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7080 Tach

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dnel45 View Drop Down
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Joined: 13 Oct 2009
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dnel45 Quote  Post ReplyReply Direct Link To This Post Topic: 7080 Tach
    Posted: 19 Apr 2012 at 10:58am

Our 81' 7080 tach has been acting up recently, it would be working fine and then all of a sudden it would bounce up and down back to zero when the throttle would pick up.  Then it would work fine again.  Then today it seemed like it was registering very low RPMs, and sometimes would stick at 500 RPM and wouldn't move from there. 

Never have had a problem before, are these tachs run off of the alternator as part of the wiring harness?  Where should I start investigating?  Any suggestions appreciated.  Thanks
 
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Lynn Marshall View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Lynn Marshall Quote  Post ReplyReply Direct Link To This Post Posted: 19 Apr 2012 at 11:31am
Yes, the tach is run off of an electrical signal from the alternator.Usually the alternator is to blame if the tach is not right.I would check the alternator to be sure it is producing the correct voltage.Also,check the connections at the alternator to be sure they are clean and tight.You might even check at the rear of the engine where the engine harness connects to the cab harness.
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dnel45 View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote dnel45 Quote  Post ReplyReply Direct Link To This Post Posted: 19 Apr 2012 at 11:39am
Okay, yeah that sounds like a good starting point with some electrical contact cleaner.  Thanks. 
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Adam Stratton View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Adam Stratton Quote  Post ReplyReply Direct Link To This Post Posted: 19 Apr 2012 at 12:50pm
I second that, I have had a bad connection on my 7045 that would cause it to shoot all over the board.  Make sure your belts are tight and the pulley is still tight on the alternator while you are there. 
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