87 is the output and 30 will be the permanent live, i.e. what will be switched to power the pump, 85 and 86 are the relays inputs.

Typically the original relay is used as the trigger for the new relay, i.e. from 87 on the old relay to pin 85, 86 is a ground. Pin 30 should have your new FUSED live spur direct from the battery and pin 87 should be the output to the pump itself.

Remember to ensure the pumps ground connection has a good earth as well, this does not mean onto a rusty wheel well

Make sure to disconnect the batterys earth BEFORE you start any work!

Martin