Mfi rpm transducer switch

[47silver]

Bench tested 2 repaiired mfi speed switches We used with a breadboard signal (hz) generator,
Results
Starting at 45 hz (900 rpm) we raised signsl with a pot. At 70 hz (1400 rpm) the relay in the speed switch energized and lit a pilot light.
Increasing output to 105 hz (2100 rpm) the relay de-energized and the light went out.
On lowering hz below 105 the light turned on and stayed on until we were about 70 hz (1400 rpm).
My original thought was relay was always on above 1500 but surprisingly to me the relay is off-on-off on increasing rpm and on then off on
My son built the signal generator

[356RS]

Great idea. Would like to see the wiring schematics.

[47silver]

tested the second one
at 70 hz the pilot light lit.
at 110 hz the pilot light shut off
at 109 the light lit.
at 65 hz ~1300 rpm the light shut off.

This one i think works best as it has a differential. 70 to 65 hz = 1500 and 1300 rpm.

we only replaced parts did not tune the resistor with 5k and 10k ohm pots that others have done so for #1 we need to try that so we can get a better differential. Specs call for 70hz on at the low end and 65 off. I never found a spec at the high end but both transducers are around 110 hz or 2200 rpm when they shut off and about 2150 when the turn back on.

I'll post some information on the breadboard circuit etc when I get a chance.

I think when testing these in the car, you should keep the rpm between 1700 and 1900 and then press the micro-switch. i had the #2 switch in the car and was above 2100 rpm when testing and did not think that it worked.

[Wasatch 911S]

Here is the schematic.

[47silver]

These are some quick photos of setup

[47silver]

Additional photos
pics

[47silver]

Sorry about the orientation

[47silver]

This one Above 110 light is out

[47silver]

Warren's diagram shows
K1 on above 1500
K1 off below 1300

We are finding that K1 goes off again above 2200. ~110 HZ

Can anyone verify that this correct?

that would mean
K1 off below 1300
K1 on between 1500 and 2200
K1 off again at 2200 or above,

We replaced the transistors and used D1 on 2 boards and they work the same so i am wondering if we are correct or is something wrong with our boards?
to meet it makes sense to be off again above 2200.