I have a 1958 Ford 641 with original 6v system. The charging system is giving me fits. Every time I start it, I have to jump the voltage regulator terminals to get it to charge. I'm considering converting to 12v alternator system. I don't want to lose tach function. Suggestions?
Ford 641 12v conversion
- Thread starter MoBill
- Start date
Roadworthy
Elite Member
It sounds like you need a new voltage regulator. Is your tach driven by cable from the alternator or from the transmission? If the tach and hour meter are driven from the transmission there would obviously be no problem. For what it's worth I note the six volt models were positive ground while the twelve volt ones had gone to negative ground.
I've replaced the voltage regulator but the charge light still stays on when I start it unless I jump the terminals to polarize the generator. It's not a huge issue, but I'd just as soon not have to open the hood and reach in and jump the regulator every time I use the tractor. I've even thought of wiring in a momentary contact push button switch to do the same thing.
My tach runs off the back of the generator. I seem to remember seeing a 12v alternator conversion kit with a tach drive on it but I can't remember where I saw it. I imagine I could get an electronic tach and hour meter, but I'm trying to keep it as simple as possible.
My tach runs off the back of the generator. I seem to remember seeing a 12v alternator conversion kit with a tach drive on it but I can't remember where I saw it. I imagine I could get an electronic tach and hour meter, but I'm trying to keep it as simple as possible.
I'll have to double check, but my recollection was that when the light is out, I'm getting about 7 volts at the battery. I don't think I've checked voltage when the charge light is lit.
This all started when I got the tractor from the previous owner. When I originally got it, it had sat for a long time and the battery was in marginal condition. After charging overnight, it would start the tractor and charge normally. When it was running, the light would go out as it should. I decided to replace the battery and I installed one without polarizing the generator and found it wasn't charging at all. I then replaced the regulator and jumped it to polarize the generator before starting per instructions I found multiple places on the net. Ever since, it will charge if I jump the regulator after starting the motor. Maybe I got a bad regulator?
As I recall, the alternator kit I saw at one time was advertised as suitable for my tractor. I understand that when everything is working correctly, the original 6 volt system is perfectly adequate and I wouldn't think of changing it if everything was working correctly.
This all started when I got the tractor from the previous owner. When I originally got it, it had sat for a long time and the battery was in marginal condition. After charging overnight, it would start the tractor and charge normally. When it was running, the light would go out as it should. I decided to replace the battery and I installed one without polarizing the generator and found it wasn't charging at all. I then replaced the regulator and jumped it to polarize the generator before starting per instructions I found multiple places on the net. Ever since, it will charge if I jump the regulator after starting the motor. Maybe I got a bad regulator?
As I recall, the alternator kit I saw at one time was advertised as suitable for my tractor. I understand that when everything is working correctly, the original 6 volt system is perfectly adequate and I wouldn't think of changing it if everything was working correctly.
John0829
Veteran Member
The 641 tach is driven off the hydraulic pump mounted on the back of the engine, most all conversions us a delco 3 wire alternator available everywhere. Simple to wire, there are thousands of wiring diagrams and how to's on the web. If you do convert to 12V I suggest you remove the ignition resistor and replace the coil with a NAPA IC14SB, it has a built in resistance for use on a 12V system without the in line one and saves a lot of headaches.
John0829, You're absolutely right. I feel like an idiot. I'm writing about the 641 and thinking about my 3400, which does have a generator driven tach. Your post definitely simplifies things. Right now, I'm trying to decide if I should try another regulator and leave the 6 volt system intact, of if I just convert to 12 volt.
JethroB
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Many years ago I converted my Willys Jeep from 6v pos. to 12v neg. and kept the generator (changed out to 12v) and kept the 6v starter. I’m no expert but the generator seems to be my weak link due to it’s poor output at low RPMs. The 6v starter on 12v is the winner here as it really spins that engine. 
Just have to be care not to overwork/overheat the starter. No tachometer involved though.
Just have to be care not to overwork/overheat the starter. No tachometer involved though.
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WranglerX
Elite Member
Voltage dropping resistor or solid state 12V to 6V converter....
Maybe...
And maybe something like this to replace generator...
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Dale
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John0829
Veteran Member
Or find a re-pop that is made for 12V
RickB
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Yes, replace the coil. But there is no resistor to remove. No matter how you deal with the voltage change your fuel gauge/sender combo won't like the polarity change.