Wiring a 2 alternator system
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On this engine the alternator is fixed and the only adjustment seems to be in the idler pulley. The 3G off a car will fit, using a different existing hole in the alternator bracket. Looks like it will move it out a couple of inches. Doubt the idler will adjust that much. Was hoping someone has done this upgrade on the 300 & could tell me what belt to use, or how they determined which size belt to use.
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Hi I am considering a 3G alternator upgrade for my 86 F150. My main concern is that I don't have the calmness to wire myself and am too cheap to hire the work out, so I was wondering with the 3G install do I need to replace the two 10gauge wires comming off the old alternator or can I reuse them and just add one or two more 10gauge wires to my auxillery fuse box using a 30 or 35 amp fuse on each additional main wire. I also was looking at cje07's list of parts required for the swap and was wondering if I would have to get the pulley spacer, I don't want to buy anything more than I need to because I am not very mechanically inclined and I don't like spending money to hire work out. Thank-you for all of the help you can give me. Thanks 
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Hello afarmer
I did the upgrade, to my 1990 300 inline 6, and it was very easy. The alternator fit the bracket, and the original belt fit fine.
Instead of adding wires. try doing what I did. I got the harness when I got the alternator at a upull parts yard. Got some cable end ring terminals and a fuse holder with fuse from an auto stereo shop. Crimped and soldered the four cable ends
Pulled out all the old wiring, and only cut the red/green wire. This is the only wire I spliced into the new harness. Everything else plugged in, or ended with a cable end.The upgrade works fine and looks good too.
I did the upgrade, to my 1990 300 inline 6, and it was very easy. The alternator fit the bracket, and the original belt fit fine.
Instead of adding wires. try doing what I did. I got the harness when I got the alternator at a upull parts yard. Got some cable end ring terminals and a fuse holder with fuse from an auto stereo shop. Crimped and soldered the four cable ends
Pulled out all the old wiring, and only cut the red/green wire. This is the only wire I spliced into the new harness. Everything else plugged in, or ended with a cable end.The upgrade works fine and looks good too.
Elder User
Joined: Feb 2002
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From: Rochester
Originally Posted by afarmer
Hi I am considering a 3G alternator upgrade for my 86 F150. My main concern is that I don't have the calmness to wire myself and am too cheap to hire the work out, so I was wondering with the 3G install do I need to replace the two 10gauge wires comming off the old alternator or can I reuse them and just add one or two more 10gauge wires to my auxillery fuse box using a 30 or 35 amp fuse on each additional main wire. I also was looking at cje07's list of parts required for the swap and was wondering if I would have to get the pulley spacer, I don't want to buy anything more than I need to because I am not very mechanically inclined and I don't like spending money to hire work out. Thank-you for all of the help you can give me. Thanks
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Joined: Apr 2006
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I am tring to get the alternator off of ebay for under $30.00 including shipping. The alternator will eaither have the serp pulley or won't have a pulley. My truck has the dual V belt pully on the alternator. I know that it is recomended to replace the wires but I don't want to spend the money right now because in october I am getting an 1983 F250 that I'm gonna put my engine into. I just want to have this setup as a temporarry job because my 86 is so baddly rusted out that I am just keeping it so that I can pull the engine transmission and possible the rear axle gear set. The wiring will be replaced later with 2gauge from the battery to the solenoid and from alt to solenoid and solenoid to starter but I don't want to run the new wire in the temp truck as it is just for me to expareament with untill I get my F250 body and frame. Thank you for your responses. I will see if I can find an alternator with harness if at all posible, but I was thinking in case I don't get an alternator I'd just run temporarry wiring to support the alternator. Thank you again.
Last edited by afarmer; May 19, 2006 at 02:51 PM. Reason: mis typed
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I have another question about the upgrade will my stock ammeter work??? According to the diagram in the 1980-1996 Haynes manual My trucks alternator connects to the gauge with the GRN/Red wire, the wht/blk is stator and the yel/wht and blk/orn are battery. But for the newer vehicles 93-96 it shows the GRN/RED wire going to a bulb and resitor heading to the ignition switch, now I am assuming that the ammeter gauge would be in the same wiring loop as the idiot lamp but I am not sure. My current idea for my swap is to use the bearing like cje07 has and then to just add 2 more 10gauge wires until I replace the body and frame of my truck. Thank-you all for any help you can give me.
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Joined: Jan 2001
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From: Virginia
Your stock ammeter will work so long as you keep the original wiring harness in the truck now. The stock ammeter does not hook to the grn/red wire. It hooks to a piece in the large main alt output wire called a shunt. If you change this wire out, or add more that go around this shunt, then the ammeter will not work or not be accurate.
Best solution? Forget the stock ammeter and add a aftermarket voltmeter to the system when you add the new alternator.
Best solution? Forget the stock ammeter and add a aftermarket voltmeter to the system when you add the new alternator.
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I am confused as autozone and Haynes has my 86's alternator wiring different than any other year. I am wondering if this is correct. I think that it could be as the 1986 F150 was the first offical model year with the 2G alternator but it had the ammeter gauge yet. I know that some 1987 model year trucks had the 2G alternator with a volt meter. The diesel and Air conditioned models of 87 trucks had the old externally regulated. I was told that some 86 models also had the 1G style alternator. I checked mine is the 2G style 65amp. I took these following diagrams from autozone please tell me if they appear to be correct
Last edited by afarmer; May 19, 2006 at 10:39 PM. Reason: diagram is way too big
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Sorry if I seem a little rude, I have been sick over the past few days. If I offened anyone with my responses I didn't mean too. Okay now I couldn't get the diagram to shrink correctly on my pc so I hope that it turned out for ya'll. I am sterching myself a little too thin tring to save ca$h on my truck but yet have it roadworthy so I can go 1200Miles before having to junk it. I have had to replace so many part and found out that my radiator leaks. 
I am hoping that I can find a cheap one for under $30.00. I will admit I know that the ammeter sucks but I always liked watching it go back and forth while my turn signals are on. I also have a ciberdine voltmeter mounted in the dash to the right of the ammeter so having the ammeter accurite isn't a mian concern. I sold the tach too buy the voltmeter about a week ago. I had the aftermarket tach 400rpm mounted where the stock tach was suppose to go, I got a different block off plate for the tach location but am thinking I should have installed my voltmeter where I had the tach it would have been easier to install. . Thank you again for all the help you've all been weather in this post or others. Thanks
Sincerly, Alexander
I am hoping that I can find a cheap one for under $30.00. I will admit I know that the ammeter sucks but I always liked watching it go back and forth while my turn signals are on. I also have a ciberdine voltmeter mounted in the dash to the right of the ammeter so having the ammeter accurite isn't a mian concern. I sold the tach too buy the voltmeter about a week ago. I had the aftermarket tach 400rpm mounted where the stock tach was suppose to go, I got a different block off plate for the tach location but am thinking I should have installed my voltmeter where I had the tach it would have been easier to install. . Thank you again for all the help you've all been weather in this post or others. ThanksSincerly, Alexander
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From: Virginia
The above diagram looks correct for a internally regulated alternator with a dash "gen" light(idiot light). That's what the grn/red goes to.
If yours has the factory ammeter, the wiring is basically the same except the grn/red will go directly to the ignition switch. The ammeter will be hooked into the large black/orange wires. Probably what you will find is where the blk/orange wires are tied together, you will have to start unwrapping the harness. Somewhere between were the blk/orange wires are spliced together, and the battery + connection, you will find a strange looking piece in the wiring with two little wires spliced in on either side. These two little wires go to the ammeter. If you keep this special little piece with the two wires, and splice it into the new alt output wire, then you ammeter will still work.
If yours has the factory ammeter, the wiring is basically the same except the grn/red will go directly to the ignition switch. The ammeter will be hooked into the large black/orange wires. Probably what you will find is where the blk/orange wires are tied together, you will have to start unwrapping the harness. Somewhere between were the blk/orange wires are spliced together, and the battery + connection, you will find a strange looking piece in the wiring with two little wires spliced in on either side. These two little wires go to the ammeter. If you keep this special little piece with the two wires, and splice it into the new alt output wire, then you ammeter will still work.
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Thank you, I think that I may have been mistaken on the diagram. I guess that I should look mre carefully next time thanks for getting me correct. I am still unsure if I will do the swap. I might wait untill later this year. Thank you for all of your information.
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