Being this is a GSI and also applies to the GI, you do not use a shunt.
The computer controls the timing. To put the system in base timing mode you need to find the Data Link Connector located in front of the engine on top, it is inside a storage cap. You then jumper two terminals with a small...
I think the wiring diagram that Bruce58 posted is for a carbureted motor, it would have one pump. The OP Leedanger stated they have the 5.7 GSi PWTR, which would have the fuel injected TBI system with the two pumps.
The ECM controls the pumps, I believe the relay should have constant 12v.
It is a drain hole, no o-ring in that groove and pointing down.
VP states that if this hole is blocked it could prevent water from draining out when you winterize your boat and could cause damage from freezing.
That is the correct location of the o-rings but do not reuse the o-ring next to the threads. That o-ring has taken a shape and you can see the tearing of the material.
When you reassemble, lubricate both o-rings with motor oil and put the second o-ring on after you put the bolt through the housing.
The threads on the impeller is a possible clue,
You may need a 1/2 x 20, 9/16 x18 bolt or a specialty tool to match the threads to press the impeller off of the shaft.
Also don't loose the little o-ring that's stuck in the screw hole.
Probably there is water in the bourdon tube inside the gauge, the water must have froze and expanded the bourdon tube and cause the gauge to wrap around.
