Re: 1971 80 hp Merc outboard won't shut off
The ign system on your motor has to have power to make spark.
Check out the side of the switchbox opposite where the distributor wires connect.
You'll see a number of wires connected to the terminals, including 1 or 2 reds and a white.
The red wire is non-switched +12V power directly off the battery to the switchbox.
The white wire has no power with the key switch in the "OFF" position and is powered-up in "ON" and "START" positions to make sparks.
So, for some reason you're not dropping power to the white wire with the ign switch "OFF".
Most likely it's a bad switch. The other possiblility would be a short circuit in the wiring, either at the switch terminals or somewhere in the harness. The latter is a very unlikely problem; the switch being bad would be my bet.
You can test this circuit by disconnecting the white wire and measuring from the wire to engine ground with a voltmeter or test light. No power should be present on the white wire with the key switch in "OFF". This should confirm the diagnosis, then you can tear into the control box for a look at the switch and wiring.
You may have to unsolder or disconnect the white wire(s) from the switch to confirm a bad switch or other problem.
Here's a link to a wiring diag for your motor, it'll give you a better idea of what you've got:
http://www.maxrules.com/oldmercs/Wiring/1966ona/30.gif
HTH............ed
