1999 Dodge Ram RPM Signal

Hello all! I’m working on a little project using an arduino to remote start a vehicle and I’m looking for an rpm signal I can work with. I see the what people use for traditional systems is the black / grey wire on the ignition coil. I have no oscillascope to see what the waveform is. Ideally I would like a 5vdc pwm. Any advice would be appreciated. Thanks in advance. Mike

Did you try the black/grey wire?

https://api.motor.com/v1/Information/Vehicles/Attributes/BaseVehicleID/1902/Content/Documents/Of/WiringDiagrams/7714332?Scheme=Shared&XDate=1556668326&ApiKey=YWWodJ8Irm&Sig=UAVXJqvsf2SDEUKnGfoIzCsNt1fcOHre35PpV6iLbUM%3D

Yeah I checked that wire. I can’t tell what the signal is but the voltage is too high. I think I’m going to check the crank sensor wire. That wire should go to the PCM module on the passenger side fire wall.

Sorry ween I can’t open that link for some reason.

Oh well....PCM connector C! pin 8 maybe? gray/black ..Crankshaft Position Sensor Signal

How much too high is the voltage? A simple 2 resistor voltage divider will work. http://www.ohmslawcalculator.com/voltage-divider-calculator

I thought of this as well however I have no idea what the signal is to design this voltage divider. I measure on AC an get +20V when revved and when on DC 4V? Seems weird so I am trying to stay away from this wire. The PWM signal I can get from the crank sensor I think is best. Hopefully I can try this out tomorrow. Next is door locks and starting! Again, thank you both for your input!

Just out of curiosity is there anything else I could use as a "run" signal that would be better or easier than the crank sensor? I don't really need an exact RPM. Just looking for something to say hey I'm running don't try to start again.

Another question. Does anyone know the minimum voltage for crank sensors that produce an AC output signal? I know the magnitude will increase with RPM but what is the minimum at idle?