How to test shift interrupter on a Mercruiser?

[matt167]

Tried to fire my boat up yesterday ( it’s getting close ). Engine last ran in 2022 in the donor boat but it ran pretty well. I couldn’t get it to fire.. I quick stuck a new condensor in it and cleaned the points as best I could with what I had. and then later jumpered 12v to the coil from the battery but got no sign of life. Now I know the points need replaced and I have them but I didn’t have feeler gauges with me, nor a test light but I think I should have got a cough out of it. I’ll stick the points in it sometime this week

The interrupter is free and the pin doesn’t stick but could it be stuck grounding? If the switch is grounded, than even the jumpered power won’t matter

 

[Chris1956]

Gee, you might tell us the engine and year.

Can't you simply disconnect the ground wire to the interrupter?

 

[matt167]

Oh sorry it’s an ‘86 3.0L with the old style interrupter switch. Forgot to put that in there. I guess I could pull the wire off. I didn’t want to touch it as the switch is NLA, with the old wires ( provided it’s good )

 

[dingbat]

Pulling the ground will not tell you if the switch is shortened internally

Check for continuity between the switch input and output while operating the switch

 

[matt167]

Pulling the ground will not tell you if the switch is shortened internally

Check for continuity between the switch input and output while operating the switch

I’ll have to grab my DVOM from work and tackle it. I would almost tow the boat with me to work and work on it at the dealership after work but idk if they would like an 18’ boat in the parking lot all day

 

[Chris1956]

So you will take the mountain to Mohammed?

 

[matt167]

So you will take the mountain to Mohammed?

Kinda. I have a fully stocked tool box at work but basic hand tools at home, so anytime I need anything more than basic I have to remember to bring it home, or run to town and buy whatever it is and keep the second at home

 

[matt167]

I got it to run. Needed points. After pulling the old ones it became obvious. They had more green corrosion than the Statue of Liberty.. I also verified power before I pulled it apart. That also showed a problem. The new ignition switch from Napa is shorting power to the ignition terminal all the time.. I’ve got another to pick up from advance auto tomorrow

Carburetor might also have a leaking issue but one thing at a time. I got the engine to run but I didn’t try to keep it running without a good way to shut it off… I was also able to verify the shift interrupt is working properly