72? 100 HP Johnson won?t start

GLE3

Cadet
Joined
May 5, 2010
Messages
27
Got issues with my outboard, and the wounds may be self inflicted. Tried to do the repair below but never successfully got 12V to the powerpack. Instead I have a motor that won't crank(It was starting before the repair). My battery is in good shape and I can get 12V testing that.

Work I was doing when it happened (My voltage was weak to the powerpack):
(Voltage Drop To Battery Capacitance Discharge)
( Pulsepack When Electric Starter Is Engaged)
(J. Reeves)

On the older Battery Capacitance Discharge ignition systems (1968-1972), the electric starter reaches a point, even with a top notch battery, whereas the starter will draw excess voltage/current/whatever which results in a voltage drop to the pulsepack. The cure is to purchase a diode which is capable of handling 12 volts and installing it between the starter terminal of the starter solenoid (NOT the battery cable terminal) and the wiring terminal that supplies voltage to the pulsepack.

The diode must be installed so that the current flows from the starter terminal of the solenoid to the pulsepack... NOT vice versa. When that diode is installed in this manner, when the key is turned to the start position, the voltage that is applied to the starter is also applied directly to the pulsepack via the diode effectively eliminating the voltage drop and energerizing the pulsepack with the required voltage needed for its proper operation.




Not sure if what I was doing caused this but now I don’t get any voltage past my solenoid. Hopefully I just blew a fuse or something. Would anyone know if there would be a fuse to check along the wiring harness? And where it would be approx?

Last question: My starter solenoid has 4 terminals. One goes to the starter, one goes to the battery, one goes to ground, and one goes to the key switch. Anyone have a guess on which of those terminals I should be connecting my wire too?

Any help would be appreciated! Thanks!
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 72? 100 HP Johnson won?t start

You may well have blown the fuse. The main wiring harness has a 20 amp fuse in it. It hides inside a rubber bulge on a wire close to the starter solenoid. It's a special, small 20 amp glass fuse. May not find one at the local auto parts store.... If you go out to the factory parts list website: epc.brp.com, you can see the parts list for your engine. That fuse is item #96 on the ignition system diagram.
 

GLE3

Cadet
Joined
May 5, 2010
Messages
27
Re: 72? 100 HP Johnson won?t start

Ok, found the fuse. Honestly don't know if it was blown or not because I broke it trying to twist it out of the bulge. The rubber was hiding the filament enough so I couldn't see most of it. Anyway, I need a new fuse. So your saying I'll have to get in touch with a marine dealer for this fuse? If an auto parts store carries a 20 amp glass fuse is that good enough?
 

Daviet

Fleet Admiral
Joined
Sep 24, 2008
Messages
8,958
Re: 72? 100 HP Johnson won?t start

You can put any 20 amp fuse into the holder to test it, but in order to seal up the holder you will need the proper lenth fuse. My local auto parts store did not stock the proper lenth fuse but they ordered in a box for me, had to buy all 5 fuses.
 

emdsapmgr

Supreme Mariner
Joined
Dec 9, 2005
Messages
11,551
Re: 72? 100 HP Johnson won?t start

The problem is that the factory fuse is much shorter than the typical auto fuse. Daviet offers a good solution if you don't have a dealer close by.
 
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