Weber carb install

[geezer101]

The preferred install method is using the live power to the fuel cut on the original factory carb set up as a trigger to a relay to run the fuel pump. It's the same wire you should be using for the electric choke swap on the Weber.

[SubGothius]

when i wire in the fuel pump with the relay would i be able to use the oil pressure switch as the trigger wire to send power from the battery to the fuel pump?

If you use an electrical relay, the trigger is turning the ignition key on, and w/ the oil pressure safety switch, that would interrupt the trigger circuit when there's no oil pressure -- i.e., there's two circuits going through the relay:

1. Trigger: Battery (+) > Ignition-on > Oil pressure safety switch > Relay trigger terminal 86 > Relay ground terminal 85 > Ground;
2. Power: Battery (+) > Relay power input terminal > Relay power output terminal > Fuel pump (+) terminal > [pump operates] > Fuel pump (-) terminal > Ground.

The stock oil pressure switch cannot be used as a relay or trigger by itself; all it does is complete a path to ground from the warning light -- i.e., oil pressure holds this switch open, so when there's no oil pressure the switch closes and completes the path from the single wire connected to it to the switch housing, which grounds to the engine block where it's screwed in.

Theoretically, you could use a DPST oil switch without a relay, so the two normally-open (N/O) terminals on the switch would perform the power-switching function instead of the relay, but this has some drawbacks:

• No power to the pump while starting. This may be fine if you drive the truck daily, but if you let it sit long enough, you may need to reprime the fuel line by shorting the two leads at the oil switch together (or install a momentary switch to do this) to run the pump manually for a bit before starting;
• A permanently-live wire running around the engine bay from the battery (+) terminal to the oil switch on the other side of the engine, so at least be sure to put a 10A fuse on this line right at the battery end, and route this wire well away from any moving or hot-exhaust parts (probably route it along the inner fenders and upper firewall). You'd also have some power drop to the pump due to the extra couple yards or so of wire this adds to the power circuit between the battery and pump.

The preferred install method is using the live power to the fuel cut on the original factory carb set up as a trigger to a relay to run the fuel pump. It's the same wire you should be using for the electric choke swap on the Weber.

That's one way of doing it, but IMO it's simpler and functionally-equivalent just wiring up the relay manually, since the ignition-on (+) terminal powering the coil is right there next to the battery anyway.

[Not Billy]

the way you just laid it out makes it so much simpler, thank you.