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Old 02-10-2011, 08:37 AM   #13 (permalink)
Ptero
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Join Date: Oct 2008
Location: California
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I wouldn't change the alternator. First thing I'd do is replace the battery with an Optima D27F. It's 3/4" longer and 1 3/4" taller and a little narrower. It has 1025 cranking amps @32F vs the 650 CA of your OEM battery. It is 22 pounds heavier.

Next, wire the light circuit directly to the battery. Since the alternator doesn't pull a load until the battery voltage falls to a low voltage trigger point, you will be able to drive for quite a while (probably hours) before the alternator kicks in. In typical situations, especially in a diesel which does not use spark, the alternator may not kick in at all and you will be able to use a battery charger at your destination. AGMs charge faster than standard lead acid.

Never use resistors. Wire lights in series to match 12v.
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