I also installed a dash light to indicate "ON". My Kubota has this and it saves me from having more hours on the meter than actual. See attached photo
I used a simple Radio Shack 12 V DC lamp assembly, part number 272-336. It comes with spades off the base. I made up two leads with spade and ring trminals. To take Gregs advice to avoid another circuit, I attached it to the horn. The horn is only active when the tractor is "ON".
This is the true idiot light. But hey, I bet I have saved several hundred hours on the KAMA's hour meter!
I'll say it again, this sure is a beefy tractor. I hope to get some seat time this week, I'v been busy installing my hardwood flooring this weekend.