Positive ground alternators can be had but are extremely rare. Originally it was definitely positive ground like my '68 4020 that is now negative ground with an alternator and an ammeter.

The coil is wired backwards for negative ground, the positive post on the coil primary should go to the ignition switch through a resistor or resistor wire and the negative post should go to the points. I haven't checked the 4010 wiring, but on my 4020 an auxiliary terminal on the starter solenoid (S) applies full battery voltage to the 6 volt could for better ignition while cranking. That's why there is the resistor in the circuit. I know in the 4020 the location of the resistor changed at least three times between 1963 and 1969. One time it was in the ignition switch, then in the wire and mine was modified to use a ceramic resistor near the coil. The modification involved a Scotchtap that gave me lots of trouble but its long gone.

The best source of original information is the JD manual SM-2039 that covers 4010 and pre side console 4020 plus the operator's manual for the 4010. Like the changes in the wiring there were at least versions of the 4020 operator manual in the pre side console tractors because the ignition and starting switches plus the wiring harness was changed two or three times. Last I visited a Deere parts counter they could print a wiring diagram from their parts information.

The long skinny original battery was a poor choice giving poor cold cranking amps for its weight because of long intercell connection bars inside. I have mine modified to use a side terminal battery on the steps I built with much better cranking amps and much lower cost. The alternator has also improved the battery life considerably, but I've not had it running in several years. Need to work on that.

You need the operator's manual for the operating procedures for the LP tractors, they aren't as simple as a gas or diesel tractor.

Gerald J.