First thing to check on the steering is if the steering column grease fitting has been greased. That fitting gets missed a lot. It's hard to get to and often requires the removal of the carbs to access. You may have to take a heat gun to heat up the shaft to soften the old grease to allow new stuff in. To check, lift the front of the sled and turn the bars. Is the effort difficult? If so, check the shaft and lube. Lube all the heim joint ends with oil while you're at it. If it's loose, look at the skis/wearbars. If there's excessive lengths of carbide on the skis, that could make turning harder.
If that maintenance had not been done, it's likely that both clutches need cleaning/service, as well. Check the sheave faces in the primary for belt residue, a black ring means rubber build-up on the primary isn't making good contact with the belt and the belt slips instead of grabbing. Sometimes it gets bad enough to require a scraper or knife. Don't gouge the aluminum and finish with a roughing up of the clutch with a green scotchbrite pad or sandpaper. Look at the sides of the belt as well; old, glazed rubber on the edges will not grip very well either.
For the light issue, I would start with all the grounds. It could be you are losing contact. Second thought would be voltage regulator.
Nice of you to get your dad into sledding, hope it gets better so he enjoys it!!