This is all good discussion, but it doesn't answer my original question. Why have I never seen one of these installed on a car? This was missing on every AMC I've owned (only four I'll admit). Did people routinely remove these? Todd On Monday 13 December 2004 18:59, david crooks wrote: > >You can run one of these Motorola alternators > >without the isolation diode but it is like > >replacing a fuse with a slug. > > True, but I'll return to this in a second... > > >The diode ... is there to protect the internal > >diodes which are much harder to replace. Clip > >your jumper cables on backwards and the isolation > >diode may go, but the circuit to the internal > >diodes should then be open and protected. > > Sorry but this is completely wrong. > The isolation diode will provide no protection > against reversed jumper cables, it allows current > to flow in the same direction as the rectification > diode pack. It's purely the luck of the draw as > to which diodes blow first, and the smaller diodes > in the rectifier pack are more likely to go first. > > The isolation diodes purpose is to remove the alternator > and regulator from the electrical circuit when the > alternator generating any voltage. This used to be > done with a cutout relay, but the diode solution is > simpler and much more robust. Your alternator will > work fine without it, but you'll see two side affects. > First your charging voltage will by about 0.7 volts > higher, which is what would normally be lost across > the diode. Secondly it eliminates battery charge > leakage through the alternator when it's not running. > In other words remove it, and you'll find your battery > going flat more often... > > Cheers, > > Dave