1967 Johnson 33 hp Starter Solonoid power

Joined
Aug 17, 2015
Messages
16
I am restoring a 1953 Thompson Thomboy, the power for which is to be a 1967 Johnson 33 hp. My problem is the starter motor will not crank unless I jump a wire inside the junction box from the Negative terminals to the left small terminal on the starter solonoid. As I understand it, that negative feed should be coming from the white wire "safety switch" up on the motor, which is tied into the vacuum. This is all new to me. I did verify there is continuity from the safety switch to the small terminal on the solonoid - - why won't this power the starter motor without a direct jump from the negative to the solonoid? Are there any problems running the motor with this jump wire in the junction box? I'd much rather know the actual problem and fix it.
An help is most welcome!
Thank you.
 

RCO

Petty Officer 1st Class
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Jun 15, 2016
Messages
350
Not a problem to source the ground from another source. I don't have the wiring diagram in front of me, but I don't believe your solenoid ground should come from the cutout switch terminal. The cutout switch only provides ground in an excessive vacuum situation to kill one set of points, the other wire should go to one of the M terminals at the ignition switch.
 

F_R

Supreme Mariner
Joined
Jul 7, 2006
Messages
28,195
Look at it this way. When you turn the key to start, power comes from the key switch, goes to one of the small terminals on the start solenoid. Then THRU the solenoid's winding and out the other small terminal. From the second small terminal it goes to a tie point at the corner of the vacuum switch (NOT through the vacuum switch). From there it goes to the safety switch, which provides a ground only at slow throttle settings.

If all that is as it should be, current flows through the circuit only with the throttle at slow. The flowing current is what energizes the solenoid, it clicks, and the motor cranks.

Now, by grounding that solenoid terminal, you are doing what the safety switch is supposed to be doing.

Bottom line: There is a fault somewhere between the solenoid and safety switch. Wire broken or disconnected, safety switch not closed, or safety switch burned up. Note: the safety switch will instantly be fried if somebody applies a direct 12V to it (not through the starter solenoid)
 
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F_R

Supreme Mariner
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Joined
Aug 17, 2015
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Thank you both! F R, the wiring diagram is most helpful and will be retained. I recently acquired this motor, with very little knowledge of its history.I have another restoration project wrapping up ahead of this one (1956 Yellow Jacket w/ 1965 Johnson 40 hp), but then we will tear into the 33 hp for the Thomboy - new water pump impeller, tune up, carb rebuild, and turning this long shaft motor into a short shaft.
This iboat forum is great, and I thank you for sharing your expertise so willingly.
 
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