I have a 90 amp one wire alternator going on the car.I want to put a circuit breaker on the charge wire to avoid a fire like I hasd last year. What size breaker should I use? Thanks for the help.

I would get one of these.
http://order.waytekwire.com/productdetail2/M50/46925/HI%20AMP%20MANUAL%20RESET%20100%20AMP/
And I use 75 amp relay turns on with oil pressure. So no circut is hot in the engine bay.

I just put a 100 amp continuous relay at the trunk and the alt. will run to it , then to the batt.
The relay is wired into the batt. disconnect so it will shut off all power from the alt when the disconnect is pulled.
I was told a couple different ways to go about this , but I wanted to isolate the alternator from all accessories and I think it should be plenty safe.
If it does barbecue a wire , it will only be the one , and this is #4 AWG.
If it does start to over charge , the relay should prevent it from doing any damage to anything else.