

Which suggests that the alternator is not being 'excited' at low RPM

No.

However, the original section of wiring from the alternator to the "+" junction post on the firewall can become corroded underneath the insulation, causing grief. But, that wire might not even be in existence on your car


How/where is the wire from the dashboard light to the alternator wired in? I can't see from the picture. Resistance from the bulb is what 'excites' the alternator so it will charge at idle speeds. I don't think it was cause the rectifier problem that testing reveals.

Cheers
DD

 

On closer examination.....

If that brown/black stripe wire at the alternator goes to the warning light on the dash, you should be OK as far as that goes.

Cheers
DD

 

@ Doug: Yes the Brown/Black wire goes to the warning light on the dash. This wire is the original wire connected to the OEM harness which goes to the warning light.
2 days ago the alternator output was 14.3 volts
The warning light works and turns off as soon as I start the engine but the voltage output on all 4 alternators was 12+volts.
I am still using the OEM wire that goes from the alternator to the firewall on the driver(Left) side.

 

At minimum I'd check the connection at the firewall side. But I'd go further and disconnect it at both ends and check resistance. Over the years there have been stories of corrosion under the insulation. I came across this exact situation on a 1980 Series III belonging to a pal....after he had replaced the alternator several times. Sound familiar?

Cheers
DD

 

Thanks Doug. I will check and replace the wire from the alternator to the firewall. After all it is over 30 years old. I will post results afterwards.
Resistance reading 00.5 on the 200 scale. Since I don't know what the R reading should be, I am going to replace the cable anyway.

 

My .02 is that a new healthy alternaotor to firewall post will make things right.

I would suggest a good cleaning of that firewall post and the wires connected there.
Lots going on at that post.

Carl

 

Update: SUCCESS!!!!
I picked up the "BRAND NEW" alternator this morning. At the same time, I purchased 4 ft of #6 Marine Grade cable and 2 terminals.
I installed the new alternator and the 'no charge' issue was still there.
Based on Doug's advice, I made up a new cable from Alternator to Firewall and what do you know. The alternator started charging as it should.
At idle speed 13.9 volts
Acceleration increases the voltage to 14.56 volts.
@Doug:Thank you so much for your input.
I am now going to replace all of my old battery cables tomorrow.

 

Glad to hear you sorted it out,, I was watching the thread in case this would happen to me...as we have the same TBI set up. (350 700r4)
Happy for all concerned.. Doug has a pile of knowledge in his noggin and was a big help again...I always learn something from his posts.

 

Yessir! After the scenario with the 4 alternators, I was leaning towards some kind of wiring issue.
However, the alternator to firewall cable was furthest thing from my mind.
Kudos to Doug. When you know your stuff, you know your stuff.

 

Thanks, gents, for the kind words.

Cheers
DD

 

Yup!!!

Doug sure does earn his keep!!!

Carl