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Old 10-16-2020, 02:10 PM   #1
Junior Member
Newmar Owners Club
Spartan Chassis
Join Date: Nov 2016
Location: Wausau, WI
Posts: 21
400 ISL alternator and dead batteries

So the saga started with a dead pair of chassis batteries. Limped in to local shop and determined the alternator was bad. Now new alternator but chassis batteries drain very rapidly (actually one battery cable has 3 amp draw when isolated, the other only 0.3 amps). Traced proble so fR to a small gauge jumper wires that goes to a 3 bolt bus near the alternator on lug “L”. No idea where the wire goes after that into the harness and the frame.
With the jumper wire off no draw and no check engine lights. The shop who replaced the alternator weeks ago is not sure anymore if the old alternator had the same wiring configuration. They suggest just disconnecting it and taping it off and see if anything stops working. Not my idea of a good time heading to Florida. They don't think a small wire of this gauge would carry anything major, but ????.
Spartan send them the requested wiring diagram: it showed two batteries with a positive and negative lead with the negative attached to ground. No more than that. Obviously not only not helpful, but insulting.
No idea what to do next.
2004 MADP
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Old Yesterday, 09:00 AM   #2
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Many times what a coach builder designs is not quite what you get when you drive it off the lot. As "stuff" is added, and it may be a newer modification of a system already present on the original design, additional needs for power need to be filled, so... another source is found, anywhere. Many times this is the reason for people claiming they shut off all coach power and then found dead batteries. Someone put a power tap at the first convenient post.

Depending on how accessible your mystery draw wire is at the alternator, I'd disconnect it for your trip and see if something obviously shows up. If that lead is hard to access, I'd extend that wire in a large loop so the loop is easy to get to. Then if you cut and tape the ends and you later find it powered something you need, a simple splice will but things back on line. You can always clean up the added spaghetti when you get to your destination or even back home. Remember too, the wire loom installed originally on your coach may also be used on other models and even if that lead was sitting there unconnected for a reason, used on a different model(?), some helpful soul may have connected it just because it was there.
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Old Yesterday, 09:59 AM   #3
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Location: Clovis, CA, USA
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"They suggest just disconnecting it and taping it off and see if anything stops working."

I think that's a good idea. At least for an hour or so to see what quits working.

3 amps is a pretty hefty draw.
2004 Monaco La Palma 36DBD, W22, 8.1, 7.1 MPG
2000 LEXUS RX300 FWD 22MPG 4020 LBS

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alternator, batteries

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