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Obsolete temperature switch, what are the options?

Northern River said:
Thanks Joe for educating me, this is certainly a good option. I will look up the fast start feature just for my knowledge. You have been helpful in the past and you are helping me again, faster than the dealers that I have asked for advice.
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What wires go where from the starboard sensor to the port side wire what wire to wire nut together with the starboard temp sensor
 
Is this still relevant? I am working on a solution for 2005 115 Johnson; open to posting progress and ideas for review, criticism, ridicule and other uses here if there is enough interest.
 
Nah, I don't have an immediate problem; mostly interested in designing it out of a sporting interest, and in case somebody else might find it useful. Thanks for the tip, though.
 
OK, so I looked at the schematic again (2005 115 PLSOR). The switch seems to be 2-in-1, with B/W (warm-up) wire running to the ECM, and Tan (overheat) wire running to the starboard switch and forward to the dashboard. Both switches seem to connect their respective wires to the ground when closed. So I thought I'd poke around.

Voltages to ground (V):
B/W Tan
Ignition off 0 0
Ignition on 0 4.26
Engine running 10+/- 10+/-

Current when connected to ground, engine running:
B/W 10 mA; Tan 20 mA, overheat buzzer activates.

I have a rough idea for a solid-state replacement for the switch, but I'll need 12V and ground. Any idea where I can access good clean voltage?

Anybody knows what is the thread size for the plastic plug that holds the switch in? Measured to about 9/16th, and looks pretty coarse.

(In case anyone wonders, the motor behaved normally on a fishing trip the next day, so I assume I did not fry anything)
 
joereeves said:
Well, without giving it a lot of thought and just running the circuitry through my head a couple times... this is the first I've heard about a diode but if it exists, it would be to prevent a interference between the two heat actuated contacts within one unit I'm thinking... BUT... changing to a single wire heat sensor eliminates that conflict and reverts the system to a proven circuit (overheat only) that has existed for years.

Personally I don't know for sure if that Black/White wire eliminates the "Fast Start" feature simply by grounding it out or not... BUT... if it does, and the grounding out is performed by that switch within that is coupled with the port overheat sensor... then the grounded circuit is the same all the time the engine is running whether it's grounded directly from the powerpack black/white wire to ground or via that expensive, over-priced non available two wire barrel.

If my two above paragraphs hold true... I can only wonder what solution to your problem was going thru that technicians mind.
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If my above thoughts are in error, I'd appreciate having other members with the advanced knowledge to jump in here to set me straight as I'm in a sort of borderline knowledge area here due to retiring in 1991... and a ohm test I did on a few of those two wire barrel units as follows:

Having two or three of the 2 wire (Fast Start/Overheat) sensors (new) a number of years back on my bench, I seem to remember..... When checking it out that the Tan wire with a ohm meter, the heat sensor circuit was "open" normally, "closing" only if overheated (No problem)... BUT........

When checking the Black/White wire with a ohm meter, that Fast Start circuit was closed (cold). <-- That sticks in my mind. I didn't reverse the meter leads as I wasn't aware of a possible diode being in that circuit, never gave it a thought. I sold out of them so there's no way I can redo the test. Those overpriced things never came back so they must have been okay.

Unfortunately I can't remember if both units engaged via a certain temperature by grounding out... or one grounded out, and the other becoming open.
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when the temp is above the sensor parameters (140, 160180 degrees just a example) the temp side closes to ground and that makes the black-white wire put the engine in slow mode because it is over heating. engine in slow mode will not run past 2500 rpm due to the power pack restricts the engine power to 2500 rpm or lower so not to damage the engine. YES there is a diode in the engine harness that only lets power go in one direction, it is under the harness tape nearest the harness connector. it will have a heat shrink about 2 inches long. the sell them as a diode kit about $40. If it is bad it will also put engine in slow mode.
 
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