"The switch you describe is no
"The switch you describe is not a thermo switch for the warning horn. It is a automatic switch for the dual action electric choke, a goof on OMC' part. It sounds like it has been converted as per OMC's instructions so that the choke works positive only when one wants it to operate (as follows).
(Temperature Actuated Choke Solenoid Conversion)
(J. Reeves)
Various OMC engines that were manufactured in the later 1960s thru the early 1970s, for example the 1969 55hp Evinrude/Johnson incorporated a dual stage choke solenoid...... easy to identify as they have two wires leading to the solenoid, one purple/white, one purple/yellow.
The purple/yellow is attached at the engine wiring terminal strip to another purple/yellow wire that led to a heat sensor. The initial stage, with the key ON, (purple/yellow), when cold, would keep the choke pulled in half way until the engine warmed up, at which time it would release and open the choke butterfly.
The second stage (purple/white) is attached to another purple/white wire at the engine terminal strip which leads to the choke switch. When the switch was engaged, the choke closed etc.
The problem with this setup is that as the engine got older, the thermostat acted up, water pump became weak, whatever, the heat sensor failed to operate properly and the choke would not release from that half closed position. This would cause the engine to run in a rich fuel mixture condition (flooding, loading up).
The cure to this problem, via a service bulletin from OMC was to remove the solenoid purple/yellow wire from its original location and connect both of the solenoid wires (purple/yellow & purple/white) to the engine wiring harness purple/white wire at the engine terminal strip.
The above change would allow both solenoid wires to be energized when the choke switch is engaged, pulling the choke butterfly in firmly..... and only when the choke switch is engaged.
When time permits, visit my store at:
http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store
To test the warning horn (engine not running), key in ON position, find the TAN wire that is protruding out of the cylinder head, slide the insulating sleeve back and ground that connection. The horn should sound. If it does not, find out why as that's the only warning you'll receive if the engine starts to overheat.
On that model, you'll have a PURPLE wire from the "A" terminal of the ignition switch to one of the horn terminals, then a TAN wire from the other terminal to the heat sensor at the cylinder head.
Head bolts should be torqued to 18 to 20 foot pounds in the following sequence:
9...10
5....6
1....2
4....3
8....7"
