Plan to make alternator light for my scrambler project. I searched around forum but im still very confused. Im going to use 100kOhm resistor(0.5W) and Led light in SERIAL between alternator and battery. 
Is this going to work? Feels too simple and easy .  Any advice is highly appreciated

You will save yourself so much hassle if you just use an incandescent standard light in the charging circuit. If you use an LED and have to fit a resistor then you are gaining nothing as it will use the same amount of power and generator the same amount of heat.
All the other lights can be changed for LED without any problems.

Your idea could work but there are problems that LEDs create in this application. First off, 100K is way too big a value. You'll not see your LED light up at all since most of the potential will drop across the resistor. Choose 220 - 470 Ohm, 1/2W, 5%. The forward voltage drop on the LED will hinder the excitation voltage that gets applied to the stator of the alternator. In short, you'll have to rev the engine past 2500 RPM to get the alternator to start working and extinguish the LED. As suggested, using a regular 12V incandescent bulb will not present these problems. The indicator is rarely used and when you want it to work (i.e. show a failing alternator), the bulb will work well, the LED not so well. Save use of LEDs for markers and indicators, and trust a good old fashion bulb to this job.

Thanks!
Looks like i need to study electronics a lot more. Just so much other interesting things to do with this project. 
Ill use smallest(physical) possible incandescent light.