tach jumps under high boost...
 

i have an early 95 miata, jumped the diagnostic box to get tach to work.

if im driving normal, lets say highway, 80+ mph, no boost, my tach reads fine.

but lets say if i 3rd or 4th gear pull, 4.5k + rpm and 8-11 psi, my tach will jump all over the place until i get under 4k rpm...

reads fine in TS.

i read about checking grounds, i ran new ground with 0 ga. wire i used for my other car audio build.

should i make a ground leading straight to the -ign