I guess that's why in another thread someone had mentioned putting in a rectifier bridge to make it DC current. I thought that was optional, maybe it isn't.
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Nope, not optional if using a turn signal flasher, or LED, or charging a battery.
As I said on the other thread, you're pulling too much off the flasher anyway, so you need a battery.
Your standard incandescent lamps will work fine, AC or DC. (Until they blow at high RPM without a battery)
It's AC and DC "Voltage" not current. That's sematics right now, but when you start configuring voltage, load and current draw, it is salient.
If you get a battery, a rectifier and charge it, most of your lighting challenges go away. That's why production vehicles are done that way after all. :shrug:
A basic snapshot of AC to DC via rectifier: AC means positive, then negative voltage, up and down, through zero, and everything. The speed of this positive to negative oscillation (ever heard of an oscilloscope?) is what is called "frequency."
What a rectifier does in this case, is to chop off the bottom end of the AC voltage giving you something called pulsating DC- This type of pulse still oscillates at what ever frequency it's at, but most basic DC components (light bulbs or simple motors) don't care.
What a rectifier regulator does is takes this pulsating DC and makes a high and a low value and ensures only that value is allowed to continue on in your circuit. To charge your battery. Since portions of that aspect are sensitive, running them straight to heavy loads can fry the components in that system. Consider your battery an electrical shock absorber.
You can find this on the net, but it's pretty important to understand these basics if you're trying to engineer an electrical system.