81 Mercury ignition problem.

[AceyDeucey]

Hi guys, I'm new at this - boats, outboards and forums. So please bear with me if I don't use the correct terms etc..:redface:
I have a 1981 Merc 700 with thunderbolt ignition with 1 coil per cylinder.
I have been having an occasional odd problem recently where the motor had no power under acceleration and the more throttle I gave it the more it sounded like it was going to choke, but back it off into neutral and wait a while and it would run great. This only happened occasionally but I thought it might be worth mentioning.
The reason that I'm posting now is, my motor just died 14km from shore. (Lucky I was with a mate and his boat and a tow rope). Now the motor turns over fine but will not fire up, I find I have no spark at all 3 spark plugs. If I remove the orange wire from my switchbox (the one connected to the safety switch) the motor fires up and runs fine. Is this kill switch faulty and just needs replacing or is this switch doing its job and stopping the motor from running because there is another problem?
If anyone has any thoughts they would be appreciated.
Cheers.

 

[Chris1956]

Re: 81 Mercury ignition problem.

The orange wire is grounded to kill the ignition, by the ign switch or the emergancy kill switch, or perhaps the mercury switch that detects over tilt of the motor. It is usually mounted on the front cowl support and s plue.

There is not other function tied to the orange wire. In your case, I would think the kill switch is bad.

 

[AceyDeucey]

Re: 81 Mercury ignition problem.

Thanks Chris for your reply. Looks like it is not my mercury switch is functioning fine after all. I think the problem is the orange wires are going to earth somewhere. Am I right in thinking that if all conditions are fine the connection between the orange wire and earth is broken, thus telling the switchbox to allow spark?
The mercury safety switch is working fine, the neutral safety switch is working fine, the orange wire right along the harness is in good condition with no breaks in the insulation, but the orange wires to the switchbox and the mercury switch are constantly showing continuity to earth. They are doing this regardless if the ignition key is in either the on or off position. Should turning the key also break the connection to earth?
Please help guys I've nearly got no hair left to pull out.

 

[CharlieB]

Re: 81 Mercury ignition problem.

Unplug the main wiring harness from the motor harness and retest the orange wire to ground again on the motor side, if the wire is now un-earthed then the problem is within the main boat wiring harness/switches. If the orange is still grounded then disconnect the tilt switch and retest again.

 

[AceyDeucey]

Re: 81 Mercury ignition problem.

Thanks Charlie. The orange is still grounded. Tilt switch is disconnected. Problem is within motor wiring somewhere. I can't get to the back of the harness plug to check there. Is there any other way the orange wire could be grounding?

 

[Chris1956]

Re: 81 Mercury ignition problem.

The harness plug is removeable. Two screws and a clamp.

Alternatively, disconnect orange wire from powerpack and mercury switch and test with ohmmeter. If still short it is lokely the motor harness is shorted to ground.

 

[AceyDeucey]

Re: 81 Mercury ignition problem.

yeah I've removed the harness plug from the motor but the plug is sealed and I'm wondering if the problem is inside it. The Orange wire is disconnected from all connections. Tonight after work I am going to totally remove the harness off the motor. I must find the problem then I'd think...

 

[AceyDeucey]

Re: 81 Mercury ignition problem.

Just to finalise this thread.
Problems was found - there was a short in the harness plug on the motor side. Kill wire was shorted to the choke earth. I cut the loom and bypassed the plug for the choke wire . Motor starts no worries now. When I find a new harness I will replace the lot.
Many thanks to those who offered their advice.