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tii Alternator / Electrical Puzzler - Solved and a Lesson


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It is with great humility that I submit this post.  Here’s the punch line:  The black plug on the back of the alternator houses three wires.  The plug can be seated in the alternator, with the metal clip in place, but the wires can still not be pushed all the way onto the spades on the alternator.  That is what happened here, with I think some additional excitement thrown in.  Car is a ’72 tii.  Here’s the specifics:


New Bosch rebuilt alternator and ground strap go in a few months ago.  All is well.  Drive for a few hundred miles without incident. 


One day, I start it (this is the day before an RGB event) and hear a new sound – a soft whiring under the hood.  Alternator bearing?  Water pump?  I wasn’t sure.  It moved with the RPMs of the engine, it sounded like.  It was definitely a new sound.  More issues materialized:


-“L” charging light began to faintly glow at idle.


-Measuring with the multimeter at the battery, I see the alternator is not quite putting out enough volts at idle, but is better at higher rpm.


-Also when turning on accessories, the alternator doesn’t keep up – volts go down, but don’t come back up until the accessories are turned off.  All accessories work normally, however.  


-Idle speed was lower, though I thought it was unrelated.  My only thought was maybe the bearing sound I thought I was hearing meant there was a bit more drag on the engine at idle?  Wasn’t sure if that was possible.  Again, figured it was unrelated. 


- Wiring on alt looked good – nothing hanging off.  Pressed the plug in; it was in. 


Figured alternator was going bad, and decided to run with it until it dies.  Figured I was another victim of the bad Bosch rebuilds.  I would just drive with my $5 cigarette lighter voltage gauge, to keep an eye on things. 


Then on Sunday AM on the highway (going to another RGB event)…”L” light starts flickering at high rpm – volts start varying a lot when flickering…this is all new.  Saw a high of over 16 volts on the gauge, and quickly pulled the plug on the rest of the trip – worried about too much voltage for hours of driving could be really harmful to the battery and electrics in general.  I had driven about 25 miles. 


I think to myself, that flickering light – seems like a loose connection, even though the flickering was not connected to going over bumps.  But you’d swear it was a loose connection by the strobe-like flashing the “L” light was doing constantly, when at speed. 


Once at home, I saw that, while the black plug on the back of the alternator was in, and the clip in place over it, on the back of the alt, the green wire was not really pushed all the way on the alt’s spade.  AND the rear most part of the green wire’s connector was touching the metal clip – right up against it.  I had to be under the car (and alternator) to really see this (tiis are so much fun sometimes). 


I pushed all three wires that are in that black plug back on as far as they would go.  Put the battery back in, connected it, and started the car.


Faint glowing “L” light at idle is gone.  Whiring sound is gone.  More volts at idle, and very steady voltage reading when driving – voltage hardly varies at all.  Turn on accessories, and volts do not vary.  The charging system is now working exactly the way it is supposed to. 


Idle speed is higher, too, I THINK – the temperature was in the thirties on Sunday and I only drove the car for 15 mins after it was fixed – I’m not certain it was 100% warmed up on that drive.  I’ll drive it on a warmer day and check that.  Again, it could be unrelated.  But maybe one of you knows if it is, or isn’t. 



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