Your explanation does not make any sense...old coil type would be kettering ignition whereas new type would almost certainly be cdi, not interchangable.
Coils in the kettering system would be fed with, not a signal, but battery positive with the neg going to the points/condensor.
You cannot...
Look in batteryuniversity website for details and reasons for certain charge/discharge on Lipo or Lion batteries.
I doubt the voltage would be increased.
There should be some form of internal regulator to stop you from "fast charging" anyhow as no apparent dedicated charger is used apart from a...
Don't start out as a "free energy" geek.
One good rule to remember, surprised you haven't learnt it yet, energy out is equal to energy in , minus losses.
The controller you'll have to make would be many times larger than the motor.
No good thinking along your current lines as it would all be encased within a microcontroller with little chance of "tapping in".
Simplist and smallest would be the small dc vibrator motors out of phones or tail rotor...
Yes, all seems a waste of time to me.
These things are as cheap as chips and, in most instances, those with a C tick at least, conform to safety regs.
Amateurs modding things and then stringing them up in public are just asking for trouble.
You obviously have an internet connection so do some Googling and some study.
Plenty of videos around on almost any subject you can think of.
Not difficult to separate the BS sites with genuine.
Simple solution...add a switch.......direct to battery supply.
If you've tapped into the ignition switch wiring, the permanent live cannot be too far away.
Think you'll find the output of the supply is a basic h-bridge and one polarity will give one output set/colour while the other (reverse if you like) gives the other.
As an exercise probably ok but I don't see the point in the whole arrangement.
A lot of gear that is unnecessary to make a relay activate.
Don't like the bias arrangement on the opto outputs either.
10k for the LED and 220k for the ldr seems extreme..............
Other than that, use 9v smoke alarm batteries might work in this instance but it will catch you out in the future.
Use a decent set of AA batteries.
If it's as thick as you "don't say" you will have difficulty soldering. Better to crimp.
Note:-(wire is measured in a variety of ways to convey the thickness...thick wire is not one)
We have no idea what you have there otherwise.
Just because a cable is a certain guage, doen't mean it was done...
Arduino will do what you want and much more..........just break each section down into working examples and then combine.
Just watch your approach to negative logic and fail safe as it will catch you out.(reeds)
different model...... you show MAS830L.......link shows M830B...so just use it as a guide, not "as a matter of fact"
Either that or break into the piggy bank and get a new meter....must be all of $30.