I am bidding on a township job which obviously is going to be prevailing wage.
I have my co. hourly rate which is how we normally bid labor. Question is how do I come up with a labor rate for prevailing wage.
I know what the prevailing electricians rate is and the fringe benefit, but how does that affect my hourly rate for the company?

How did you come up with your companies hourly rate? Add up the wage & fringes (including SSI, workers comp & unemployment, after all, they are benefits), add your markup & that is the number.