The smaller items such as fuel sender and water gauge (If electric) only require small droppers. The heater circuits though draw high loads, so a large dropper is required. This causes lots of heat, so a good heat sink is also required.
Dont forget you need a 12v coil, as well as light bulbs inside and out.
The 6v starter is ok, it just spins faster which most people find is a bonus!
I have stayed on 6v with my car. You can get a 6v alternator, 6v halogen lights, 6v electronic ignitionand coil, and for those important items you can buy a 6v to 12v Voltage Booster to power up a cd/radio or cigarette lighter to power your sat nav/ mobile phone. I think this is a better option personally.
I have 'borrowed' the following from a post on the other channel
For small stuff, you can use a resistor in the circuit. A heater motor would be OK for this method if it's not really powerful.
Unlike using an electronic voltage dropping device, which will power a number of devices; you'll need to fit a voltage dropping resistor to each circuit individually.
To work out what resister you need, you have to know the current the device uses and the voltage you want to drop. So, for 6v device using 1 amp, you need to drop 6v on a 12v system.
Voltage to drop
______________ = Resistance you need in series with your device
6 volts to drop
_____________ = 6 ohm resistor needed
1 amp for the device
You need to work out the power rating for the resistor: DC Watts = Volts x Current
So in this example you'd need a 6W resistor - The power is calculated from the 6v that you have across the resistor x the 1 amp current in the circuit
Using resistors works well for small devices that use a constant current, but if you're dropping the voltage for a 10A device, you need a resistor rated at 60W power, that's quite a bit of heat to get rid of and the resistor will need a heat sink fitted.
Also if the current isn't constant, e.g. a fuel guage circuit, you'll only get a correct reading at empty or full on the guage according to whether you drop the voltage against the "empty" or "full" current.
RS components are a good supplier for power resistors and heat sinks.
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