DON'T use the chassis for earth, this misses the whole point of eliminating bad connections, take straight from battery so you have less power sapping connection points.
Despite what is shown the relay is NOT a spdt, it is a changeover relay which will do the job no problem, but a single pole single throw spst is more normal and found a bit easier,
polevolt.co.uk or vehiclewiringproducts.co.uk
The one MAJOR mistake above is the cable size, if you want to start the QE2 fne but massive overkill for this, if a fault should develope between cable and fuse it WILL torch your car, this 10mm2 cable carries 70 amps continuously is around £1.40 a metre but a std cable of either 44/030 3mm2 will carry 27.5 maps over double what the pump can use is plenty big enough and less than 1/3 the price, either that or thinwall 28/030 2mm2cable for 25 amps.
tabetha
tabetha