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'1974 mercury 20 hp won't key start

kyle_m

New member
1974 mercury 200 20HP SN:3756543.

I have just rebuilt the power head on this motor, everything runs great except that it wont start with the key. It seems (to me) to turn over enough to start but just wont fire up. It will however easily pull start. I also am not sure when the last time it did start with the key.

Battery has good full charge
Has spark to the plugs with key start
have checked all the wiring per the wiring digram to be correct

thanks in advance to anyone who can offer some advice.
 
Re: '74 mercury 20 hp won't key start

Ok, just to be clear.

When you pull start it and it fires, is the harness connected to the control/key or do you have to disconnect the engine harness to get her to fire?
 
Re: '74 mercury 20 hp won't key start

thanks for the response. I have only been able to get it to start with the harness disconnected from the motor.
 
Re: '74 mercury 20 hp won't key start

Ah-hah! Your harness is grounding out the ignition somehow.

Try this: Disconnect the harness, then jump the solenoid directly frpm the battery with jumper cables. (And don't mix up the polarity!) It should fire right up that way.

Jeff
 
Re: '74 mercury 20 hp won't key start

thanks jeff.

could you give me a little more detailed description of how to jumper the solenoid? There is a red (+) wire, black(-) wire and then a yellow (?) wire going to the solenoid. Not sure what to do with the yellow wire.

kyle
 

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