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Old 10-15-2021, 02:15 PM   #1
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Join Date: Oct 2020
Posts: 480
28si alternator conversion - now no tach?

I'll do another thread about what went wrong..... This one is just for the current issue.

Here's how my old alt was wired.

I connected B+/B- to the new alternator in the specified places, connected the
KEY SWITCH wire to I and the DUVAC wire to S. The 4th wire I assume is the tach and I connected it to the R terminal.

Now I don't have a tach. I seem to be getting good voltage (14.4) even at idle and there are no ALT related dash lights. My BIRD is working and my battery monitor shows the battery is charging.... So I think things are wired correctly except for the tach. Any thoughts?
2000 Monaco Diplomat 38D
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Old 10-15-2021, 03:35 PM   #2
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Posts: 9,967
I assume the old alternator was a Leece Neville.

The 4th wire is for the Alt Relay which triggers a Alf Fail light on the dash.

On my chassis wiring diagram my tach gets it's signal from the ECM. You can go to the Cummins Quickserve site to see if yours get a signal from the ECM
Jim J
2002 Monaco Windsor 38 PKD Cummins ISC 350 8.3L
2005 Jeep Grand Cherokee w/5.7 Hemi
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Old 10-15-2021, 08:57 PM   #3
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Location: Braidwood Il.
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See if this helps. There are a lot of 28si posts with whatever mistakes were made and fixed.
95 Monaco Crown Royale
M11 400hp, 4060 trans.
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alternator, conversion

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