VERY dangerous imo to put through a switch, imagine the worst you are involved in a crash, the fuel rail or pipe splits/gets broken and you are unconcious you'll have fuel pumping out helping a fire along nicely, at least you'd be nice and warm!
What sort/make of relays have you been using, if the cheapo ones out of car shops some of these are very sun standard, what exactly is going faulty with the relays.
It sounds more like a connection problem than relays going duff, the 044 group a pump can only draw 18 amps at lockout, but as said add this to original wiring and you will have trouble, defo needs a rewire here and the fan.
If wanting security just cut into the wire and put a switch on number 85(earth/ecu) or 86 live(from ignition), 30 is input from battery, 87 is the output to the pump.
When I rewired my one I put the new relay up behind the rear seat, in the metal work around the "shelf" and seat back there is a nice 8mm hole each side just right to hold a relay holder, wire to this pop a relay in, so when at shows etc simply unplug the relay to stop pump.
It's essential for safety to keep some kind of auto cut out on it, like the ecu feed cutting it out when engine stops(as in accident) or via a impact cut off switch fitted to all later cars.
tabetha