Firstly 'Hello to All'
I've been tinkering with electronics for 50 years and am still alive to tell the tale although, in my youth, I did have some unfortunate contacts with anode voltages of Military wireless sets.
I will try to explain the problem - please tell me if I'm not making things clear.
I would like to use a Makita BLDC cordless drill motor and gearbox for some equipment we're making.
It offers a compact and reliable motor and gearbox which will require a housing made but that's not a problem.
The plan is to throw away everything else and drive the controller from a PLC and use an external power source.
The battery supply has a small third terminal which, I think, goes to a temperature sensor in the battery.
Connecting a 220

resistor to +ve makes the drill happy to run off a bench PSU (it is an 18 V drill).
Next, and this is where the fun starts, the trigger.
It is marked as an Omron C3JW-4B but (apart from buying replacements at 1/3 the price of the whole drill) there's nothing about it on the Internet - trust me !
Contacting Omron they tell me Makita bought out their division that makes similar switches and regard its workings as a proprietary secret so no datasheet.
The trigger has two components - a set of beefy contacts to supply +V to the controller and a 5 pin miniature connector.
There's a first pressure which switches power and a second pressure which starts the motor and makes it spin faster the more it's pressed.
There's also a forward/reverse (F/R) switch.
Nothing too difficult so far.
Disconnecting +ve in and +ve out from the switch and jumpering them together lets the motor start on second pressure and run as expected.
So, a 5 pin 'black box' to sort out.
I cut the wires and took them to a breadboard - the drill still worked !
With the controller connected there were three easy ones - GND which was common with I/P GND
One which sat at 18 V until second pressure then fell to 0 V no matter what so it was there to detect 'second pressure'
One which sat at 3.5 V with the F/R switch in 'Forward' and 0V with the switch in reverse.
Disconnecting these from the trigger and jumpering them to GND as required gave the expected results - motor starts on 'second pressure' in the direction set by the F/R switch.
This left 3 connections to the trigger - GND, grey and white (colour of wires).
With the controller connected to the trigger white sat at 2.5V no matter what and grey went from 2.2 to 0V as the trigger was pulled.
Easy !
White is the excitation voltage for the speed pot and grey is the 'wiper' O/P.
So, disconnect the trigger completely and look at resistance values with my trusty Fluke DVM.
I should say for all resistance measurements I took them with the DVM leads both ways round in case of a diode type junction somewhere.
The 'second pressure' detect went from O/C to 'closed' as expected, as did the F/R switch.
White to GND read a constant 15

while grey to GND went from 15 to 0

so that seemed to fit in with white supplying 2.5 V across the pot which was passed back to the controller by grey on the slider to give speed.
15

seems a bit low but anyway let's connect two 10

resistors between white (2.5 V) and GND so we should get 1.25 V at the junction and connecting that to grey should give half speed (or thereabouts).
Now this is where the mystery starts (hope you weren't holding your breath).
With the two resistors between white and GND white fell to 0V so it wasn't happy feeding 20

let alone 15.
I completely disconnected the trigger from the controller.
I put a 220

resistor in series with white
and the DVM read 15

between the free end of the resistor and GND.
I put a 220

resistor in series with grey
and the DVM read 15 to 0

between the free end of the resistor and GND.
In other words the DVM couldn't see the 220

resistor.
How is this possible ? The 220

resistor measured correctly.
I checked white to GND and grey to GND for volts (in case of a capacitor or backup battery) and diode (both ways) but nothing.
I repeat there was no voltage supply of any sort (apart from the DVM) to the trigger - it was literally in my hand.
HELP (Please).