Sorry, I don't have a service manual for the Fourtrax 250, but the 250 did have an accessory plug. It wasn't the normal round accessory plug or outlet, it had two flat terminals like a plug that fits in a wall outlet in your house, but one was turned sideways. The rubber plug that is on it, pulls off and you wire that side to your accessory and that plug stays on your accessory all the time and you just plug it into the accessory outlet on the ATV. You have to have one of those plugs for each accessory that you want to use, otherwise you would have to take it off and wire it to each accessory each time you use it. To wire the plug up to an accessory you have to pull back the outer rubber cover and it will expose the two screws that your wires hook to. You have to feed the wires through the rubber plug first. They are marked with a "+" and "-".
To remove the headlight, just swing the two brackets out (one on each side) and pop the headlight off.