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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #1 ·
The generator light just came on in the DeVille tonight. I checked the voltage, and it's between 13 and 14 at idle, seems not bad. The FSM doesn't seem to have a very clear troubleshooting flow chart for this, and one of the main troubleshooting methods they talk about requires a special tool that's not available. I'd like to figure out what's wrong, if it's something that has failed, or maybe something like a VR out of adjustment, and then address the issue. If replacement parts are needed, I would definitely want to use an original style alternator and external voltage regulator. Anyone with experience on this system have any suggestions where to begin?
 

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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #2 ·
Put another way, does anyone know how to adjust the voltage regulator without the VAT-20 tool called for in the FSM?
 

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Super Moderator
2014 ELR
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10,425 Posts
The 70 still has an external reg? My 65 has the external, my 71 has internal. Not sure on the year changeover.

Anyways, the only problem I ever had with a voltage regulator was on my 65. Jump started the car one spring, and the gen light stayed on. Changed the voltage regulator, and everything was fine. Parts store had it in stock for 14 bucks. Probably worth picking up a voltage regulator to see if that fixes the problem.
 

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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #4 ·
You could be right. My concern is that, since it's adjustable, I would want to adjust even a new voltage regulator, same as I double-check the gap on new plugs. Without access to the VAT-20, is there a backyard way to do this? The simplest way I would guess would be to hook up a meter and make sure that the voltage stays within range, say 12.5-14.5 depending on load. I may try the replacement though. It's annoying because it's been perfectly fine, and then suddenly for no reason the light comes on.

I was also trying to figure out when the switch to internal happened. Sounds like it was maybe in '71. What is your '71, DeVille, Fleetwood? I was wondering if maybe there was a correlation between this and the switch to HEI.
 

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2014 ELR
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No, my 71 is a Pontiac.

I never knew that regulators were adjustable. I just installed the new one and it worked fine.
 

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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #6 ·
Gotcha. Well, I have some updated info, in case this rings a bell to anyone. The gen light previously wouldn't come on in accessory position, or when the ignition was on and the engine was off. When the engine was running, the gen light would come on bright, but when adding certain loads, the light would go from bright to dim. (closer to zero, the light is illuminated when there is an imbalance up or down on either end of the bulb circuit) Discovered that the battery lead on the alternator was not doing so good, the terminal on the 10ga wire was nearly broken, and there was some evidence of heat damage, so I replaced it. Problem still exists. Cleaned up the terminals on the voltage regulator, they were a bit dirty looking. Problem slightly improved, the gen light is now on extremely dim while engine is running, and is illuminated in the accessory and ignition positions when the engine is off. Problem is now, the voltage appears lower, 12.5 with no load, and under 11 with headlights and blower motor on high. I can't test the alternator because I don't have the VAT-20 tester, but it looks like it's the alternator that might be bad. Blown due to the high resistance in the battery lead? I'm going to put a charge on the battery and check again, I'm assuming the voltage will be higher when the charge is fresh, and start dipping down as it's depleted. If this is the case, I'll replace the alternator and see what happens.
 

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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #8 ·
I'll give it a try. I wasn't sure if they'd be able to do this considering it's externally regulated. I think Chryslers were externally regulated much later, maybe into the '80s, so I guess it's not that unusual.
 

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70 Deville 77 Fleet 78 Seville 92 Deville 03 Deville
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3,310 Posts
FYI JC Whitney used to sell some kind of solid state external regulators for older GM cars. I always figured i would try one sometime but haven't had to yet.
 

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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #10 ·
Check THIS out...they can't test the externally regulated alternators in the store, so I just picked up a rebuilt one and a new solid-state replacement voltage regulator. Put it all back together, checked all the underhood wiring, fixed one bad connector, everything else looks good to go. Start it up....13+ volts at the battery while running now instead of 12, but STILL have a gen light. What the hell could this be? Battery is new and good. Alt is new and good. VR is new and good. Connections are good. ?!? I'm guessing high resistance on the OTHER side of the bulb circuit, i.e. lower than alternator output on the other side due to a bad connection somewhere, therefore not balancing voltage across lamp and allowing it to come on. I'm going to go look at the FSM some more and then bang my head against the wall. ANYONE else with a persistent gen light?
 

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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #12 ·
FIXED!! The gauge/trans fuse was blown. This is on one side of the gen lamp, and apparently if this is blown, the light will stay on permanently.

I still have some other questions or things I'm curious about, but I guess I'll find out more as I drive it. One concern is, as I had mentioned, I noticed evidence on the wire from the alternator to the battery of heat damage, and I think this was caused by a failing connector causing high resistance and in turn causing the alternator to overcharge. I HOPE that this was also the cause of the blown fuse, because if not, then there is something else going on that's going to keep blowing fuses. I noticed something else strange that I'm going to have to look at, on the vacuum advance vacuum solenoid. This is also on the same circuit with the gen lamp and the kickdown solenoid. I think there's supposed to be a resistor between the two terminals on the vacuum solenoid, and it looks like someone might have installed a jumper instead. I'll take a look now, but if there still are problems, this will be the first place I look.

Thanks for your help and input on solving this issue.
 

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84 Coupe w/500
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5,671 Posts
Glad you got it fixed. Thanks for the diagram, I've always wanted more info about this circuit and that diagram clears it all up for me. "If it were me" I would look at the vacuum solenoid to see if there was supposed to be a resister soon. Too much current could slowly melt wires, could take a month, could take a year but if too much current is getting through...something has to give.
 

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1970 Coupe DeVille, 2002 Eldorado Collector Series
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200 Posts
Discussion Starter · #14 ·
I will definitely look before I start the car again. The thing is, it has a very official look about the way it's installed, it's hard to describe. For a second, I thought it might have been a decades-old "free mod" intended to circumvent one of the first emissions controls. I'll post what I find.
 

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1968 Convertible
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268 Posts
Ok, well this is old post but I am dealing with the same problem.

Lights started to Pulse. So I thought I'd replace the VR

My old VR had has an underside that looks like the Airtex 5K3 in Rock Auto, the new one is an AC Delco D663.

Now the Gen light comes on, sound of a sad little buzzer somewhere, and it does not go away until I give it a little throttle.

Help?
 

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1970 Coupe De Ville//Cessna 172
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551 Posts
The old regulators are adjustable. They have 3 sets of points in them. I'm not sure when they switched over to solid state but you could adjust the old ones. They were temp sensative so depending on the temp you would over/under charge your battery.
 
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