Lightupyrday

I know this is a late comment, but I just looked here for some info on my Lexus. I'm a retired electronic engineer in medical x-ray, CT etc. and deal with both high voltage and low voltage/high current circuits. I wonder if that quote of 5 ohms should have been <0.5 ohms, as at 12 volts, 5 ohms is a huge amount of resistance and a starter motor would not turn over. Even headlights would draw enough current to severely drop the voltage. The main battery leads + and - are heavy (25mm2 Copper) to reduce resistance. I look for around 0.01 ohm max to the chassis or starter motor. Two headlamps at 65W (130w) will draw 10.88 Amps at 12V ( 130/12 = 10.88A) The resistance of the two headlamps is calculated by R = E ÷ I (E =Volts, I = Amps) Therefore 12v / 10.88 = 1.1 ohm. Therefore even a 1 ohm resistance in the wiring will halve the voltage at the headlights and a 5 ohm resistance will hardly make them glow. The lower the voltage the more important resistance is. This is why AC mains is supplied for great distances at very high voltages- Here in New Zealand we use 230V which can operate with less copper in the wires than in USA at 120V A starter motor may draw say 100Amps (100 x 12 volts = 1200 Watts) and the starter motor will have a resistance of 0.12 ohms. Thus even 0.1 ohm resistance in the wires will approximately halve the voltage and may not allow the starter to turn over. Meanwhile a lot of heat is being generated in the starter leads. I have found there is much confusion in understanding the relationships between Resistance; Watts; Amps and Voltage even in auto and domestic electrical trades. Once you get your head around it, it becomes basic nature. I learned this analogy at College in the 60's - "A Volt chased an Amp thru an Ohm" Likewise, 10 volts will chase 10 Amps thru 1 ohm; and,,, 10 volts will chase 1 Amp through 10 Ohms. The formulas are available online.