Two Questions: Shift Cutout Switch and Coil+ in the Starter Circuit

[San_Diego_SeaRay]

Engine: 1981 Merc 260R MCM 350 (Rebuild project; hasn't actually been in the water yet)

Two questions if you could help:

1. I hook up my Ohm meter probes to the Coil+ and then ground. I get 7 ohms. Then I push down on the shift plate mechanism to complete the cutout circuit and I get 0.1 ohms. On my other engine (there are twins), I get Infinite ohms, then push the shifter to get 0.1 ohms. Shouldn't the 7 ohms be Infinite ohms as well? Is my coil grounding out thru the Distro? Or is my cutout switch bad? Or is this completely normal?
2. I bought a harness (canon plug) for one of my engines. It was explained to me that w. this harness I'd need to run a wire from the "S" terminal on my starter up to the B+ on my coil. Question is, how did Mercruiser power the coil at startup with this harness design?

 

[Bt Doctur]

Im assuming you have points ,you cannot test a coil unless it is completely disconnected. You might have a newer harness that used a T-Bolt IV or V
and didn't use that feature with electronic ign systems. how many wire do you have at the starter?
the shift interrupter is wired one side to the neg side of the coil and one side to ground

 

[San_Diego_SeaRay]

Im assuming you have points ,you cannot test a coil unless it is completely disconnected. You might have a newer harness that used a T-Bolt IV or V
and didn't use that feature with electronic ign systems. how many wire do you have at the starter?
the shift interrupter is wired one side to the neg side of the coil and one side to ground

• I have a Mallory Distro, originally points but upgraded to a Pertronix electronic
• I'm not actually checking the coil. I'm checking the shift interrupter.
• At the starter, I have the Orange Alternator wire (w. 90 Amp fuse) and the Red Circuit Breaker wire at the main post, and the Red/Yellow starter relay wire at the solenoid.
• My setup seems to put the shift interrupter wire on the + side of the coil

The problem arose when I predicted that the shift interrupter circuit should not have continuity from the coil to ground when not 'engaged'. But instead, I found it had 7 ohms.

 

[Bt Doctur]

no it does not, the ign is grounded thru the neg side of the coil. if you have the old style switch, it provided a ground to cause the engine to miss/stumble/stall to come out of gear.
If you have the new style plate , it interrupts the power going to the + side of the coil to cause the stumble/miss to come out of gear. a slight wiring modification is necessary.

 

[San_Diego_SeaRay]

no it does not, the ign is grounded thru the neg side of the coil. if you have the old style switch, it provided a ground to cause the engine to miss/stumble/stall to come out of gear.
If you have the new style plate , it interrupts the power going to the + side of the coil to cause the stumble/miss to come out of gear. a slight wiring modification is necessary.

On one of my engines (the subject engine), somebody merged the purple and green/white (cutout switch) wire w. a butt connector and then wired that junction to the B+ on the coil. So maybe they took the old style (coil -) and made the new style (coil +). I plan on doing the same w. my other (twin) engine. I don't think it will hurt anything (hopefully).

About my original question, it seems to me that having Ohms present thru the shift interrupter (when not shifting) is a potential shunt to ground for the purple wire. It *could* at times become the path of least resistance, essentially bypassing the coil all together. Simply put, it seems like that circuit should be completely open when not shifting and completely closed during shifting.

 

[Bt Doctur]

is your switch the roller type or the plunger type

 

[San_Diego_SeaRay]

I'm going to say roller type because it has a metal prong that has a little roller at the end of it. Looks like this:

 

[Bt Doctur]

that is a normally open and closes the contacts when activated. made to supply a ground to the neg side of the coil.
From what I understand about that electronic system it has 2 wires from the module and connects to the pos and neg of the coil. the system uses full 12v to power it, not supposed to have resistance wire.

 

[Bt Doctur]

 

[Bondo]

On one of my engines (the subject engine), somebody merged the purple and green/white (cutout switch) wire w. a butt connector and then wired that junction to the B+ on the coil. So maybe they took the old style (coil -) and made the new style (coil +). I plan on doing the same w. my other (twin) engine. I don't think it will hurt anything (hopefully).

Ayuh,.... They did it wrong,.... Listen to BD, 'n do it Right,....