Nate T.

It's probably a dry rotted spot in the line near the pump. 

I've never seen an electrical schematic for the Mule, but if you have one please post it.  Me and a couple guys here in the avionics shop will look it over

Better to have the drum stripped out than the axle or the rear end.  

The 550?  Dang I saw one on Amazon for $15. If anything just use the housing and swap old parts in.  

Fuel pump also.  Its vacuum operated so if the pump diaphragm is ruptured it can literally suck fuel into the crankcase.  The good news is there are some really inexpensive fuel pump replacements available.

It's easy to pass fuel through the carb if the needle valve is worn and not making a good seal.  

Plus your weight and any passengers plus fuel. 

Knowing how unscrupulous warranty people are, they'll probably say you overloaded the payload capacity which caused deflection in the axle.  

That kind of damage is the result of misalignment and/or corrosion issues from poor QC and defective parts.  If the alignment was off, from a bad bearing or improper assembly the gear would "waller" in there enough to wear down the teeth.  You would have to put a small block Chevy in your SxS and do burnouts every day for a year to grind those teeth the way they are if everything else was correct.  

Isn't there a transaxle or transmission bolted up to the motor? Could have a bad seal that is leaking fluid through.  

Hey no one is forcing him to work there, let him do what he wants.  We had a coupling like that gear at work strip out and looked exactly like your rear end there.  Except it was 60 years old with daily, 24hr usage.  

The back plate of the hub brake drum will interfere also if its bent out of alignment.  I had to adjust mine after some repairs with a mallet.

The gas caps have little silicone flapper disks in them that vent one-way.  When they start to deteriorate they get really sticky and ambient pressures aren't enough to break the seal.  The pressure you're sensing when opening the cap may be air rushing into the gas tank.  

I would suspect the gas cap not venting and creating a vacuum.  Seen it, fixed it.  Crack the gas cap loose and try idling then. 

OEM lights and not LEDs, correct? If that's the case those OEM lights draw a lot of current, probably in the neighborhood of 50w each.  The stator on an old Mule isn't that beefy to begin with, so you will get a significant voltage drop when the lights are on.  Maybe you don't really have an issue.  Or maybe you have a slight short to ground somewhere in the wiring with rubbed through wire insulation.  

Overcharging with a hot voltage >14.5VDC can damage battery cells.  You can also get low quality batteries fresh from the store.  Your hot voltage may have killed a new battery.  

Main jet issue.  Probably some tarnish or trash or fleck of gasket. This is a carburetor model, right?

No, but shouldn't be far from the ECU.  Little black cube that plugs into a socket.  Sometimes they're held in by a black rubber boot to insulate from bouncing and shocks. 

Read the wires back to the ECU, or maybe a relay, and then the relay to the ECU.  It could be a relay.  Those little Bosch relays do fail, but they're fairly cheap

A switch is just that - it let's voltage pass or it doesn't.  If the full-time on bothers you with a jumper, just put a $1.99 rocker switch inline with it.  Turn it on when you're ready to drive, off when you park it.  

Is it clicking like the old one?

Just jump it.  On a 2002 it really isn't worth gubmint safety parts

Awesome

Bud you've got yourself a pickle there after all that tear down.  Just keep it simple and troubleshoot each system in order.  Spark starts at the ECU with a signal sent to the crank/cam position sensor.  When that signal gets returned by the sensor (timing in the right spot for ignition), the ECU sends voltage to the coil.  The coil excites that voltage and sends it to the spark plug.  It's that simple.  The hard part is knowing where the wires and components are.  

Well then it could be the plug wire, fuse, wire issue, or crank/cam position sensor issue.  If you're not getting a position signal from the sensor, you won't get a spark