Fault code p2300 comes on intermittently and cuts out 1 cylinder. Code says rear coil voltage low

There may be one or more causes for the P0485 code. One is a faulty cooling fan. Another is that your fan control relay harness is shorted or open. Your fan control relay or fan control circuit may also suffer from a poor electrical connection.

The 3000 mule I have worked on has a coil, wire which screws into the coil and spark plug boot.
Do you have power and ground connection at coil.
You said you replaced coil did the wire and spark plug boot get replaced also.
If there is any question about the connection between the coil, wire and boot you might try removing the coil, wire and boot from back cylinder and placing on front. Swap them and see if you loose spark on rear plug after swapping.
Just a thought.

Your engine codes should only be in two digit numbers and you should not have codes that end with any zeros.check engine light should flash like count the flashes three flashes pause then 6 flashes would be code 36 then longer pause between codes then you have more than one code after a long pause it may flash 4 times then short pause then two flashes would be code 42 witch is engine coolent temperature high voltage a code 56 is fuel pump open load/short to battery or short to ground should start with one flash short pause then two flash meaning 12 then codes will repeat ,to start flash engine codes turn key off and on three times in less then 5 sec then leave on

Has the control system been scanned for fault codes? Do that first.

Most likely you water in one of the connectors, this code is for voltage high or voltage is low at the IAT sensor (air temp sensor in the air box) It could be the sensor connector that is at fault or the control unit back by the battery.

More than likely you have either a bad coil or the rocker arm has slipped off. Pull each plug, Check plug. If 1 is fouled, that cylinder is where the problem is. Check for spark on each cylinder, If one has no spark, replace the coil (there are 2). Replace only the bad one. Before replacing the coil, check for compression, if on is real low, pull off the rocker cover and check for valve action.

51 is a injector on #1 cylinder is stuck open.. will need to check wireing for damage first. 52 is cooling system fan issue.. fan is overload condition or maybe shorted to ground. Will likely have to chase wires to find issue.

Solid state ignition has a capacitor that must charge and when the right time comes a SCR will dump the charge into the coil to make a spark. There is a minimum voltage that is required to trigger the SCR and at low RPMs that normally is close to being not enough. Most likely you will need to change out that CDI ignition or check the coil in the magneto, it may need to be adjusted closer to the flywheel.

From Repair Pal:

Auto Systems and Repair

Engine Coolant Temperature Circuit Intermittent Our emissions expert has put together the following information about the P0119 fault code. We have also included diagnostic procedures you can take to your repair shop if the mechanic is having difficulty analyzing the code.
OBD II Fault Code

• OBD II P0119

Fault Code Definition

• Engine Coolant Temperature Circuit Intermittent

What does Mean?The Engine Coolant Temperature Sensor measures the rise and fall of the Engine Coolant Temperature. This provides critical data needed for the Powertrain Control Module (PCM) to control the Air Fuel Ratio, the Ignition Spark Timing, the cooling fans, and many components of the Emissions Control Systems. The Engine Coolant Temperature Sensor converts the coolant temperature into a voltage that is high when the engine is cold and low as the engine warms up.
Code P0119 indicates an intermittent voltage input from the Coolant Temperature Circuit to the PCM.

Carburetor on the side that's wet, need repair.