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kychevyguy View Drop Down
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    Posted: 29-August-2022 at 12:44PM
I have a 76 Ranchero GT with the 351M/400 auto. Lately, the alternator light has been slowly coming on. When I start the car, everything is fine but after about 1 minute of idle, the light will very slowly start glowing. After about 3 minutes, the ALT light is at full glow. It has a new battery, alternator, voltage regulator, starter solenoid. The battery shows about 13.75v at idle, so it is being charged.

Has anyone else ever experienced this "slow glow?"
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
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Does engine RPM make a difference? 

13.75V is low. It should be in the mid 14s.
1972 Gran Torino station wagon, light blue, 351C 2V, prior owner upgraded to 4V (2V heads), originally had a C4 but prior owner changed to C6 for some reason.
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kychevyguy View Drop Down
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Originally posted by Inkara1 Inkara1 wrote:

Does engine RPM make a difference? 

13.75V is low. It should be in the mid 14s.

RPMs do not make any difference to the light, I have not checked the volts at higher RPMs.
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
2015 Volvo XC60 R-Design "Sven"
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Rockatansky View Drop Down
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how did the contacts in the regulator harness plug look when you changed the regulator?
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kychevyguy View Drop Down
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Originally posted by Rockatansky Rockatansky wrote:

how did the contacts in the regulator harness plug look when you changed the regulator?

The contacts looked good and normal. I did use a touch of dielectric grease on the contacts.
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
2015 Volvo XC60 R-Design "Sven"
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The insulator grease may be acting like a resistor.  Not a recommended idea.
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Rockatansky View Drop Down
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Originally posted by Greg73Oregon Greg73Oregon wrote:

The insulator grease may be acting like a resistor.  Not a recommended idea.
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Greg73Oregon View Drop Down
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Without going into a lengthy discussion, you have low voltage problem.  As the other responder advised, your voltage should be 14.6V to 14.8V. (This accounts for making up for/overcoming the internal resistance of the battery.  If the battery was "perfect", it would have no internal resistance and could providing infinite current).
Unless you are clear about your relay contact material: silver, fine silver, silver alloy, silver cadmium oxide, silver tin indium oxide, silver copper nickel, nickel, etc., I'm suggesting that dry contacts are used.
In fact, some relay contacts made for higher currents are designed such that the arcing that occurs when opening & closing actually clean the contact area.
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72 RS 351 View Drop Down
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I have always wondered about what the proper amount of dielectric grease is, too much versus nothing etc.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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kychevyguy View Drop Down
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Just for clarification: neither the new voltage regulator nor the dielectric grease made any difference at all in the prognosis of how the car is acting. After everything that I have done and replaced, it is responding 100% the exact same as before I started touching anything. That is why I am baffled about this.
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
2015 Volvo XC60 R-Design "Sven"
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Rockatansky View Drop Down
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have you had the charging system tested in the car?

if that's not an option pull the alt off and take it in for testing

lately new parts are Censored
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handsofstone View Drop Down
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Load tester at Harbor Freight is like $20. Worth the try.
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Rockatansky View Drop Down
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VAT-40 test free at the parts store
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kychevyguy View Drop Down
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It seams to be a series of electrical shorts...
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
2015 Volvo XC60 R-Design "Sven"
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kychevyguy View Drop Down
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Okay, y'all gonna need your thinking caps on. Supposedly, there is a 15 ohms resistor located someplace on the green/red stipe wire for the charge indicator light. This resistor is what is suspect. I talked to an experienced ford technician and he stated that is why the ALT light will slowly come on. He states that once it hits 3 volts on either side of the resistor, it will slowly build up an indication, hence the light.

So, the ultimate question is now, does anyone know where this resistor is located? Could it be inside the small voltage regulator that is on the back of the instrument panel?
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
2015 Volvo XC60 R-Design "Sven"
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I found it on the wiring schematic, but where it is physically located, I don't know.
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It looks like it might ve close to connector 482. The entire wiring diagram can be downloaded here:


I don't have time to go through it now, but I believe they usually show you what each of the connectors look like and each connector's location.


Edited by 72FordGTS - 12-September-2022 at 2:18AM
Vince

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kychevyguy View Drop Down
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UPDATE: After many, many, many trials and errors, I have found the culprit, and it was a surprise. The rebuilding of the ignition switch is the smoking gun that finally fixed it! I went through the entire electrical system of the whole car (yep, I completely went through EVERYTHING) and the ignition switch did not look kosher. I took it out and went through it, soldering loose items, cleaning and put it back in. Alternator light since has worked as designed by Ford since then!!!
JT, USAF Ret./Architect
1971 Ford F100 "Lizzy"
1971 Cougar XR7 "Kitty"
1984 Chevy Silverado "Sylvia"
2009 Smart Fortwo Cabrio "Lil Dude"
2015 Volvo XC60 R-Design "Sven"
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Well done, perseverance is your power.
Don
73 Ranchero "Sport 72 front end", floor shift/console, planning EFI 7000 rpm 351 stroker
73 Ranchero GT 351C-4V &4R70W for sale later.
92 Lincoln Mark VII SE GTC, OBDII 347/4R70W
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That’s great news!   Thanks for sharing the root cause!

Chris
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Sorry to bring a post back from the dead, but I’m having very similar-ish symptoms. My alt light will slowly glow when the rpm’s are above an 1,500 rpm’s, at low idle it remains off. It never gets more than maybe 50% bright and kind of flutters on and off while I’m driving. I load tested the battery and it tested strong. I tested the charging system and it passed fine. At idle the battery reads low to mid 14’s, and it increases with more rpms. 
Admittedly, I have not checked my ignition switch yet. But my tachometer (added on) has recently been randomly swinging and when I’m below 1,200 rpm it just falls to zero.
Both of these symptoms are new and but did not start happening at the same time, nor do they appear to be directly tied together. The tach seems to function best at higher rpms, while the ALT light indicates with higher rpms. 
It’s a 71 Torino 500 with a 5.0 roller motor, factory ac, power brakes and power steering. 
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are you aware there's an Instrument Panel Voltage Regulator ?
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Hinmaton View Drop Down
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I suppose I did not. Is this something that can be tested or just replace and see?
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i'd do a little more diagnosis before firing the parts cannon, you say the ALT light comes on stronger at higher rpm? what is the battery voltage when the light is on?  

Originally posted by Hinmaton Hinmaton wrote:

At idle the battery reads low to mid 14’s, and it increases with more rpms. 


low to mid 14's sounds fine but it should not increase with rpm, i have to suspect the charging system voltage regulator is not maintaining a steady voltage, could be the source of the Alt light?
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Hinmaton View Drop Down
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You are correct. The voltage stays a constant 4.2ish no matter the rpm increase. 
Still think voltage regulator?
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