New 5.7l Vortec safety oil pressure switch for electric fuel pump issues.

[Nauti St Tropez]

So ran into a problem installing electric fuel pump 3 way safety switch. There needs to be 12v cranking on 1 terminal to pre prime the pump before the oil pressure switch takes over. Problem is i only get 9 volts at solenoid. If i remove yellow/red from key switch and crank it there is 12v. I ran separate wire to solenoid and key same issue. Key switch was replaced do you think solenoid is bad? I had to repower this Mercruiser 5.7l vortec and the only way it came was with a electric fuel pump. I read 8 to 12v is ok for normal conditions at solenoid but this switch needs 12v cranking. Main harness connector good and all grounds are good. New battery cables as well as starter. 1992 Rinker Fieste vee.

 

[Scott06]

You are losing voltage during cranking or have a weak battery - by removing yellow res from the key you are removing the load, something down stream of this point is losing voltage during cranking. If youy just replaced the starter and cable double check the connection on the big starter lug is tight, all the power for the entire boat goes through here

 

[alldodge]

Main harness connector good and all grounds are good.

There is a connection which is not good. Think of the issue as a water hose with a restriction. Somewhere from the beginning to the end (meaning the ground back to the bat) there is some corrosion. It could be a contact in the 10 pin connector

Start post Red to 50 amp
50 amp Red/Purple to 10 pin
10 pin Red/Purple to 20 amp fuse
20 amp fuse Red/Purple to key
Key Yellow/Red to neutral safety
Neutral safety Yellow/Red to 10 pin
10 pin Yellow/Red to oil pressure switch and slave relay

And the ground in/out the 10 pin