K54FROG,
I did mine a little bit different than Mahindra55, but mine works similarly. Mine can be operated whenever the ignition key is ON. The headlights/tail lights do not need to be on.
My lightbar switch activates a relay, which applies power to the light bar. Although a switch could control the lights, the relay will take a heavier current load than a switch, and the switch line can be relatively light wire -- which is a lot easier to run through and under the tractor frame.
Walmart had a nice lightbar wiring kit for about $10 that included a lighted switch, a fuse holder, a relay, and a wiring harness.
The 2015 and 2615 tractors have an auxilary +12 volt line at the base of the ROPS bar. It comes from the fuse panel located in the engine compartment. It is activated whenever the ignition key is ON. In my experience, many newer tractors have an auxilary line similar to this. It now connects through the relay contacts to my new light bar.
I was originally going to connect a fused line, for the switch circuit, directly to the positive (+) side of the battery. But, I found it easier and more convenient to connect to the +12V stud on the alternator. On these tractors, it connects directly to the battery.
So, I connected a fuse holder to the alternator. The other end of the fuse holder wire was routed with the existing wire harness to the back of the tractor. I brought it up to the base of the ROPS bar on the right-side fender. It connects to one side of my light bar switch. The other side of the switch connects to the relay coil.
I did not add surge protection diodes across my relay like Mahindra55. It is a good engineering practice to do so, but the impedance is so low on that line, I didn't feel it was necessary.
I picked up frame ground (battery negative(-)) through bolts at the rear fender. I mounted the switch with 3M tape in a protected area, on the fender, near the base of the 3PH adjustment lever.
I've attached a quickly hand sketched diagram.
I was going to take more pictures of how I did mine, but it is dark, very windy, and uffda-cold at only about +10 degrees F. Don't be afraid to ask for more clarification if this doesn't do it. It will warm up one of these days.
Knute