Engine/Transmission (1998.5 - 2002) What is the third port on the fuel sending unit?

[Sticks]

Anyone know what the third port on the top of the fuel sending unit is?



This is the one that sticks straight up next to the wire connection and has the rubber cap on it.



Looking for a second place to plumb in a fuel pump.

 

[EricBu12]

that's an auxiliary fueling port... . I plumbed my aux tank from a fuel pump to that port. I imagine it is connected to the screen at the bottom but it works ok for a transfer... . a little slow but OK... . Be sure to have the clamp on tight... some have reported small leaks but mine is OK... .