Engine won't shut off

[Gerkin]

Hi all. Hope everyone is having a great summer and lots of boating.
So this is a new one to me.
Twin rebuilt engines. (BBC 454s)
All new wiring, gauges switches. Basically everything is new.
When I fire the engines up, the Volt meter hangs around 12 until I give it a good rev of the throttle and then it jumps to the 13-14 range. When that happens, I turn the key to the off position and the engine will not shut down. I have to open the hatches and starve the engine to make it die. Also when I do turn the key to the off position the volt meter bounces all around between 12 and 14 like it is confused what is going on. Just like I am.
What is going on here? Where should I look?
Thank you for any and all help on this

 

[alldodge]

Let's start with are the Motors Volvo Penta, Merc, Crusader, etc ??
Next you have a serial number?

 

[Gerkin]

These are PCM 454s. I believe built near 1981

 

[alldodge]

ok, PCM will make it a bit harder to find wiring diagrams but will look

Moved thread

 

[Ifishmuskie2]

So your wiring to the key is wrong?

 

[Gerkin]

I have to assume wiring is wrong somewhere in the line. I will have to go out to the boat and then tell you where each wire is going

 

[alldodge]

I'm having a hard time finding an actual wiring diagram for PCM. I can find the owners manual and a so called service manual but neither show a diagram.

Get a pic of the back of the key switch, I'm wondering if it uses the same wiring as Merc

 

[alldodge]

Still nothing definite but think it would be same as Merc

 

[Bt Doctur]

How many wires are on the back of the alt? In most cases like this the diode in the alt is bad and backfeeding the ign system

 

[kenny nunez]

Take a close look at where the main battery cable is bolted to the solenoid on the starter. The battery cable could be contacting the bypass wire stud which will give a back feed . The wire may be black /purple.
Another possibility may be if you replaced the boost or slave solenoid with a automotive grounded base style could also give a back feed.