Best why to find out what should be on a motor is look up the serial number at a place like BAM
Here is your motor, look at Wiring harness and electrical components link
https://www.mercruiserparts.com/4-3l-gen-2-bbl-gm-262-v-6-1998-1
Never did one like yours, but everyone I've seen/done the center cap has to come off first. I zoomed in on center cap and don't see a wire snap ring, but maybe. Try pushing in in the center of the cap and see if it moves down and away from the outer collar.
If this doesn't happen the the cap...
Being a 2004 it should by regulation have a why to gain access. If there is carpet on the deck look for an inspection plate under it. Might be screw down type but might just be a plate
The trim pump gets power from the starter post. Look for red wire feeding pump thru a fuse on the pump
Fuel pump is on port side behind the motor mount.
There are 3 fuses on top the motor and 2 relays. The Main power relay turns ON and sends power to FP and motor/ECM
Your tie offs are incorrect.
The way it currently is the boat can move FOR and AFT which will break the whips. You need more lines to keep the boat from moving
https://www.rjmachine.ca/wp-content/uploads/2017/07/Wooring-Whip-Installation.pdf
It doesn't change with rpms so its not in the motor or drive. If it did then it could be
It over heated so might be the exhaust shutters in the exhaust but it's kind a loud for something like that
This could be the issue, tank pickup is in the rear
Fill as FT mentioned, then no need to crank just cycle key until fuel shows up without air. Fuel pressure gauge with drain tube is good for this, but can be done with screw driver
