PCM 351 Main Relay Wiring

JDusza

Ensign
Joined
Apr 21, 2009
Messages
934
I'm bringing a 351 back to life and I would like some help with the main relay Wiring. On the face of the rekay are the letters S and I. The wires I have are:
Large diameter red with large ring terminal Small diameter red with large ring terminal
Large diameter black with large ring terminal Small diameter lack with small ring terminal
Small diameter red / yellow with large ring terminal Small diameter yellow / red with small ring terminal
Small diameter white with small ring terminal
Thank you,
J
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,464
I would like some help with the main relay Wiring.

Ayuh,..... What do ya mean, Main relay,..??

Is this the starter solenoid, or a slave solenoid,..??
 

JDusza

Ensign
Joined
Apr 21, 2009
Messages
934
I'm talking about the relay that's behind the intake cover. It is round about an inch-and-a-half in diameter and rather stubby. It has 4 lugs two large two small. It is thre main distribution for power. It takes the battery input and distributes it to other accessories and as the solenoid or relay it switches voltage and high current over to the starter. It is on a bracket along with the circuit breaker. Little red button.
 

hal2814

Petty Officer 3rd Class
Joined
Feb 22, 2006
Messages
92
Sounds like you're talking about the starter solenoid. If so, S is start and I is ignition. Those should be the small terminals. How it's wired depends on your ignition system and your starter. On my PCM the S goes back to the ignition switch via the neutral safety switch and low gauge cable runs through the large lugs from the battery to the solenoid and then from the solenoid to the starter. I is unused for my setup. On my boat ignition wiring goes straight from the ignition switch to the ballast resistor and on to the coil. But PCM ignition systems vary a lot based on age and even what manufacturer is using the engine (mine is an 83 Ski Nautique).
 

Bondo

Moderator
Staff member
Joined
Apr 17, 2002
Messages
70,464
Ayuh,.... I'm sure pictures might help,....
 

JDusza

Ensign
Joined
Apr 21, 2009
Messages
934
Well, not as easy as I hoped. Maybe I'm wrong, but I would call the starter solenoid (relay) the one that's on the starter to throw high current to the device and drive out the pinion. The solenoid I'm talking about IS the one that switches high current power (fat red) from the battery to the starter (fat black) and via the thinner wires, sends low current voltage out to "stuff". It is indeed the one with S and I on it.
I was hoping not to have to trace back to the dash but , ...
I wasn't caring about each wire's function as what color wire go to what terminal on the S / I solenoid. Could you be telling me PCM uses different color wiring across different products? Manufacturing cost driver. Not to mention a flaming departure from industry convention.
I guess I'll take a couple glamour shots....
This one's a '92 BareFoot Nautique (V-drive), 351 HO.
Thank you,
J
 

hal2814

Petty Officer 3rd Class
Joined
Feb 22, 2006
Messages
92
It's not easy because there are two different styles of starter. The starter that likely came with that boat is a one-wire direct drive starter. It's wired as I explained above. (I believe yellow with red stripe is the wire from the neutral safety switch.) If it's a gear reduction (two wire) starter, the typical wiring is for both low gauge cables connect to the same side large terminal (doesn't matter which side) and the S has a wire coming in from the neutral safety switch and a wire that goes out to the solenoid on the starter. That wiring basically bypasses the external starter solenoid relay since with a gear reduction starter it is not necessary and would just add an additional point of failure.
 
Top