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Need a Live Wire - Auxiliary Fuel Pump Wiring

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Old 04-11-2013, 03:16 PM
Stuart Dickinson Stuart Dickinson is offline
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Need a Live Wire - Auxiliary Fuel Pump Wiring

Hi Everyone,

Working on my 1992 F350 (single rear wheel) long-box crew cab. Just drove it from Florida to British Columbia pulling a 7000lb trailer. What an adventure but even at 200,000 miles, the beast just soaked it up!

I have a used vegetable oil conversion system + 1600 litres of veggie oil and I'm putting it on my truck. The 'parts' truck I pulled it off was running nicely so I know it works. Nothing fancy, has a copper coil + insulation under the front tank, running off a coolant loop. There is an in-line coolant/fuel line heat exchanger and an additional fuel filter, again, wrapped in hose running off the same coolant loop.

The tank selector switch is relocated to the engine bay, so the purge cycle should be pretty short, and it also has an auxiliary fuel pump just after the selector switch, which is wired to a toggle switch in the cabin. This is set up to activate a 12v relay which draws fused current from the battery.

I'm a reasonable home mechanic, and okay at electrics but I'm not as confident with that side of things.

I'm trying to figure out how to wire up the switch in the cabin to activate the relay and feed the auxiliary fuel pump. I removed the relay with all the other wiring intact, but the in-cabin was a bit of a mess because someone had added stereo etc.

I know that the 'middle' post on the relay runs to the switch, I'm assuming that I then need to wire the other side of the switch to a part of the wiring loom that has live feed when the key is on. Presumably then flicking the switch will close the relay and then feed the pump?

The only thing I can't figure is, there is also a feed from the RHS of the relay in the photo below, that runs into the wiring loom.

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Old 04-14-2013, 09:34 PM
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speedwrench72 speedwrench72 is offline
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the small wire is the relay trip wire,as you know,, the one on the left should run to the load (pump) the other on the right should run to a fused power source to supply the power for the pump when the relay is energized..if this relay is for a electric pump, this relay is possibly over sized...will still work... a smaller cube relay would allso work..the extra wire is probaly the PO geting power for some other device, and he is geting it from this point..
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