1952 Massey Harris 30: 6-Volt to 12-Volt Negative Ground Conversion

The 12-volt negative ground conversion on my 1952 Massey Harris 30, narrow front, is done. I used a one-wire 63-amp Delco 10SI alternator off a squarebody Chevy, made a new bracket and moved the bracketry about 3/4 inch forward. I reused the original 6-volt generator pulley, kept the original Auto-Lite starter, and put a new 12 volt 1 ohm coil in with an external resistor.

I really should have done this one a long time ago, I’ll put a video of it starting on 12V below, it starts so great now. There is no comparison from 6 to 12V! Now that it starts much better, it’s actually become much more enjoyable to just fire up and take it out for a drive. I have a pull behind PTO finish mower for it which will likely be the next project on the tractor.

Watch the Complete Massey Harris 30 Conversion

This long-form video documents the complete Massey Harris 30 electrical conversion, including the move from the original 6-volt positive-ground system to a 12-volt negative-ground system, alternator installation, updated wiring and final testing.

Why I converted my Massey Harris 30 to 12 volts

I often had issues starting it on 6V as a new battery would only last for a few cranks. Battery discharge was also a problem when left sitting. Last issue would be the fact a freshly charged 6V would not have a ton of power to actually turn it over. It seemed to have not enough power to really turn it over and it would have a hard time catching. Often I would just hand crank it.

Charging was the other half of it. The original 6V generator would not charge until higher RPM, and this tractor idles around 500 RPM, so at idle it was not doing much.

Why I did the carb and fuel work first

I chose to do this swap after everything had been run through this spring: carb clean, fuel tank clean and liner, fuel filters, plugs, etc.

If you are on the fence about doing this swap, I highly recommend doing it as the last step, after carb and fuel issues.

Main parts used

Part	What I used	Notes
Alternator	One-wire 63-amp Delco 10SI, off a squarebody Chevy	Chose 10SI to avoid having to externally excite it
Alternator pulley	Original 6-volt generator pulley, approx. 2.5 in	Correct shaft size, correct groove for the 1/2 in belt
Belt	B41 industrial V-belt (B-section)	1 inch larger than the factory belt
Bracket	New bracket made for the 10SI
Upper mount	3/8 in x 1.5 in Grade 8 bolt, SS round tubing spacer approx. 3/4 in	Spaced forward rather than bending a new one
Lower mount	3/8 in x 7 in Grade 8 bolt, SS round tubing spacer approx. 5 in, extra thick 3/8 in washers
Charge cable	#6 DLO cable, good for 65+ amps
Coil	Steiner ABC348, 12V “HOT” 55,000 volts	Shown as internally resisted at 1 ohm, must be used with an external resistor
External resistor	Steiner ABC366, universal 12V 2-terminal
Starter	Original 6V Auto-Lite, reused	Runs fine on 12V
Starter switch	Original heavy duty, still on	I have a spare

Installing and aligning the Delco 10SI alternator

I used a 1 wire 63A 10SI GM alternator off a squarebody Chevy and made a new bracket. I chose to go 10SI to avoid having to externally excite the alternator.

With this alternator, the bracketry had to move 3/4″ forwards towards the crank pulley. Upper alt mount got spaced forward with some SS round tubing and a longer 3/8″ x 1.5″ grade 8 bolt as opposed to bending a new one. The bottom mount I used a 3/8″ x 7″ gr 8 bolt and SS round tubing plus extra thick 3/8″ washers.

The best plan of attack with this system is to do the upper alt mount first, and straightline the alt down to measure the spacer length. I ended up with an upper spacer at 3/4″ and a bottom spacer at 5″.

One thing to plan for is the belt. The 10SI Alternator ended up sitting out farther than the OE Generator did, so the factory belt would not work. I ended up running a B41 industrial V-belt, which is 1 inch larger than the factory belt. When you go to replace it, ask for a B41 industrial V-belt.

Choosing the right pulley for the 1/2 inch belt

The pulley that comes with the 63A 10SI alternator is for a smaller belt and won’t fit the 1/2″ belt. We put it on first, just to test the size of the pulley as it was a 2″ pulley. It did charge off idle really well, but the bad news was that you’d be unable to use it for longterm as the 1/2″ belt would not be sitting inside of it and could slip off at anytime.

I tried to search for a 17mm shafted 2″ pulley for a 1/2″ belt, but had no luck locally. After searching for a bit, we decided to try the original pulley off the 6V generator. It was the correct size shaft, however it was slightly larger at 2.5″. The generator itself went in the garbage, the pulley is the only part of it still on the tractor.

My concern with going larger was the pulley ratio and if it would charge at idle.

Will it charge at idle?

For reference, the 4 cyl Continental in this tractor is max RPM at 1800, and idles around 500. The crank pulley is a 6″, the alt pulleys tested were 2 and 2.5″.

• 6 ÷ 2.5 = 2.4:1
• 6 ÷ 2 = 3:1

Engine speed	2.5-inch pulley	2-inch pulley
500 RPM idle	1,200 alternator RPM	1,500 alternator RPM
600 RPM	1,440 alternator RPM	1,800 alternator RPM
1,800 RPM maximum	4,320 alternator RPM	5,400 alternator RPM

The 2 inch pulley spins the alternator 25% faster than the 2.5 inch pulley at every engine speed, which improves low-speed charging.

On initial startup at idle I saw the voltage slowly going up via my multimeter, so I can confirm this setup will charge at idle. Slowly albeit, versus the 2″ pulley. Luckily for me it charges off idle which was my main concern, versus the original 6V generator not charging until higher RPM.

Coil and resistor

I used the Steiner 55,000 volt HOT coil, part ABC348, which was shown as internally resisted at 1 ohm. At that resistance it must be used with an external resistor. The resistor I used is the Steiner ABC366. The resistor I was able to bolt up directly to the coil’s bracketry using #10-32 hardware. The resistor is basically bolted through with the bolt that tightens the bracket to the coil. Pretty easy if you ask me.

If I could do it again, I should have ordered the internally resisted 3 ohm coil, part ABC6158, which would have avoided using the external resistor. Both coils are the same price too, so it would not have cost me any more and I would have saved buying the resistor.

Oh well, live and learn!

Running the original 6V starter on 12V

Original starter runs fine on 12V but I would recommend avoiding any excessive cranking. While it is an old Auto-Lite and built pretty heavy duty, I’d hate to burn it up.

The original heavy duty starter switch is still on, I have a spare if it chooses to burn up.

Wiring and fuses

The alternator was wired up to the battery using a #6 DLO cable good for 65+ amps. If you choose to do this swap, you could get away with a smaller alternator if not running lights or any accessories. Steiner lists a mini 40A alternator which would have been fine for this application but I already had the 63A alternator available.

I’ve attached my full wiring diagram here for your reference.

Please note that the factory wiring produced on this tractor in 1952 did not come with fuses, hence why I did not show any inline fuses on the diagram. Depending on your use or application, you may want to consider adding fuses.

By today’s standard, the key switch wire from battery positive should be fused with 15A, and fusible links could be used on both alternator and battery wire to starter. The main problem with the old tractors is there is really no good place to put any fusible links on while retaining a factory like look.

I chose to omit fuses on my tractor as it is mostly used as a showpiece and is not out working for hours at a time.

What I would do differently

Order the internally resisted 3 ohm coil, the ABC6158, and skip the external resistor. Same price, one less part on the tractor. That is the one I would change.

I’m still searching for a “period correct” voltmeter for the tractor but for now she’s good to go!

Full build thread on the forum

The complete build log is on the FullSizeChevy forum with the wiring diagram at full resolution, the wire gauge legend, more install photos, and a spot to post your own conversion.

1952 Massey Harris 30 — 6V to 12V conversion build thread

If you have done this conversion on a Massey, or you know where to find a period correct voltmeter, post it in the thread.

Common questions

Is a Massey Harris 30 positive ground from the factory?

Yes, 6 volt positive ground. Going to 12 volts means flipping to negative ground, which is why the battery negative goes to the transmission or engine block on my diagram.

Will the original 6 volt starter work on 12 volts?

Mine does and I kept it. Just avoid excessive cranking on it.

Will a one wire 10SI charge at idle?

Mine does with a 6″ crank pulley and a 2.5″ alternator pulley, around 500 RPM idle. I watched the voltage climb on my multimeter. Slowly, but it charges. Your ratio will be different, so work out your own before you pick a pulley.

Do I need a ballast resistor with a 12 volt coil?

Depends on the coil. The ABC348 I used is 1 ohm and needs the ABC366 resistor with it. The ABC6158 is 3 ohm and does not need one. Check the resistance before you order.

Should I add fuses?

The 1952 factory wiring had none, so my diagram has none. By today’s standard you would fuse the key switch feed at 15A and use fusible links on the alternator and starter cables. Depends on how your tractor gets used.

Can I reuse the original generator pulley on the alternator?

On mine, yes. The pulley that came on the 10SI was for a narrower belt and would not hold the 1/2″ belt. The original generator pulley had the right shaft and the right groove, just 2.5″ instead of 2″. Check your shaft size and belt width first.