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Tach erratic reading


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Don't know about differences between ISL and ISM configurations but I had similar issue just before the alternator failed. 

If your ground checked out, maybe you would want to watch the alternators charging performance. The tach is wired to the stator terminal

at the back of our alternator. Something to look into, if similar.

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  • 1 month later...

My entire gauge panel will occasionally become erratic or non-operational. Traced it to the connector on back of instrument panel. Unplugged the connector, cleaned the contacts gently with fingernail file and reconnected. Worked great for several weeks. When it re-occurs I simply unplug and re-plug the connector and it is OK for some more time. I recent purchased some "Electrical Contact Grease" that next time it occurs will apply to the entire plug and receptacle.  The pins are just tin and solder coated so are prone to corrosion. The contact grease will help prevent corrosion.

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  • 1 month later...

I finally found out the cause for my tach's erratic performance. my mechanic found it by accident. He reached under the dash and found that when he touched the cable, it seemed to work just fine. So, he tightened the connection on the back of the gauge  by twisting the connector and it has worked perfectly ever since. Go figure.

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  • 10 months later...

On my tach the needle would bounce up and down by at least 500 RPM's.  I removed the hatch on the dash and with a nut driver I loosened the grounds (white wire) on every gauge, wiggled the wire and retightened them all.  I saw 2 ground blocks on the sides and did the same to all wires there.  That cured the problem and has lasted for 6 years......  I also opened the transfer switch and tightened everything I could find there.  Some were not very tight..  Make sure shore power and inverter are off for that......

 

Safe travels

Dave

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On 2/14/2020 at 6:44 AM, whaley96raw said:

I finally found out the cause for my tach's erratic performance. my mechanic found it by accident. He reached under the dash and found that when he touched the cable, it seemed to work just fine. So, he tightened the connection on the back of the gauge  by twisting the connector and it has worked perfectly ever since. Go figure.

I had a similar problem with the speedometer on my 2000 Diplomat, same cure!

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I have had this problem with the tach bouncing when the genny is running. In my case if you turn on your running lights the tach will quit bouncing. My problem was a voltage regulator that poorly handled the hand off of the load from the genny to the alternator. Every time the load shifted the tach jumped.

 

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