Why does Fuse # 2 & 18 keep blowing on 99 Ford Expedition

That's one that will require hands-on diagnostics. DO NOT put a larger capacity fuse in place of the blown ones - unless you want to walk (fire hazard). there's no cheap or quick fix for wiring problems. Look up the circuit diagrams, disconnect all components on the circuit, power the circuit. If the fuse blows with everything disconnected, it's a wiring problem in which you'll have to physically trace down the concern and replace or repair wiring. If the fuse doesn't blow, reconnect each component one by one until it does blow the fuse. My recommendation in this situation is to ask several people about their mechanic's reliability and seek that person out. BTW - electrical repairs are charged by the hour - you pay for how long it takes for them to figure it out and repair it.

Tracy's right, fuses blow due to excessive current in a circuit, caused by a damaged component drawing too much power or a short circuit, (bad Wiring).