I was just wondering if anybody knows why it does this and how i can fix it?

 

if you're tapping/splicing into the wire then both won't work at the same time, you need to hook them up inside the distributor and they should both work.

 

yeha... if u have a tach and u splice the cable to get signal for the RPM switch it wont work...
u gotta take the RPM signal cable for the MSD switch to inside the Distribuitor.... take the cable and put it on the (--) negative side of the coil.... juss loose the screw and tap the cable in there.... that should give u the signal u want....

 

the negative side of the coil gives an rpm signal?

 

yes
dont be hesitating about it... when i got that installed i didnt know that... a fellow HT member told me and worked... go do it now.. wont take u even 4 minutes... and come back and let us know...

 

the negative side of the coil is your rpm signal, every 4 fires is a camshaft rotation which is 2 crank shaft rotations. the msd box, tach, whatever figures that out.

 

thank you for your help guys