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**GregWeld** · #7 06-05-2010, 02:57 PM

You don't need any special harness.... in order to add a relay to the pump. I'll ASSume you don't understand what a relay does and how to wire one...

The 30 amp relay (should get a nice water proofed version from SPAL) is simply a switch... it gets one leg of 12V HEAVY gauge wire from a battery source - and one heavy gauge 12V GROUND... and on lighter gauge ground - and one lighter gauge 12V switched (ignition). So only 4 simple wires -- the light gauge wires are your control switch. You can choose to switch a relay either by switching the ground wire - or the 12V + wire... they don't care...

The PUMP is either wired with 12V + or 12V ground (-) -- I don't know if it's a two wire install or a one wire and grounded thru the case.

IF --- it's 12V+ wired and grounded via the case -- then that is the LOAD and is connected to the relay via the terminal #87 using heavy gauge wire (I'm using common numbering that is on most all relays) just look at the relay terminal side and each should have numbers next to them.

Connect #86 to your 12V + switched (ignition if thats the switch source)

Connect #85 to ground (any good ground)

Connect #30 using heavy gauge wire (preferably fused as well) direct to battery positive or a suitable heavy 12V+ source

IF your pump has a ground wire -- just use a heavy gauge wire and connect this to a good ground at the block.

Now your ignition switch only has to use about 5 volts and about a half an amp to switch the relay - which will then switch via the heavy wiring - your pump on. So the heavy gauge wiring is doing all the "work" and carrying the load (pump) and your ignition switch and it's lighter duty wiring is only running the relay (a switch) and carrying NO load other than to switch the relay.

This is all a "relay" is --- it doesn't do another thing -- it's just a switchable switch that is in the circuit to carry the work load. They should be used whenever you're going to switch something more than about 10 amps... such as electric fuel pumps - electric fans - high amp headlights etc.