I agree. I converted my M1009 from 12 volt, BACK TO 24 volt. I had to get another alternator, starter and resistors/bracket. It really did not take that long, once I had all the parts. I was very fortunate, the PO did not cut any wires when he converted it to 12 volt. It starts so much easier, I can literally "bump" the key/starter and it will start, even after sitting all night in the high 20's.
That's probably because you were trying to push the amps needed to turn the starter with 12 volts in cables that were sized for 24 volts.
The starter needs the same amount of energy to turn the engine, whether it's running on 12v, 24, 48, or 480 AC 3 phase (if such a starter existed). The energy needed is determined by the job that needs to be done, not by the voltage being applied.
However, if we push that energy with a higher voltage, Dr. Ohm tells us we need fewer amps to get the same job done. P = I x E, or Power (watts) = Current (amps) times E (voltage).
If the job remains the same, and voltage increases, amps decrease. Works the other way, too. If volts DECREASE, amps need to INCREASE to get the same work done.
The problem with most CUCV 12v conversions is that they keep the same battery cables. Those cables were sized for lower amperage requirements, because they were sized at 24volts. If you want to do a 12v conversion correctly, you need to up-size your cables.
There are plenty of civilian 12v diesels out there that start just fine. But take a look at them - the cables are bigger than our CUCVs. Nothing wrong with 12v if you do it right, but most take the shortcut of using the same cables, and it works... Just not as well as it could or should.
If for some strange reason I ever decide to convert mine, I'll factor in the cost of bigger cables and either do it right or not do it at all.
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