Check engine light on and erratic speedometer operation.

bad or damaged body ground---chaffed/damaged wire or wire harness and bcm-[body control module ] going bad or harness damaged

I havent actually but from what your describing i'm leading towards a bad wire color code that caused you to mix up the wiring.

remove the harness and check the ground to be sure its coming from the harness.. connect 1 connector at a time to see which has the bad wire. once found trace all wires and replace the bad ones.

If the problem is the speedometer does not work, and if the gauges are ok, you may need a speedometer.
Does the odometer work ?
Is the check engine light on ?

You describe an electrical issue. First of all, how do you know the injector pulse is 'erratic'?
Is the ignition spark ALSO erratic? If so, how so? I need specifics, details regarding your description of 'erratic'. I can assume/presume you have experience/education/training in automotive diagnostics... ??

In my electrical/eagelectronics experience, you definitely have an electrical/electrodynamic problem/issue.

Tell me what you've done, diagnostically, to determine (isolate) the 'CAUSE' of this erratic injector pulse. What have you inspected/checked? What have you NOT inspected/checked?

Get back to me, then we can go from there.

However, first thoughts
The engine management computer (ECM/ECU/PCM) can cause/create the symptom you describe
The engine wiring harness also (chafed wires, bad ground circuits, etc.)
Malfunctioning senors (Crank Position Sensor (CKP), Cam Position Sensor (CPS),
Low Voltage Condition, etc.

Had the same problem. In my case, the wiring harness was scraping against the vibrating motor and wore through the insulation. This caused the computer to think the throttle position sensor was bad and the RPMs were erratic. The engine light came on and indicated TPS. A short time later, more of the wires became damaged and the engine started missing cylinders. My problem was at the top rear of the engine where the harness runs over a metal stud (right behind the valve cover). Check your wiring harness. Not an easy find until you actually look for it specifically.

have the shift solenoid checked out
Auto Zone will perform a free scan of the computer to dee which one is at fault

Polaris seems to have a problem with this issue. I had the same problem with my bike and was able to fix it . I found a bad resetable fuse link located under the front cover. It looks like a plastic case with wires at both ends. cut the case and check the condition of that part. I found it was badly rusted . I removed the part and wired in a 10 amp fuse with a holder. wrapped it up to protect it and the problem was gone. lights worked fine as well as the cluster. Ed.

?? Does it move on the road ? You could have a worn out CV joint that allows the transmission to free-wheel. If that is the case, replace immediatly, or the transmission differential will fail.