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Author Topic: Tach not working.  (Read 1011 times)
Flyboy
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« on: October 10, 2007, 01:43:00 PM »

Hi All,

My tach is not working properly.  At about 1300 RPM as I rev up the instrument drops to zero.  I noticed that when I turn on the marker lights or headlights the gauge either fluctuates or quits.  Since the two panels are co-located could it be a bad ground?   How do I find out and where should I start?

I'm not an electrical whiz and am intimidated by the sheer number of wires and the 1 1/2 inch diameter wiring harness to both panels.

I can drive the thing by sound now but it makes downshifting more challenging.  The old manuals don't even show a tachometer in the schematics only a speedometer.  Is that possible that they were originally designed that way?

Bus is a 1954 4104.

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TomC
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« Reply #1 on: October 10, 2007, 04:35:15 PM »

Practically all original buses did not have tachs.  They had colored speedos.  With a 4 speed just rev to the governor and shift.  Down shift at the same speed as the low speed of the up shift.  Check your ground-probably the problem.  Good Luck, TomC
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Tom & Donna Christman. '77 AMGeneral 10240B; 8V-71TATAIC V730.
Flyboy
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« Reply #2 on: October 10, 2007, 04:46:11 PM »

Hi Tom,

Thanks for the response...trouble is the speedo doesn't work either Shocked

Never worked for the PO while he had it.

Guess I'll try to get the ground sorted out.

Aron.
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Brian Diehl
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« Reply #3 on: October 11, 2007, 08:13:42 AM »

Here is an easy way to validate you have a good ground.  In the back of your instrument cluster find the point where all the ground wires are connected together.  Take a length of known good wire and hook one end to this point on the instrument cluster.  Take the other end of the wire and connect it directly to a good clean metal frame point.  This wire can alternatively be a little longer and connected directly to the ground on the battery.  Now start the bus and see if your problem still exists.  If the problem is still there connect the dash end of this ground wire directly to the gauge/gauges having the problems.  If the problem still exists then the ground is not the problem and the power supply should be checked next.  HTH
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