Tachometer needle jumping (HELP!!)

[stmpulr]

Glider, I think when I change the wires that scotch connector will be history as you stated. And the solid wire is going for sure. I will keep you guys posted as to the out come as soon as I can get to it. All is fine under 3000 rpm's above that it jumps. The motor seems to run perfect. Reving the motor at a stop seems also to be fine even above 3500 rpm.

 

[stmpulr]

I want to thank ALL that commented on this post with suggestions. I changed the harness I had made and made a new one and this time used stranded wire for the tach pulse line and it seemed to cure the problem of the tach needle jumping under hard load above 3500 rpm. Now I can keep putting around under 3000 rpm (as I usually do) and know that the tach works above that. Thanks to all.

 

[glider]

Glad you got it sorted out.

 

[stmpulr]

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I thought it was fixed but it is doing it again. Same thing. Ckecked all the areas that I could. I turned the ign. to on (motor not running) and tapped the tach housing quite hard with my hand and the needle did jump 600 rpm or so. Turned the ign. off and did the same thing (tapping on the tach) and no jumping. Bad tach??? Seems like an internal problem to me but what do I know. The dealer said he could not get the tach to work at the speedo connection when he tried to hook up the signal wire for me. (that's where the instructions for a 07 fxstb say it should go) They did get it to function when they hooked it to the #3 terminal on the ecm. Any thoughts?? Bad tach?? What is the correct part number for a 2007 FXSTB night train. (mini tach 2 5/8" black face no shift light)
Thanks guys.
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[cdn-bigfoot]

DC electricity runs on the outside of the wire and AC through the inside of the wire.

Whaa????

In practice, most of the multi-strand wires used for DC purposes have no insulation on the individual strands. In stranded wires without insulation between the individual strands charge may cross from strand to strand. Hence current will tend to preferentially flow near the skin of the bundle of wires, just as it does with a single solid conductor of similar overall diameter. Hence when the strands are thin but in electrical contact with their neighbours we can expect the effect of internal impedance to be similar to that of a solid wire of a diameter similar to the bundle of strands.

 

[stmpulr]

I got it to work correctly now. What ultimately got it to work was loosing up the mnt. cup. I loosened the screw that holds the cup to the tach (used some silicone on the threads so it won't fall out) so it does not compress the rubber gasket on the bracket as much. I felt that the tach was getting vibs. and the rubber gasket was not able to absorb them and the tach needle would than jump in the upper RPM's. I am sure that the tach may have a cracked circuit board or something and the vibrating was setting off the jumping. Loosing up the cup slightly seemed to correct the problem. It has been several weeks and I have not had the problem. I may have to spend a hundred and buy a tach sooner or later but it is working fine now.
This is just a thought (to try)if someone else is having a similar problem.