Why won't my 2001 Kawasaki Mule 4010 Trans 4X4 go any faster than 16mph??? It runs, idles and accelerates without any problems. The top speed set from the factory is 25mph.

here is service manual look into cdi -plug as possible problem use trouble shooting guide -------- https://manualzz.com/doc/57493589/kawasaki-mule-3010-trans-4x4-service-manual

Question moved from Cars and Trucks.

Wiring diagrams in the link.

https://www.google.com/search?q=kawasaki+mule+fxt+le+fuse+box+diagram

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Something is shorting to earth on the brake lights.

Get a pack of fuses.

Remove left side bulb. Brake, does is blow the fuse?
Remove right side bulb. Brake, does it blow the fuse?
If yes to the above, it is the light fitting or wiring rubbed through to that light.

If no, it is the switch or wiring to the switch on the brake pedal.

https://www.google.com/search?q=4010+4x4+diesel+mule+blows+fuse

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I assume there is only ONE fuse, since you are not specific.
The solution therefore is just hard work and long hours with your ohmmeter disconnecting wires and tracking it down one wire at a time.

https://www.manualslib.com/manual/803081/Kawasaki-Mule-4010-Trans-4x4.html?page=37
You did not say what model you have
https://www.kawasakimotorcycle.org/forum/kawasaki-atv-mule/152674-2012-diesel-mule-4010-no-power-steering.html
https://www.kawasakiforums.com/forum/general-tech-9/kawasaki-mule-3010-trans-4x4-640/

Coil pick up runs the fuel pump also so u need to check the primary and secondary coil

16.5 foot pounds

First is the engine Diesel or Gas?
if it is a diesel engine it has almost got to be a compression or fuel problem if it is a Gas engine it can be a valve adjustment, fuel, compression, or spark problem

Sounds like a bent axle.... or something in the rear differential. ...the heat generated by the bent axle will cause all the clearances to disappear!!!