The V8 Owners Forum -

I still can't see why having the isolator in the + or - circuit of the battery would make a difference.

Isolating either end of the battery isolates that battery full stop.

What am I missing?


btw, even having a machine-sensed regulator in your alternator, if it is connected wrong, will still cause a current drain.

Is your battery remotely located?.

Update:

I found an isolator switch with a much higher peak current rating, so I can use it in line with the starter provided I don't switch it when cranking. This has stopped the current leak flattening the battery.

I have also found the current leak - it was the alternator. It has been replaced, and loads of weird little running issues with the car (like the noisy sensor readings, plus the most annoying one - slow cranking for the first 3 seconds of starting) have completely disappeared. It seems this problem was well worth solving!

The alternator output is permanently connected to the battery. It's the action of the rectifier diodes, which are like a one way valve, which prevents it drawing current with the engine stopped. The most common failure for a diode is to go short circuit. This doesn't stop the alternator charging, but cause it to draw current of a few amps from the battery when the engine isn't running. I can imagine it also producing a strange waveform instead of the normal series of positive going halves of a sine-wave, since the diode bridge removes the negative going ones from the original 3 phase AC signal. The battery will attempt to remove this negative going pulse - but how well it does that will depend on the wiring and other factors.