I have added an external electric fuel pump in my car wired through a relay that is being powered by a fused wire direct to the battery positive terminal.My concern is that this "main" power wire runs from right next to the back seat (relay hidden under interior panel to keep it close to pump) through the firewall around the engine bay to the battery on the passenger side of the car.As we all know the longer a wire the more resistance,etc etc.Plus I am not comfortable with it passing through the firewall (yes It has a grommet there), and I am trying to clean up the engine bay wiring.I would love to shorten this wire up and have it take power (to feed the relay) from the fuse block.My question is, is there any reason that I cannot run this wire right to the "BAT" terminal on the fuse block for the main power?See pic

Or does this wire NEED to go directly to the positive battery terminal?

 

I would also like to know what the purpose of these BAT slots are, as well as the IGN slots...

 

The BAT and IGN terminals are there for minor accessories that you or the dealer might add. The reason you wouldn't want to wire a fuel pump there, is because the circuit isn't really designed for that kind of load. If you're really worried about it, upgrade to a larger size wire. Dig around a bit, there are companies that sell a fuel pump hot wire kit, which use the stock wiring ot power a relay which is supplied voltage from the alternator.

The terminals in the fuse block are better for things car phones, gauges, stereo accessories (not amplifiers), etc. BAT is full time battery voltage, IGN is 12v switched. If you're going to use them for anything that really draws much power, you should probably just run power directly from the battery.

 

There are a few more that are useful as well (not for a fuel pump though).

RADIO - there's a slot there, gets power when radio is on.
LPS - there's a slot there, gets power when headlights are on.

Standard 1/4in spade connector fits right in these slots.