I have a aftermarket tachometer installed in my truck (from JCWhitney) the tach's pickup wire is attatched to the orange wire on the coil wiring harness (my truck has TFI ignition). 2 days ago i installed an MSD ignition box (part #5400 i believe). When i installed the box i left the tach wired in the same way. Now the tach doesn't work, the needle just jumps around between 500 and 1000 rpm. How should the tach be wired in with this msd system?

BTW, the MSD box smoothed out my idle but i didn't notice much more power. But at least now i have 2 ignition systems so if the msd dies i can go back to the ford within about 2 minutes.

-Jon

 

Not sure about the tach hook up. I've seen other posts on this topic, and it seems different boxes will have different "fixes".

As for the box, play with your gaps. Most ignition changes won't help much without increased gaps. I have a Jacobs system on my 5.0 and with a box, hot coil, and good wires, etc. I have run as big as .080 gaps. Best all around performance is at slightly smaller. Just for ref, Jacobs recommends .060 as a starting point with my setup.

The biggest performance improvements on my truck were the torque at lower revs. Since the I6 makes peak torque at low revs it might be harder to feel. Either way you should net some mileage improvements. I got a little over 15% increase.

 

the msd box should have a dedicated tach signal wire coming out of it, just hook the tach up there (i know this is true for 6AL, and probably for the others as welll...)