1973 Eldorado alternator issue

[JerRita]

Hi all I changed the alternator on my 73 eldorado and used an AC Delco rebuilt # 3342112A THe car charges at 14.3 but the GEN light is lit At a low idle it puts out 12.2 and the light goes out? I had no issue with the old alternator till it failed and the light worked fine.Everything is hooked correctly Does anyone have a clue what to check out Thanks PS I exchanged the alternator and it does the same thing? Thanks JeRita

[cadillacmike68]

12.2V seems to be too low, even at idle.  It should be about 13.1 with no load up to 14.5 or so with a load (lights, climate control on, etc.). Could be the internal regulator, or it's not wired correctly.

What is the RPM when you have the 14.3V?

["Cadillac Kid" Greg Surfas 15364]

Carefully check the plug in connector wires to be sure they are intact and making good connections.
Greg Surfas

[TJ Hopland]

I would take it to a parts store and have it tested.   These days 2 duds in a row seems pretty common.   The quality of the parts most places use is terrible as is their workmanship and quality control. 

You said the light is on when its reading 14.4 v?   Anything else not working or unusual happening in the car?  Do any other work recently?    Where are you reading the 14v?    Do you get the same voltage at the battery and say the lighter sockets inside the car?  The light lights when the alternators output voltage and the systems voltage are different so taking measurements from different places may give some clues.

[bcroe]

I am not so good with the mechanical regulator alts (mine was
converted), but that sort of thing can happen when a diode fails. 
Output will decrease, with that big gap in the 3 phase waveform
the voltage will average less.  The small diodes affect the light. 
Easy to see on a scope, not everyone has one.  good luck,
Bruce Roe

[bcroe]

I do not have a 73 book, what year did they go to the internal
electronic regulator?  Bruce Roe

[TJ Hopland]

73 was internal for sure.    Not sure when the change was had to be 71 or 72.

[bcroe]

73 was internal for sure.    Not sure when
the change was had to be 71 or 72.   

OK then what I said applies.  An open main rectifier diode will cause
gaps in the charging output, lower amps and lower ave voltage.  The
winding not delivering to the battery (thru the open diode) may spike
up in voltage in each cycle, which can start to light the light. 

An open smal diode (trio) will fail to continuously supply the rotor
current, and some current may be drawn thru the bulb.  Diodes
are not very hard to check, I do not change them on a rebuild.  Just
the bearings and brushes here, I have more faith in the original
semiconductors than in Asian copies. 

My 72 Chev book shows a mechanical V reg.  Bruce Roe

[J. Skelly]

I agree with Bruce.  I had the same problem on my '71 Eldorado.  The rebuilt/remanufactured alternators are not as good as a new one.  If the light glows on the dash, it is often the diodes.  I haven't owned my '71 in 32 years, but it took 2-3 to get a good rebuilt one w/o a diode problem or stripped threads for the mounting point on the housing.

As I recall, the integrated voltage regulator started with the '71 models.

[Roger Zimmermann]

As I recall, the integrated voltage regulator started with the '71 models.

yes, but only with the 80 amp. generator. The 42 and 63 amp. generator had an external regulator till 1972.

["Cadillac Kid" Greg Surfas 15364]

Not on the Eldo Roger.  They had internal regulator alternators starting in 1972.
Greg Surfas

[Roger Zimmermann]

That's true! I did not look at Eldo models.