On Fri, 28 Mar 2014 17:25:50 -0700 (PDT), Tim
wrote:

What I'd recommend is that if you have a 55a alternator, I'd go with an isolator capable of
at least a 70a. load. A 70a. alt- 100a. load etc. . Always go at least a step higher amp isolator
than what your alternator is rated for.

I have a 120a. alternator on my '77 Marquis, and I use a 150a. isolator.

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What is the forward voltage drop across the diodes in the isolator?
That was always an issue with some of the older isolators unless you
had downstream voltage sensing for the alternator.