I was installing an amplifier in a car this weekend. From the negative terminal of the battery to the back had a resistance of 1-1.5 ohms which seemed high to me. Is this typical or should it be lower? Would this affect the amp at all?
Well our car has a battery at the back of the car. The negative is earthed to the bodyshell. There are two positive cables to the front of the car. The one that feeds the starter motor can be cut by an explosive bolt in the event of an accident, and the small one has a 200A fuse.
So BMW reckon that if the small wire is shorted to ground in an accident, there will be plenty of current to blow a 200A fuse. However the starter motor takes a lot more current, so much that a fuse can't be used. I guess that the starter motor current can hit 500 A, so the total resistance, including battery, starter motor, cable and bodyshell, is about 20 mΩ.
I also think that if bodyshell had any significant resistance, they wouldn't use it for earth. That means that the bodyshell is less than 1 mΩ.
If you are seeing 1 - 1.5 Ω ground resistance, you certainly won't be able to start the car. 8 - 12 A will not even make the starter motor click, let alone turn the engine. It would also make any fuse over 10 A completely redundant.
How did you measure the resistance? My meter shows about 0.4 Ω for just its own leads, and if I wanted to measure from the front to the back of the car I would need something to extend the leads and that something would have resistance.