Classic Industries Indash Tach needle bounces

[JohnEngland]

I purchased a in dash tach from classic industries for my 1973 charger. The tach needle bounces every so often. Hard to describe but when driving the needle drops or bounces and then corrects it self. Anyone ever have this happen. I have a R/T garage box (rev n nator box) and a firecore electronic distributor, a mopar performance chrome coil. Any help is greatly appreciated as this is very annoying when driving the car. Thanks

 

[kiwigtx]

Are you able to test out by running a piece of 'screened' single core wire from the coil to the tachometer. Ground the screen from the wire at one end (probably under dash). You may be getting spikes of electrical interference on the tachometer feed, and causing the needle to bounce.

I had the same thing happen with an electronic speedometer a few years ago. I just ran screened cable and the problem went away. This was a result of the owner wanting all wiring concealed, and entering the firewall via a small trunking - HT and all lighting /control etc)

The spikes will be coming from running parallel to the spark plug and HT leads.

 

[JohnEngland]

Excuse my ignorance...whats screened wire?

 

[JohnEngland]

Shielded wire?

 

[rlem1977]

I believe that is what he is telling you. I had that same issue when I ran my electric fan within the same loom with other wires. The tach began hopping. Moved the fan wires, tach settled back to normal.

 

[JohnEngland]

Ok
Thanks

 

[kiwigtx]

Excuse my ignorance...whats screened wire?

Screened wire - shielded...

You may need to buy a twin (two-core) screened Instrument cable - if no automotive singles are available.
Some cables have a screen as well as a drain wire, the foil is the screen, and the drain is the tinned bare conductor which connects to the ground (earth point)
TV Co-axial cable is an example of screened cable.

 

[kiwigtx]

Shielded wire?

Terminology differences...we live in a country where England and the English language has more influence.

Hey, at least we're not Chinese.

 

[khryslerkid]

Hey, at least we're not Chinese.

Chinese wire is insulated with noodles...

 

[JohnEngland]

Great...

 

[JohnEngland]

the tachometer works but as the tachometer works it has bumps that are intermittent

 

[JohnEngland]

also the wire goes from the tachometer through the fire wall along the fire wall to the electronic ignition box it does not go across the motor

 

[kiwigtx]

Chinese wire is insulated with noodles...

Egg noodle....or rice noodle? I don't want to mix flavours and textures.....might need a crunchy element.