cummins/vdo tach

[Jerry]

Hi all, I have a Cummins 6BTA with an alternator driven VDO 4″ tach. I am replacing the tach because it will intermittently stop working. The original is no longer available. I installed a FARIA unit (actually 2) and got no reading. Tach needle bumps when I switch on the key, but no rpm reading. I measured about 3v ac at the signal wire. If i reinstall the VDO it reads fine. The Faria unit is correct for alt-driven application according to their tech support. I tried switching calibration positions at the back- no joy. I’m willing to try another brand, but I can’t find anything very close to the size & style of the original. I’m hoping someone has run into something like this before & can steer me in the right direction. Thanks, Jerry

Topic

[Tony Athens]

Need to see full back & front pics showing the fan and pulley–Yes, you have a DELCO 3-wire unit–Probably a 15SI..

Tony

[Jerry]

Here are the pics:

[Tony Athens]

Look at the attached pictures.. I want something of the same quality of your alternator . Let’s ID what you have.

Tony

[Jerry]

Hi Tony, thanks for your reply. The boat is a 1998. I don’t know where to find serial or ID numbers. It has a Delco alternator. I believe(d) it was alternator driven because the wiring diagram shows it that way and there were three wires coming out of the field plug and only one grey signal wire to the VDO tach. I just discovered that the three-wire field connector has only 2 corresponding terminal coming out of the alternator. I have 3V ac on the grey wire at the tach at idle. Am I hearing you say that this engine should have a crankshaft sensor signal for the alternator? I haven’t been able to find one, but the installation doesn’t provide much access.

[Tony Athens]

What exact 6BTA do you have that had an “alternator” driven Tach? I think it would have to Pre-1990..

What exact alternator do you have? A Bosch K1?

Tony

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