This is a schematic of your basic relay used ( SPDT (Single Pole Double Throw) Bosch relay, others may be laid out differently, but the numbers of the terminals should match - you can buy these at any decent car stereo shop, NAPA, or even Kmart, sold as a foglight relay. Supposedly Walmart sells amplifier install kits in their car stereo section, if you find 2 kits, buy the larger one).
For reference, the terminals are:

• 30 - feed wire
• 87A - Normally Closed (NC) terminal
• 87 - Normally Open (NO) terminal - the wire that the relay switches to when the relay coil is energized
• 86 - relay coil
• 85 - relay coil

• 30 - feed wire from battery
• 87A - Not used
• 87 - when cutting stock 12V pump wire, this is to the pump
• 86 - when cutting stock 12V pump wire, this is to the car
• 85 - ground

Note that the relay coil terminals can be switched, 86 can be ground, 85 can be power from the car.

Here's the 90 AWD pump wiring unplugged. Note the circled section - that is the end of the plug from the car side of the harness. While you can rewire with heavier wire all the way to the pump, including running through the pump assembly top plate, it is usually unnecessary. Splicing the relay into the wiring near the circled section should do fine, as you are only trying to remove the voltage drop caused by the tiny stock wire from the front of the car to the rear of the car. A foot or less of stock wire shouldn't drastically lower voltage once you are feeding it with the heavier wire and relay.

Here's a closeup of the 1G AWD pump assembly top plate. The circled black wire with a white stripe is the 12V supply wire to the pump. Follow this back through the harness to the plug shown in the pic above, and then match that up with the male part of the plug attached to the trunk floor to figure out which wire you will be splicing into.

Here's a closeup of the 1G AWD pump assembly top plate again. The circled junction is the one for the black wire with a white stripe, the 12V supply wire to the pump. If you feel the need to totally rewire all the way to the pump, you will need to carve that black crud off (it is tough going with a knife), and you will find...

that the junction isn't going to be that easy to handle. It is a riveted fitting, that runs through a plastic grommet to the underside of the pump assembly plate. You would have to drill this out and run a wire directly through the grommet, or find a brass nut/bolt to replace it with, and run new wire to the top of the bolt, sealing it with RTV or JB Weld, and installing a new in-tank wire with ring terminals on both ends.

Here is the underside of that grommet/riveted junction. If you drill it out and install a new brass or copper bolt through it, you could install a larger wire all the way to the pump. Again, I don't know if it is worth the trouble to do so.

Here's the pump assembly. The 12V feed wire is on the left. If you wish to rewire it all the way to the pump, this is the one you will have to deal with. Not worth the trouble in my opinion, but if you are an overkill kind of person, go for it.

OK, so now you have the wire located on the car side of the fuel pump harness plug. Now what to do? Simple - cut it in half. I suggest removing the rear plastic side panel, and cutting it back behind there, so you can mount the relay behind that panel. So you now have a cut wire, what to do. Well, you wire the relay in as I said above:

• 30 - feed wire from battery (Large RED wire)
• 87A - Not used
• 87 - when cutting stock 12V pump wire, this is to the pump (yellow wire in my picture, not stock wire color)
• 86 - when cutting stock 12V pump wire, this is to the car (long green wire in my picture, not stock wire color)
• 85 - ground (black wire in my picture, not stock wire color)