Well, if you have an Old School car (no solid state stuff on board), then you should run solid core wire. That is best for output at the plug alright and lasts years and years.
Just filtering the power supply is easy, there is no desired signal present in the 12VDC or ground. Brute force works there...removing EVERYTHING is simple. Most electronics devices destined for automotive use already filter the incoming power and ground pretty good as part of their circuit. It's a known issue that all EE's designing that kind of stuff are aware of.
Filtering the actual speed signal to remove unwanted spikes and fuzz is difficult without screwing up the desired signal you need to keep. Remove the bad, leave the good...or at least leave enough of the good that the signal is still recognized.
The difficult problem with filtering is that filters are very frequency dependent. On an engine, the frequency is always changing as you rev up the engine. If race engines ran at one speed all the time, filtering would be simple. The filtering needs to be much different at idle as compared to 8,000 RPM for example...and everything in between and above.
The problem is radio frequency interference that is induced through the air. RFI is zapped right into the tach unit though it's housing, into the signal input wires, etc. Not an easy problem. I've worked on this issue for YEARS with varying degrees of success.
For most folks, "racing suppression" plug wire of 50 ohms per foot or less solves most of the problem and impedance that low hardly removes any spark energy. It's a fair trade.
I'm currently working on a new tach signal device for my lower drive products. A ring of magnets is added inside the drive and a small hall effect pickup unit added to the side using the timing pointer screws present on all FIE and Mallory lower mag drives made for the last 45 years or so. Works great on the bench and is much quicker, easier and more cost effective than adding a crank trigger pickup.
Spud
