How do you set the timing belt marks on a 1990 Ford Mustang?

If it is a V8 set the motor at top dead center #1 cylinder a the very top and the cam mark should line up with the middle mark on the crank sprocket or o degrees advanced.

it doesnt have a belt, it has a chain. there should be one or two lil dots on the chain and like a very small like on the sprocket, make the dots on the chain line up exact with the sprocket and your good

There is one mark (dot) on your came sprocket and one mark (dot) on your crank sprocket right about your crank "key" slot. Align those two marks (cam sprocket mark down, crank sprocket mark up). Now turn your crank 2 complete revolutions and verify that those two marks are in the same location that you originally set them. Obviously you will have to have the chain on. I just installed my millionth and one yesterday.