1980-1981 70 HP ignition problem

[hammbone_merc70]

I've been troubled by this engine for some time now. had the ignition tested and replaced the switch box and stator. The motor would not start. So I read some threads on iboats and tried something I read about disconnecting the yellow/black wire from the micro switch, still the engine did not start. Next I disconnected the yellow/black wire from the switch box and behold the engine fired right up. What does this mean? Faulty micro switch? Also when i went to turn the engine off with the key it kept running, is this normal when the yellow/black wire is diconnected? Any input is greatly appreciated.

 

[ajgraz]

Re: 1980-1981 70 HP ignition problem

Yes, the yellow/black wire is the kill circuit. If it gets grounded, whether through tilting up the motor (the microswitch is a mercury switch) or key off, the switchbox power drains away and the ignition ceases.

Sounds to me like the wire is grounding out somewhere, either some insulation is gone, or there is a short somewhere like in the harness connectors or the ignition switch itself. Should be able to diagnose that with an ohmmeter.

You can run w/o the kill circuit wire hooked up at the switchbox, but you will have no protection if the leg kicks up (say, from hitting submerged object or a reverse lock failure), and you'll have to stop the motor with the choke button.

 

[hammbone_merc70]

Re: 1980-1981 70 HP ignition problem

Thanks it's got me fairly stumped. I'll look for a short or bare wire. hopefully I can find it by the weekend. I'd like to go fishing, but i'd like the motor to be working properly first.

 

[ajgraz]

Re: 1980-1981 70 HP ignition problem

I wouldn't let that stop me from a fishing trip if all else is OK. I ran with my kill circuit disconnected for a couple months until I finally broke down and rebuilt my entire engine harness. In my case the kill wire was creating an intermittent short inside the connector. It was maddening because it only happened if I bent/wiggled the cable at the connector in a certain way.

If you don't have it, here's your diagram:

I'd start with the engine harness, it's much more likely to be corroded or damaged. Second suspect would be ignition switch.