Back to generator from alternator - how too?
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Postmaster
Joined: Jul 2008
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Back to generator from alternator - how too?
Actually I pulled an old chevy motor from my recently acquired 52. The 239 flathead I put in the truck still had the generator setup and I would like to stay with that for now. What do I need to do wiring wise to use the generator? I'm trying to reuse as much of the old wiring harness that was in the truck as possible. The current one still has the alternator type plug in place. The system looks to be converted to 12 volt (mostly). Thanks for the assistance.
Freshman User
Joined: Feb 2012
Posts: 43
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It depends if you want 6 volt or 12 volt, if you want 6 volt then google search for a wiring diagram and you'll need a voltage regulator, but you would be better with 12v , depends if money is a problem, they make single wire old look generators in 12v high amp models for that old school look. If you are using the original generator it may be best to find a imilar old truck close by that you can get the wiring out of.
Cargo Master
Joined: Aug 2010
Posts: 2,927
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From: Houston
You need a generator with voltage to match your truck, in your case 12V. You also need a matching regulator. The regulator will be marked ARM, FIELD, and BAT and generator will be marked ARM, FIELD, and GRD. The ARM and FIELD posts are connected together on both regulator and generator. The GRD on the generator is ground and a wire goes from it to one of the mounting screws on the regulator. The BAT on the regulator is your voltage out and goes through your ammeter then out to your starter solenoid (on the battery side).
A stock wiring diagram for your truck can be found here: Google Image Result for http://www.vanpeltsales.com/FH_web/FH_images/FH_electrical-pics/Flathead_Electrical_wiring1948-49truck.jpg
A stock wiring diagram for your truck can be found here: Google Image Result for http://www.vanpeltsales.com/FH_web/FH_images/FH_electrical-pics/Flathead_Electrical_wiring1948-49truck.jpg
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Postmaster
Joined: Jul 2008
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Thanks for the response. Is there a way I can determine whether the generator is 6 or 12 volt? There is a "F" and a "G" stamped on the side of it so I'm guessing this is the Field and Ground. I did not see anything marked ARM although there is a small post with a nut on it on the back of the generator. Hard to see if there was any lettering associated with it.
Also, thanks for the wiring diagram, but is it still a proper reference point if I am 12 v as opposed to the original 6v as is the diagram. Or is it basically the same just running 12v instead of 6? Thanks for the clarification.
Also, thanks for the wiring diagram, but is it still a proper reference point if I am 12 v as opposed to the original 6v as is the diagram. Or is it basically the same just running 12v instead of 6? Thanks for the clarification.
Fleet Mechanic
Joined: Dec 2005
Posts: 1,603
Likes: 44
The fat terminal on the gen is Arm. the small one is the field. Doesnt
matter 6or 12vts just find the fat or 10gauge wire that goes to the fire
wall test it, if its hot thats the one that goes to the amp gauge. No doubt
its neg gr. now if it had an alternator.
matter 6or 12vts just find the fat or 10gauge wire that goes to the fire
wall test it, if its hot thats the one that goes to the amp gauge. No doubt
its neg gr. now if it had an alternator.
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Cargo Master
Joined: Aug 2010
Posts: 2,927
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From: Houston
If the generator still has the factory tag on it, it will say 6V or 12V. Otherwise, all 6V armatures I have seen use a rear bushing and all 12V armatures I have seen use a rear bearing. The journal on the 12V units is smaller to fit the inner diameter of the bearing. Unfortunately I don't have disassembled generators at my house to measure for you.
The main difference 6V verses 12V is the ground. 6V uses positive ground while 12V uses negative ground. When switching between the two you need to reverse the direction of the wire going through the ammeter and reverse the battery cable locations. I think all the other gauges work either positive or negative ground, you just need to provide 6V for them to not burn out. These people look to have a good 6 volt power regulator, but I have not used one myself: http://vintageautogarage.com/voltage...o-6-vo126.html
The main difference 6V verses 12V is the ground. 6V uses positive ground while 12V uses negative ground. When switching between the two you need to reverse the direction of the wire going through the ammeter and reverse the battery cable locations. I think all the other gauges work either positive or negative ground, you just need to provide 6V for them to not burn out. These people look to have a good 6 volt power regulator, but I have not used one myself: http://vintageautogarage.com/voltage...o-6-vo126.html
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Postmaster
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I think the PO had swapped over to 12v when he dropped the small block chevy in there. While I'm swapping in a 239 flathead on the way back to original, my intent is to stay with 12v. I'm definitely negative ground & have a new 12v battery ready to install. The generator/alternator issue has me confused and also realizing there's a little more involved than just hooking some wires back up.
I'm anxious to try and fire this thing and let it run for 30 seconds just to see if the motor is still good. If so, I could take a more methodical approach to getting everything hooked up for the long haul. Thanks for hanging in there with me as I try to figure this out. I've just got some kind of mental block
on this electrical stuff. It just doesn't come easy to me and sometimes it just don't come at all. 
I'm anxious to try and fire this thing and let it run for 30 seconds just to see if the motor is still good. If so, I could take a more methodical approach to getting everything hooked up for the long haul. Thanks for hanging in there with me as I try to figure this out. I've just got some kind of mental block
on this electrical stuff. It just doesn't come easy to me and sometimes it just don't come at all.
Junior User
Joined: Sep 2008
Posts: 90
Likes: 0
From: Whiting, NJ
If you're going to stay with the negative ground 12 volt system why not keep the alternator?
"One wire" alternators are inexpensive and they tend to charge at a lower RPM than the generator setup.
"One wire" alternators are inexpensive and they tend to charge at a lower RPM than the generator setup.
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Postmaster
Joined: Jul 2008
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If you're going to stay with the negative ground 12 volt system why not keep the alternator?
Mountain Pass
Joined: Apr 2010
Posts: 234
Likes: 9
From: Tuttle, OK
Speedway sells a one-wire alternator that looks like the stock generator and bolts into the stock location and uses the same belt. Easy replacement, but pricey $300+.
Cheaper alternative since you have the alternator would be to buy an alternator bracket for the flathead. About $60.
Cheaper alternative since you have the alternator would be to buy an alternator bracket for the flathead. About $60.
Mountain Pass
Joined: Apr 2010
Posts: 234
Likes: 9
From: Tuttle, OK
Oh by the way. My flathead has the alternator cinched into the original generator bracket. Works, but only marginally. The belt is out of alignment and has worn the bearings. I would recommend a purpose made bracket.
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