Charging system question on 71

[willowbilly3]

 On my 71 Coupe Deville the Gen light stays on. I am getting 13+ volts at the battery when idling so it is obviously charging. My first thought is faulty regulator but I don't like just throwing parts at something hoping it's the fix. Is there a test I can do?

["Cadillac Kid" Greg Surfas 15364]

Is the "gen" light glowing faintly or is it bright?
Greg Surfas

[signart]

First test condition of your battery while not running. Should be 12.6-12.8v Check grounds, belt tension. Should have 14+ volts while running.

[Scot Minesinger]

I have the exact same problem on a 72, let me know if you figure it out.  I have spent a lot of time trying too and have given up.  Installed a voltmeter and just ignore it.  However, would like to resolve.  Just purchased a "short finder" and maybe that will help.

[35-709]

My Gen light came on and stayed on eventhough it was charging, but it was charging too much.  A new internal regulator fixed it.

[Scot Minesinger]

Geoff,

Internal to the alternator?  I tried a few alternators to no avail.

[35-709]

Yes.  Internal to the alternator.  Oh, '71, are we talking an older type external regulator here?

[willowbilly3]

First test condition of your battery while not running. Should be 12.6-12.8v Check grounds, belt tension. Should have 14+ volts while running.

It's a new battery. I know how to test. 13 + volts might be a little weak on the charging but it shouldn't have a bright constant gen light.
I used to be an ASE certified tech, worked on thousands of cars, just have a little brain fart here and don't want to buy a new regulator just for testing purposes. I have considered going to a newer internal regulated Delco but changing from one junk crappy design to another seems like a move sideways. Never was a fan of Delco alternators, especially not the I/R, changed 50 of them to one for any other type. Maybe I'll put a 3G Ford on it,lol.

[Scot Minesinger]

I feel your pain on the 72 Eldorado with gen light on, when charging system works.  This car had a butcher install a modern radio after I got it.  The gen light was off and then it went on for no reason, so I cannot blame the radio.  Got to be a short somewhere allowing bulb to light.  It will not light when ignition key is turned to run position with car off as a test, and neither do any of the other warning lights work in test position.  It could be poor connection to printed circuit board.

[willowbilly3]

 I guess I need to find a wiring diagram and track it down, seems like I remember those idiot lights function on some sort of differential. I've just been putting volt meters in for so many years I kinda forgot but I just want this car stock and correct. I'll let you all know when I figure it out, probably something simple like a poor ground.

[mgbeda]

I don't know if your '76 has the same alternator set-up as a '76.  The '76 (and similar) ones sometimes had a faulty diode in the alternator that caused only one problem- the generator light staying on, dimly.  The rest of the system could still work fine.

-mB

[willowbilly3]

 Found it. Replaced the fuse that's labeled TRANS after looking at this diagram.

http://oldcarmanualproject.com/manuals/Cadillac/wiring/71-80/71-72%20Cadillac%20Deville.gif

[Scot Minesinger]

willowbilly,

Thanks for this post.  My "trans" fuse is also blown and there is a short because as soon as you replace it, the fuse blows again.  Coupled with Steven Tuck's body fuse blowing and the discussion on short circuit finder tools, I should be able to sort this out.  I really was at a loss and the car seemed fine otherwise, so you may have really helped me with my 1972 Eldorado-will keep you posted.