Alternator/regulator trouble
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Posting Guru
Joined: Feb 2007
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From: Wingo, Ky
Alternator/regulator trouble
The alternator and regulator on my 73 F100 were replaced abou 3 months ago and everything as been fine.
Well today I went outside and turned the key to accesory to run the radio while I cleaned on the engine. After a while I started smellin somethin like the new burnin off of something. For some reason I thought to touch the alternator and regulator, both of them were warm, everything else under the hood including wires and in the cab was ice cold b/c truck has been setting without being started for about a week.
Is this normal? I disconnected the battery for percaution. I noticed my alternator light was on with key in accesory position. I thought it only came on with key in run without engine running? Thanks.
Well today I went outside and turned the key to accesory to run the radio while I cleaned on the engine. After a while I started smellin somethin like the new burnin off of something. For some reason I thought to touch the alternator and regulator, both of them were warm, everything else under the hood including wires and in the cab was ice cold b/c truck has been setting without being started for about a week.
Is this normal? I disconnected the battery for percaution. I noticed my alternator light was on with key in accesory position. I thought it only came on with key in run without engine running? Thanks.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
Yikes; that's an odd one. You're correct, the regulator shouldn't be getting any power with the key in ACC. Is there any chance you shorted or bumped something while cleaning the engine? It would make more sense that the problem is a result of something getting knocked under the hood, than the accessory circuit being powered on.
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From: Wingo, Ky
I looked everything over and I don't see nothing wrong. Truck was just fine when I parked it last week. So I have no idea. I cranked it up to see what would happen and the alt light flashes off and on with engine at idle and goes out if I idle it up some.
This truck just doesn't ever give me a break.
This truck just doesn't ever give me a break.
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From: Wingo, Ky
I just went outside and poked around with a test light some. The red/green and yellow wire at the regulator connector have power with key in acc. Would the little capaciter (I guess thats what its called) under the regulator have anything to do with it?
Truck starts fine, runs good, everything else on the truck is working correctly. I don't understand whats happening. I checked all the wires under the hood they all seem fine.
I really hope it is something to do with the cheap made regulator and alternator I got from Advance Auto Parts.
Truck starts fine, runs good, everything else on the truck is working correctly. I don't understand whats happening. I checked all the wires under the hood they all seem fine.
I really hope it is something to do with the cheap made regulator and alternator I got from Advance Auto Parts.
Fleet Mechanic
Joined: Jan 2010
Posts: 1,287
Likes: 17
From: San Carlos, CA
This sounds like your alternator is acting as a load when your accessory switch is on. Current should only pass one direction from your alternator and not back in. I would check your accessory switch wiring just to be sure but most likely you will need to replace your alternator and regulator again.
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From: Wingo, Ky
Well, I got the volt meter out. 12v with truck off. 12v with truck running. Aint that a pain in the @ss?
Whatever weird thing the alternator did you think it toasted the regulator too? Both replaced at the same time along with battery.
Whatever weird thing the alternator did you think it toasted the regulator too? Both replaced at the same time along with battery.
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Posting Guru
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From: Wingo, Ky
Well while I am waitin for more feedback I came inside drank some cold water then went back to fiddle a little more. I disconnected the alternator, I took it comepletely off the truck and laid it on the ground. Alt light still comes on with key in acc.
Only way to make the light go out in acc is to unplug the regulator. I don't get it, I've checked connections and sanded down grounds. Everything seems to be fine, none of the wires even have cracked coatings, just faded colors.
Radio works correctly when key is in acc.
What else do I need to do to help narrow it down for you guys, since I can't seem to find the problem myself.
Also what would a normal batt voltage read when the engine is running? Mine seems to be around 12 to 12 and a half, so barely charging I guess. Thanks for any help.
Only way to make the light go out in acc is to unplug the regulator. I don't get it, I've checked connections and sanded down grounds. Everything seems to be fine, none of the wires even have cracked coatings, just faded colors.
Radio works correctly when key is in acc.
What else do I need to do to help narrow it down for you guys, since I can't seem to find the problem myself.
Also what would a normal batt voltage read when the engine is running? Mine seems to be around 12 to 12 and a half, so barely charging I guess. Thanks for any help.
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Fleet Mechanic
Joined: Jan 2010
Posts: 1,287
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From: San Carlos, CA
My truck sits at 13.5 + VDC at idol. If you alternator is getting hot when its not doing anything then you have current getting past the regulator and back into the Alternator. Since an alternator has windings it is basically a large load resistor to drain your battery. An altornator has a rectifier that will convert AC to DC but it will also prevent current from getting back into itself. I would need to see a schematic to tell you anything more about it but if that is faulty then you could have that unusual problem.
A quick test is to unplug the battery lead from the alternator (A+) and put your meter on amps and measure how many amps your alternator is sucking out of your battery. If its anything more than a few hundred milliamps then you might have a problem with the alternator and/or regulator.
-Or-
Just get a new Alternator and Regulator from a reputable auto parts warehouse which is what I would do.
Good Luck!
A quick test is to unplug the battery lead from the alternator (A+) and put your meter on amps and measure how many amps your alternator is sucking out of your battery. If its anything more than a few hundred milliamps then you might have a problem with the alternator and/or regulator.
-Or-
Just get a new Alternator and Regulator from a reputable auto parts warehouse which is what I would do.
Good Luck!
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Posting Guru
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From: Wingo, Ky
I checked that. Truck off with key off and it shows alternator isn't pulling anything from the battery. Batt is showin 12 volts and its been hooked up since this morning. Truck fired right up just a minute ago.
Regulator and alternator gets warm when key is in acc position and alt light stays on.
With key on and engine runnin the truck acts normal. Alt light goes out and alternator charges(except its not charging good). I am going to take it to parts store and have it tested and get another regulator.
Regulator and alternator don't get hot or anything when truck is running. So I guess for now until I find the problem I just won't use the acc side or run the radio while im out fiddlin on it.
With alternator unhooked the alt light still comes on in acc position. So I next unpluged the regulator, light went out. So I then checked for voltage at regulator connector, there was power at the red/green and yellow wires. From what I understand these wires ahould be "dead" when in acc position.
Just for the heck of it I checked for power to the coil, there was none. Glad one thing checked out normal.
Regulator and alternator gets warm when key is in acc position and alt light stays on.
With key on and engine runnin the truck acts normal. Alt light goes out and alternator charges(except its not charging good). I am going to take it to parts store and have it tested and get another regulator.
Regulator and alternator don't get hot or anything when truck is running. So I guess for now until I find the problem I just won't use the acc side or run the radio while im out fiddlin on it.
With alternator unhooked the alt light still comes on in acc position. So I next unpluged the regulator, light went out. So I then checked for voltage at regulator connector, there was power at the red/green and yellow wires. From what I understand these wires ahould be "dead" when in acc position.
Just for the heck of it I checked for power to the coil, there was none. Glad one thing checked out normal.
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Posting Guru
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From: Wingo, Ky
I am goin to take the alternator and regulator back tomorow to be exchanged. I cranked the truck up today to move it and the alternator bearings started squealing like crazy. I removed belt and sure enough alternator makes a whinin/grindin noise when turned by hand.
The original alternator lasted for 37yrs(with the exception of brushes being replaced once), reman one lasted 3 months.
The original alternator lasted for 37yrs(with the exception of brushes being replaced once), reman one lasted 3 months.
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Posting Guru
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From: Wingo, Ky
Just a thought. When I replace the alternator and regulator again if I still have the alt light on in acc position could my ignition switch be faulty? I see no problems with any wiring.
MSEE
Joined: Apr 2004
Posts: 10,386
Likes: 35
From: Austin, TX
The ALT light receives 12 volts on one side from the hot-in-RUN output of the ignition switch. It has a path to ground through the regulator, which is why it first comes on when you turn the key. A field relay ties the other side of the ALT light to 12 volts when the alternator starts producing current, shutting the light off.
The only way the ALT light can come on is by power applied through the ignition switch. It shuts off when you disconnect the regulator because you're disconnecting the light's path to ground.
The most likely cause is that your ignition switch is shorted, as you suspect. It looks like your switch is powering the hot-in-RUN circuit when you are in accessory. You could verify this by trying to turn the heater on with the key in accessory. If it turns on, then the ignition switch is the problem. This is because the blower motor is part of the hot-in-RUN circuit, just like the regulator. The ALT light should not come in in accessory.
The only way the ALT light can come on is by power applied through the ignition switch. It shuts off when you disconnect the regulator because you're disconnecting the light's path to ground.
The most likely cause is that your ignition switch is shorted, as you suspect. It looks like your switch is powering the hot-in-RUN circuit when you are in accessory. You could verify this by trying to turn the heater on with the key in accessory. If it turns on, then the ignition switch is the problem. This is because the blower motor is part of the hot-in-RUN circuit, just like the regulator. The ALT light should not come in in accessory.
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From: Wingo, Ky
Well I replaced the regulator and alternator again and now im getting a good 14 volts.
Problem is the alt light still comes on with key in acc. I tried the heater with key in acc and it came on. I tried a switch from my everyday driver and a new switch and it still does it so I guess there is a problem somewhere. The wiring and plug in going to the switch looks great, no cracking of coating or anything.
Until I get this problem figured out I still want to be able to run my radio when I am tinkering on it. Can I run a constant hot wire to it? Where would the best place be? Only problem I see with this is it will run my battery down if I forget to turn the radio off.
Just thought of this, ok you know my alt light is coming on when key is acc. But the oil light is not. The oil light only comes on when its supposed to, with key in run and engine off.
Problem is the alt light still comes on with key in acc. I tried the heater with key in acc and it came on. I tried a switch from my everyday driver and a new switch and it still does it so I guess there is a problem somewhere. The wiring and plug in going to the switch looks great, no cracking of coating or anything.
Until I get this problem figured out I still want to be able to run my radio when I am tinkering on it. Can I run a constant hot wire to it? Where would the best place be? Only problem I see with this is it will run my battery down if I forget to turn the radio off.
Just thought of this, ok you know my alt light is coming on when key is acc. But the oil light is not. The oil light only comes on when its supposed to, with key in run and engine off.