by Bob Muller
Because my historic military trucks sit for long periods of time, I keep them trucks on a “smart” float charger so they always start. But, a few years ago in the autumn, I had a nagging suspicion that all was not well with the charging system on my 1944 Chevy G506. Trying to start it after having just recently taking it out, the Chevy just seemed to lack the power to turn over the starter like it should. The ammeter showed it was charging, so I didn’t think much more about it. But when I took it out the next spring, the ammeter no longer indicated it was charging. Thus began my journey into the world of 6-volt military charging systems.
We are experiencing the profound loss of many of our WWII vets. While many have passed, those who remain are no longer the resource they once were. My normal “go-to” guy, a WWII military vet, is now in an assisted living facility. While he truly wants to help, he just doesn’t remember. I only wish I knew half of what this man forgot! He knew WWII trucks inside and out and could fix just about anything he laid his hands on. Unfortunately, these indispensable resources that knew it, lived it, and fixed it are no longer accessible to most of us.
So, I turned to other members of my club. They gave a variety of potentially helpful hints and advice:
“Make sure you clean all your electrical contacts really well.”
“Polarize your generator.”
“Have an automotive electrical rebuilder test your generator.”
“Adjust the points on the regulator.”
With manual in hand, I tried each one of these; often, repeatedly. Every time I disconnected the wiring to check out the generator, I re-polarized it. I cleaned all the contacts. The generator bench charged just fine. The military voltage regulator appeared to be the culprit.
I contacted several rebuilders I had found on the internet who rebuild vintage regulators. When I mentioned it was military, they said they couldn’t help.
Early spring turned to late spring, and I saw the parade season go by without being able to use this truck other than for one very short local Memorial Day parade. With frustration mounting at being able to find — much less, fix — the problem, I decided there had to be another way.
I won’t say I am an absolute purist, but I do like to keep my trucks original to the extent I can. I know that you can convert from 6 to 12 volts, but it still involves a number of steps outside of the replacing the generator. Bulbs will have to be replaced, gauges require resistors, and while not difficult, it can be time consuming and expensive. Since “necessity is the mother of invention,” I discovered two alternate charging methodologies.
CHARGE AT 12, RUN AT 6
While talking to a mechanic friend, he mentioned he installed a 12-volt to 6-volt “ballast resistor” on his old 6-volt Ford tractor. He said, “It worked great.” He could start it off a 12-volt battery, but with the resistor on the line from the starter to electrical system, the output from the battery to everything else was only 6 volts.
He ordered one for me, but when it came, we noted it was rated for a max of only 10 amps. In doing some further research, we found that this is pretty much the largest ballast resistor we could find in stock. While it would certainly run the ignition, it would be challenged when trying to operate the lights plus any other additional electrical drain.
After some more searching on the internet, I found 12-volt to 6-volt transformers for sale with a 30-amp capacity. These are available on eBay for about $35 and nearly all are from Asian markets.
So what is unique about using these “step-down” transformers? The beauty of this approach is that everything on your truck stays 6-volt with the exception of the charging/starting system. You have the best of both worlds: You have the power and punch of 12 volts going to your starter, while maintaining the originality of the lights and the rest of the electrical system.
Installing a Step-down Transformer
Installation is easy. Here is what it entails:
1. Paint the transformer to match your color scheme and mount it on the fire wall of your vehicle. On my Chevy, mounting it under the Military Senior Oil Filter made it very difficult to spot without looking for it.
2. There are three wires: Ground, 12-volt in, and 6-volt out. Run the ground to a good ground on the engine block or frame.
3. Interrupt the wire that currently goes from the battery to your ignition. The 12-volt side of the transformer will attach to the starter side of that wire. Attach the 6-volt output to the end that continues on to your switch and ignition.
4. Replace your 6-volt battery with a 12-volt battery. Due to increase in voltage, you will not need the same cold cranking amps (CCA) as the 6-volt battery had. This will save you a few bucks, and your engine will turn over much faster.
5. Replace the generator with a Delco Remy “one wire” alternator. These are readily available online or at your local auto electric store. For most historic military vehicles (HMVs), a 60-amp is more than adequate. You will want a “10SI” (Systems Integrated) model that is self-regulating.
6. There are any number of brackets on eBay and parts stores that will allow you to mount the alternator where your generator was. Although a little more money, I liked the heavier duty model from Davis Speed Equipment. Painting the alternator in the same color scheme as your truck will help it to blend in. See picture of the bracket in this article.
7. Run wire from the alternator to the hot lug of the starter where the battery attaches. This should be a minimum of 12 gauge copper — preferably 10 gauge. There are a number of internet sources to get correct cloth-covered wire to fit your needs. I have purchased period correct cloth covered wire both on eBay and through Rhode Island Wiring. I do recommend always getting new wire as NOS wire can be corroded inside the sheath, and the sheath, itself, be deteriorating.
Note: As with all electrical work, make sure your terminal fittings are clean (sanded) and shiny for good contact. I like to solder on the terminal ends, when possible. This guarantees a solid connection that won’t weaken with time or vibration.
Once you have your alternator and transformer in place and wired up, you are good to go!
The first thing you will notice is that the engine will turn over twice as fast. This is of particular help with engines like the Chevy 235 that can be prone to vapor lock. Other than starting much easier, the rest of your electrical system, including actual ignition, is still 6 volts – nothing else is needed. The ammeter will not work without additional wiring, but I tested my output and satisfied all was working. Since then, I have not worried about it. Three years later and multiple parades, benefits, and events, the truck still starts like a champ — even in the winter.
Keeping it 6 Volts
At the same time I was resolving the issues with the Chevy, I was a few years into restoring a CCKW (a NATO return). The electrical wiring had been modified resulting inmultiple points that could cause issues with starting and charging.
Again, I like to remain as pure as possible, but if I can improve a system that will lessen the chances of a breakdown 25 miles from my house, I am going to look into it! The Chevy modification was working so well I decided to go for a similar approach on the CCKW.
In searching eBay for alternators, I ran across Howard Enterprises of Iola, Kansas. Speaking to Bill Howard, I found he does custom alternators both in the normal 12-volt and 6-volt configurations. For only a little more than a standard 12-volt, one- wire GM alternator as noted above, Howard can provide one in the same type frame in either 60-amp/6-volt or 100-amp/6-volt.
Mounting this unit the same as above will eliminate the need for the voltage regulator and keep the entire truck the stock 6 volts — and no need for a transformer. The voltage regulator can stay in place (but not in circuit).So, to most observers, nothing appears different from a wartime engine. The alternator in place of a generator would be the only noticeable feature. If painted OD or satin black like the other electrical components, it is rarely noticed.
The 60-amp unit is more than adequate. Remember, most of these generators were only 40-amp to begin with.
Typically, most of his Bill’s clients want chrome or plated parts, so I made a point to order it without the plating. That way,I could paint it myself — and the paint would adhere. I also got the larger pulley with it. This allows the alternator to run at a higher rpm at idle, thus charging at all engine speeds including a low idle. It is important to order the correct unit as to positive or negative ground. The early Chevys and GMCs had positive ground, while the majority of the late war models were negative ground.
Remember, DC systems run higher amperage, so your wire size needs to be up to the task. To be on the safe side, I use 10-gauge, woven copper wire. You can purchase this new with a fabric covering as original (I usually go for the brown or black cover). The dark, original-type wire is unobtrusive and certainly looks original when neatly run across the fire wall.
I recommend avoiding used or even NOS wire. Over time, corrosion can build up between the strands creating added resistance you do not want.
There are a number of companies offering cloth covered wire, but I have always had good luck with the harnesses and wire I have gotten from Rhode Island Wiring or Vintage Wiring.
Since those two adaptations, I have also converted a 1944 fire truck to the 6-volt alternator system. This truck has working spotlights, beacon, and siren (Federal “Coaster”) that really has the amp draw. Despite the heavy demand at times from kids and adults riding the siren in parades, it has performed without a hitch. You can’t do an easier, quicker conversion!
I, and my fellow club members, are fortunate to have a great support network. If anyone breaks down, club members are more than willing to jump in an make sure you get towed home or at least to a safe area. The only cost is usually some good-natured ribbing. Even with this network, having an ignition system you can trust when you drive in parades or at events makes it much more enjoyable and stress free.
Tips & Resources
12-volt to 6-volt Transformer
These are available on eBay for about $35. You will want to search for “Step down power converter”to find multiple suppliers. As these are likely to come from the Pacific Rim, be sure to check shipping costs and be aware it will likely take several weeks to receive. I picked up a second one so as not to get stranded if there were problems with the one installed. So far, no issues have arisen.
I have purchased battery to starter harnesses and variety of wire from Rhode Island Wiring and found their work to be excellent. They have a technical support line, as well.
Rhode Island Wiring Service Inc.
567 Liberty Lane, PO Box 434
West Kingston, RI 02892
Phone: (401) 789-1955
Catalog Requests: firstname.lastname@example.org
If you decide to go the route of a total harness rewiring, Vintage Wiring offers the most complete line of excellent harnesses for WWII and civilian trucks.
There are many variations of these that allow you to mount an alternator onto an engine designed for a generator. I tried the generic “fits all models” type but replaced it with one by Davis Speed Equipment. These are extremely well built, heavy duty, one-piece units that including an adjustment arm. Cost is a bit more at around $70 but well worth it. They are available in several vehicle configurations, but for the Chevy 235 or GMC 270 you would order the “10029’37 –’54 Alternator Bracket” and use that search string on eBay as well.
Davis Speed Equipment
1821 Melrose Street
Madison, WI 53704
eBay name: davisspeedequip
While there are a few places that manufacture these, I got mine through Howard Enterprises. He was a wealth of knowledge and experience and very accommodating to my needs and subsequent questions.
Iola, KS 66749
eBay username: billh6800
Bob Muller is a frequent contributor to Military Vehicles Magazine. An avid and active HMV collector, he lives in Delanson, New York.