I remember trying to potty train my autistic son at age 4. That is when Pull-Up pants were new on the market. I felt that they just gave him reason to keep potty in the 'diaper' feeling panty. So I got cloth pants and he seemed to get potty trained real soon. Not sure, but I may have had him start washing his own undies too after messing them. He had a slight fear of water, but chores like this and having him mop the bathroom floor(very small) seemed to be a good discipline to help him take consequences for his negatives actions whatever they were. I believe a staff member @Lighthouse Community Christian School helped me to recognize the need to accomplish this.

I would show my son what to do when it's time to go potty. He was really scared about it at first. If he's scared, DO NOT push him to do it. It will only make things worse. Try getting a potty that you can keep in a room with a tv. Give him a snack and let him watch his favorite show, while on the potty. He will be too into what he's doing and eventually go. If he realizes what he did and gets upset, just praise him and give him a reward. Stickers are good. If he only goes very little and wants to get up, let him. Keep trying that same routine over and over. Good luck ;)

There is a good video called "Once Upon a Potty". We picked it up at toys r us. There's one for boys and one for girls because it shows a little cartoon kid with no pants on. It walks them through the whole process of going from diapers to using the potty with a cute song and there's a book that goes with it too if you wanted to bring that into the bathroom to show him the pictures while he's in there.
Personally we didn't do the whole potty in front of the tv thing because my children make don't like change at all and I was afraid it would be a huge battle to stop using the potty in the living room and move to the bathroom so we just did everything in the bathroom.