mercury 500 50hp ignition connection

[sambrigman]

ignition wire completely gone.so i have replaced the wire, but cannot find where it connects on the motor. please help thanks i think it is around 1978 model

 

[Chris1956]

You might find an wiring diagram for that motor. iBoats has some on this site. Maxrules site also has some.

Normally the ignition wire would be grounded to kill the spark, and ungrounded to allow the motor to run.

What is the rest of the engine wiring harness look like? usually they are bad by now, if not replaced.

 

[sambrigman]

yes i have had a time replacing wires, this ign wire is the last hurdle, I have spent hours looking at wire diagrams.cant make heads or tails of these 1970s diagrams.I think that surely there is a common connection for all these old motors. Thanks

 

[Chris1956]

When you say ignition wire, which one(s) do you mean. On an ADI ignition like you probably have, there are wires from the stator to the switchbox to charge it. There are wires from the trigger to the switchbox to fire it and there are wires from the switchbox to the coils, to fire the coils.

There is also a single ignition killer wire from the ignition key to the switchbox. This is grounded to kill spark. They are pretty simple, after you work with them a bit.

 

[sambrigman]

the wire in question is connected to the i on the key switch when the key is switched on this wire is hot. The motor has no fire

 

[racerone]

If this motor has ADI ignition ( no distributor / 4 coils ) then 12 volts is not needed for spark on the plugs I believe.