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71 Eldorado Gen Light

Started by suchan, June 14, 2014, 09:07:17 PM

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suchan

My '71 Eldorado convertible wasn't running right, rough idle, very rough cold idle, so I took it to my mechanic (this is my first '70's Caddy; previous hobby cars were all '30's-'50's, and all these wires and hoses mystify me). He adjusted the carburetor and idle, fixed a vacuum leak, it's running great, but the GEN light stays on. He tried replacing the alternator, checked the output (14/plus), and can't figure out what's with the GEN light. He's doing this gratis as the problem didn't arise until he worked on it, but I live 30 minutes out of town, I don't want to leave it overnight in his parking lot, and having the wife chase me to the repair shop is getting old.
Any ideas?
Southworth, Washington
CLC #28060
1937 LaSalle 5019 Sedan
Cars that got away:
1930 Ford Model A Roadster and AA Flatbed
(2) 1938 Buick Sedans
1942 Chev Blackout Coupe
1953 Ford F100
1955 Ford Victoria
1956 Sedan DeVille
1962 Peugeot 403
1965 Peugeot 404
1971 Eldorado Convertible

TJ Hopland

Is the 71 and internal or external regulator?
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

suchan

The mechanic first thought a diode had failed, but then ruled that out, so I'm assuming it's internal.
Southworth, Washington
CLC #28060
1937 LaSalle 5019 Sedan
Cars that got away:
1930 Ford Model A Roadster and AA Flatbed
(2) 1938 Buick Sedans
1942 Chev Blackout Coupe
1953 Ford F100
1955 Ford Victoria
1956 Sedan DeVille
1962 Peugeot 403
1965 Peugeot 404
1971 Eldorado Convertible

"Cadillac Kid" Greg Surfas 15364

Check ALL the electrical connections at the alternator, especially the small one that plugs into the alternators top. Be sure that both of the wires are actuay connucted to the spahe in the plastic connector itself.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

TJ Hopland

Looking at parts store lists it appears that it is an internal regulator. 

I don't have a 71 manual but typical GM for the era is the alternator has 3 wires.    If you don't have these 3 connections let us know.  You should but perhaps things have been modified.   You could have a GM alternator with only the one stud connection or a newer unit with 4 pin plug.   Also does this still have an original 'points' style distributor?   Or does it have something like a Pertronix in it?  Or an HEI from a newer car?

So assuming stock:
   
Fat wire from big stud on back goes to battery.

2 pin connector the farthest pin from the big stud terminal has a orange wire that goes to the big stud terminal.  This is the 'sense' terminal that the internal regular uses to evaluate what the system voltage is.  In some designs this wire will go all the way to the fuse box.  Where ever that terminal is connected is the point in the system where the voltage will be regulated to the set point.  In this case if the set point is say 14.3 volts you should be getting 14.3 volts at that stud.   At the battery which is through another 2 feet of cable you may only be getting say 14.0.

2 pin connector the close pin from the big stud terminal has a brown wire that makes its way to the gen light on the dash.   Other side of the GEN light gets fed (along with the most of the rest of the lights and gauges) from the gauge fuse (sometimes labeled INST) which is only live with the key on.

So what you got is one side of the light gets a +12v signal from the fuse/key.   At rest the small close to big terminal terminal on the alternator basically appears as a ground so the result is gen light lights.    When the alternator begins turning the regulator 'sees' the +12v signal coming through the gen light and 'turns on' the regulator.   With the alternator spinning and the regulator turned on because it 'sees' that +12v coming through the bulb it should be generating power.  In this state that terminal outputs system voltage.   This means that the alternator side of the gen light is getting say 14.3 volts.   The other side comes from the key on fuse and is also going to be fairly close to full system voltage say 13.9.  0.4 volts is not enough to light the light so everyone should be happy.

If the alternator is not putting out full power that terminal will be what ever the alternator is putting out.  IF its only putting out say 9 volts one side of the lamp is 9 v and the other is 12v, thats a difference of 3v which would dimly light the bulb. 

The reason I asked about the distributor is that most of the electronic conversions require slight mods to the power feed.  Sometimes you can end up with the distributor and the alternator back feeding each other so the engine won't shut off with the key.  There are easy ways to fix that problem but some people go with a much more complex 'fix' that causes other issues. 


StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

bcroe

Quote from: TJ HoplandIs the 71 and internal or external regulator? 

My 72 Chev book shows a mechanical regulator.  I thought the internally regulated
came out with the HEI.  Bruce Roe

TJ Hopland

For some reason I am thinking 70 or 71 was the change year for Cadillac, at least with the common size alternator,  perhaps for a few years it depended on the size.   
StPaul/Mpls, MN USA

73 Eldo convert w/FiTech EFI
80 Eldo Diesel
90 CDV
And other assorted stuff I keep buying for some reason

suchan

Thanks for the advice. When I get it fixed, I'll post the solution.
Southworth, Washington
CLC #28060
1937 LaSalle 5019 Sedan
Cars that got away:
1930 Ford Model A Roadster and AA Flatbed
(2) 1938 Buick Sedans
1942 Chev Blackout Coupe
1953 Ford F100
1955 Ford Victoria
1956 Sedan DeVille
1962 Peugeot 403
1965 Peugeot 404
1971 Eldorado Convertible

mgbeda

On my '76, which may or may not be the same alternator, the generator light came on dimly back in the 80's.  But tests showed that the alternator was putting out plenty of juice.  The mechanic I used to work for said there was a diode, internal to the alternator, that would burn out, causing no problem except the light coming on.  I drove it daily for years like that before the factory alternator finally wore out.  You are probably more likely to fix it properly.

-mB
-Mike Beda
CLC #24610
1976 Sedan DeVille (Bessie)

suchan

That's one of the first things my mechanic thought of, but replacing the alternator didn't fix the problem. Maybe a bad replacement?
Quote from: mgbeda on June 16, 2014, 02:50:41 PM
On my '76, which may or may not be the same alternator, the generator light came on dimly back in the 80's.  But tests showed that the alternator was putting out plenty of juice.  The mechanic I used to work for said there was a diode, internal to the alternator, that would burn out, causing no problem except the light coming on.  I drove it daily for years like that before the factory alternator finally wore out.  You are probably more likely to fix it properly.

-mB
Southworth, Washington
CLC #28060
1937 LaSalle 5019 Sedan
Cars that got away:
1930 Ford Model A Roadster and AA Flatbed
(2) 1938 Buick Sedans
1942 Chev Blackout Coupe
1953 Ford F100
1955 Ford Victoria
1956 Sedan DeVille
1962 Peugeot 403
1965 Peugeot 404
1971 Eldorado Convertible

J. Skelly

Based on my experience when I owned my '71 Eldo, remanufactured alternators were junk, and this was in the 70s and 80s.  I had the same issue with the generator light and when I read this thread, a bad diode was the first thing I thought of.  Another issue is the threads are often stripped on the bottom of the housing where the long bolt goes in from the radiator side.  I found this out the hard way after finally getting the sleeve and bolt lined up properly and it wouldn't tighten up.     
Jim Skelly, CLC #15958
1968 Eldorado
1977 Eldorado Biarritz
1971 Eldorado (RIP)

Mike Shawgo

Hi, don't know if you got this fixed, but this happened to me once, and it drove me crazy.  I replaced the generator, nothing worked until I happened to look at the fuse box diagram, and noticed there was a fuse for the generator light.  Put in a new fuse, and that fixed it!  I don't have the fuse diagram any more, but there should be something on the diagram that will give you the clue which one it is.

Mike Shawgo

Mike Shawgo

Found my fuse chart--Fuse #5, 10 AMP, controls brake warning light, TCS vacuum solenoid, downshift solenoid, fuel gage, generator light, low oil pressure indicator, water temperature warning light.

--Mike Shawgo