I've been looking at that schematic, but don't understand the OBD configuration. I think S108 is a voltage source, providing power for both the fuel pump relay and starter relay. I don't believe the fuel pump nor the fuel pump relay provides this power (as you mentioned).
I've looked, but can't find the origin of S108.
My apologies... i should'a chased S108 down, too.
The trick on chasing that down is the "(8W-30-18)" that appears under the S108 reference in the first diagram.
That's the page where it appears.
"S" means "splice"... which
usually means a wire goes to more than two destinations (i.e. has 3 or more terminal ends, be they source or sink).
And i fully agree with you: as drawn on the above and following diagram, i can't see how it would work... it appears as if the two relays are in series between the two "control" pins.
S108
must be a 12v power source from somewhere.
Here's 8W-30-18 that shows S108, and the lack of an off-page reference is the book's way of saying "this is all of it" (which doesn't agree with the Starter page (above), which does have an off-page reference, despite showing both BK/RD wires).
Adding to the fun is the 2004 ServiceManual, which has a typo using 8w-30-28 (which doesn't exist) in all of the -18 reference places. The 2003 manual (no in-tank pump) just drives only the starter relay from the ECU, like the "non-OBD" 2006 version.
If i were to simply
guess, i'd suspect
Fuse 18 .. Pin 1 on ECU connector C2!
That's a "fused engine control relay output", is Bk/Rd, and shows up as going into Pin 86 on the Fuel Pump Relay for OBD systems. (found by chasing BK/RD down the Connector Pinout lists...). It may also appear as Pin 4 on Fuse Block 1's Connector 4.
arrrggghh...
--dick
p.s.
added ... arrggghhh squared... so i went through all of the ECU connections shown in section 8w-30.
On page 8w-30-24 (OBD) they show the "fused output" arriving at pin 1 C2 from FB1 Fuse 17.
They don't
show a splice on that line... but i'd be strongly tempted (if i were tearing things apart) to see if an ohmmeter thought ECU plug C2 pin 1 connected to the starter and fuel pump relays (when the ECU, fuse 17 and both relays were unplugged, to avoid cross-contamination/confusion)