Technical Ignition RF interfering with electric speedo.

Ok I hope there is a simple fix for this Issue.
I am having an Issue with my Speedometer, it has a pulse generator at the old cable hookup.
When idling in park in the shop my speedo sweeps all over the place.
It calms down a bit while driving but after calibration I do not think the indicator is accurate.
I have been told that my MSD mounted in the car right next to the coil, and those items sharing a power source is a No-No. Add to that I am running solid core Plug wires with non resister NGK plugs. a double slap on the wrist. the car runs great but the gauge really irritates me.
Does anyone know of a material I can maybe wrap around the speedo body and signal wires to block the offending RF signals from goofing up the function of the speedo?

Here is a photo I took when I was wiring the car
The Ignition is obvious.
The Pigtails by the coil are the plug and play for the dash board wiring kit. (I can just unplug the dash and take the while thing out if needed
Also on the side of the body you will see my power strip and Grounding point. These are connected to a #2 awg (power) and a 2-O ground. Bonded directly under the body. both return directly to the battery.
Sorry apparently the file size of the photo is too large to upload successfully....
Hope someone has a simple great idea.

 

I hope this is posted in the correct forum......

 

I would think that the big block Corvette style wires, that had a woven stainless steel sheath and were grounded to the valve covers would work.
Or some reasonable facsimile there of.
KK

 

First find out if its air or cable transmitted interferance.
Feed the speedo form a separate battery with clipcables.
If it calmes down a ferrite type noise supressor ot the kind used for car audio will solve the problem.
If its air transmitted into cables try twisting the cables feeding the units (common practise in radio).
Next is using shielded cables and then grounding them in the right way is important or you can create an antenna picking up even more.

 

Flathead has it right. Twist the wires to the speedometer.

 

Or wrap signal wire in aluminium tape

 

I had the same problem. I changed to the twisted shielded speedo cable. changed to suppressor core plug wires and resistor plugs. I had to do all of these things to get the speedo to settle down.

 

Typically a pulse generator will only produce a few millivolts so any long run that's close to a powerful signal like ignition noise could be a problem.
Twisting the signal leads may help. Two other possible approaches:
- reduce the noise by going to resistor wires and plugs, and moving the noise source further from your speedo signal line, or,
- shield the speedo pulse signal line.
Cover the signal wires with a braided metal shield as close to the connections as you can get. Shrink wrap it to make sure it stays on. Solder a wire on one end of the braid and attach it to ground.

 

My flathead with Stewart Warner electronic tachometer and MSD Ignition had the same problem. We swapped the pretty red see through non resistor wires out for resistor types an eliminated the problem.