"GEN" warning light on 1970 DeVille Convertible

[jwjohnson86]

Purchased my car midsummer, everything runs great, prior seller had a lot of engine and mechanical work done.  I do not have technical expertise in repair so thought this was a good place to start as a possible diagnosis.

Issue:  "GEN" red warning light illuminated on panel a couple days ago while driving (90 degree day) and has remained on since (several additional drives).  There are no problems whatsoever with starting and cranking the car, the battery is newer, and there is no dimming or flickering of the interior or exterior lights at night (which happened to me on a Pontiac many years ago - the lights dimming was the warning sign of an imminent alternator replacement). 

Thoughts on any possible issues based on your experiences before I consult my local mechanic?  I am ordering a shop manual but do not have one on hand yet.  Hoping to make it to my first CLC event in Hickory Corners, MI at the end of this month - don't want to conk out on the way there!  Thanks.

Happy Motoring,
Jason Johnson CLC #29583

[willowbilly3]

 I just had the same thing on a 71 Coupe Deville I bought and after studying the wiring diagram discovered the fuse marked TRANS was blown.

[joeinbcs]

I had this problem with my '68 Eldorado, and couldn't seem to get to the bottom of it, despite installing a new alternator and voltage regulator.  I took it to Texas Alternator, and they changed a fuse...duh!
Check your fuse before you replace everything!

[Scot Minesinger]

Congratulations on your purchase of a 1970 Cadillac, a great car-yes I have a deVille Convertible too.  You are doing the right thing buying a shop manual.  You will find that you are more skilled than you might imagine at repairs if your just read the manual.  There are many things you can do in a white dinner jacket that will resolve many questions.  To start, you need to also buy if you do not have one already:

1.  A good multi-meter, like Fluke (they range in price from $10 to $100) and they are more toward the top end of the price range but a lifetime product.  This measures volts, resistance (ohms), and usually amps.  For your question with car running go to the battery and measure across the battery terminals volts DC and it should read in the 13.5-13.9 range.  If you have that then the light not indicating correctly could be the issue.

2.  A hand vacuum pump, commonly sold at Auto parts stores as a one man brake bleeder.  This tells you if when many of the engine vacuum driven devices is bad.

We are here to help, please do not hesitate to share your concerns and questions.

Enjoy your Cadillac,

Scot

[willowbilly3]

Also a good 12 volt test light is a must.

[chrisntam]

You'll need tools, time, a factory service manual and money, not necessarily in that order.

If you post a pic of your car, we'll continue to offer advice.  If you don't post a pic, we'll continue to offer advice, but a pic or two would be nice!

[Julien Abrahams]

Basically the same advice that was already given. I think that there is a problem with your regulator or alternator (of which I am not sure if it has an internal or external regulator). If you are able to measure the output of your regulator (for example by using a multi meter to check battery voltage with the engine off, when the engine is idling (at slow idle) and when the engine is revved. Battery voltage should be around 12,5 with the engine off and between 13 and 14,5 volts when it is idling/revved.
I would put my money on a broken diode inside your alternator, but before you start replacing things, first check the voltage.
In addition: as others suggested: check your fuses.

[Lucas Feininger #15674]

I have had the same problem with a 1963 Series 62 convertible and a 1965 Sedan de Ville. In both cases it was the wiring harness (cracked/broken wires) between the voltage regulator and the alternator. These damaged wires can be hard to see -- on the Sedan de Ville all the wires looked good -- the break was where the one of the wires went into the connector.

[jwjohnson86]

All great feedback!  Thanks everyone.  I have a pack of fuses and a volt tester so we'll start there and see where we get.  Added a photo of our new addition...

[Jeff Rosansky CLC #28373]

Good pix. Nice looking car.

[chrisntam]

Right side mirror..........Lucky.............

That's a nice color!

[jwjohnson86]

Thanks all..  Checked the fuse box today and found a blown 10 amp fuse, pulled and replaced that.  Warning light is still on and I also have no headlights.  Everything else electrical on the car works (front and rear turn signals, rear brake lights, etc).  Possible combination of a failed headlight switch and the "gen" indicator around the same time?  Anyone seen these two failures at the same time?  No twilight driving for me for a while.

[Scot Minesinger]

No new advice, all the wisdom is posted, just need to search for the shorts using proper tools and shop manual wiring diagram.  It is very rewarding when you find the problem.

Best of luck

[jwjohnson86]

On the "bright" side the replaced fuse caused my dash ashtray light to illuminate for the first time in who knows how long!  Smoke 'em if you got 'em!

[Bill Young]

Beautiful Car! , You are missing the DeVille chrome marking trim that goes just above the side trim at the rear of the quarter panel on both sides. McVey's has these available on line.

[Rob Troxel]

Does anyone remember the Gen light illuminating when the trunk was open?  Seems like that was the case with my 68 Eldorado and it was mentioned in the owners manual.

[jwjohnson86]

OK, we got hold of a multifunction tester and found zero output voltage coming from the alternator.  Going to replace that, the battery cranking amps were also low so everything's been running off the battery and reducing battery life. 

Thanks for the leads on the missing DeVille rear quarter scripts.  May have been lost in an old repaint long ago. Shopping for a trunk lock cover also, rear marker light lens and a backup light lens.

[Scot Minesinger]

The rear trunk lock cover is a one year only, and they are very difficult to find.  They are not reproduced and few survived.  You may be looking at well into triple digits for a decent one.  The scripts are re-produced and available at reasonable cost.  The rear marker lights are not reproduced, but good used are not difficult to find at reasonable prices.

[Jeff Rosansky CLC #28373]

I had to get a side marker. They are out there.

[jwjohnson86]

Got the alternator out this weekend and took it to Advance Auto Parts to put it on their bench tester. Output no volts so confirmed it died.. Exchanged core for a rebuilt unit, got that installed.  "GEN" light went off shortly after starting and all is well.. Interior courtesy and dash lights significantly brighter also.  Headlight switch works now also.  Thanks for all of the suggestions and advice!
Jason Johnson