Aftermarket tach, MSD ignition box

[77 K20]

I'm in the process of wiring up a MSD ignition box and they say the tach cannot be hooked up to the negative side of the coil. (not sure why, does anyone know why?).

Instead they say hook it up to the grey tach output wire.

I have issues with this. The grey wire needs to go to my Edelbrock E-street EFI controller. THEY say if you tee in a tach into that signal things can get messed up (won't run, won't run right, issues, sadness)

Another issue is MSD says for Autogauge tach gauges I'd need to buy a "tach adapter" which is $70!! If this is the case I'm thinking I'd ditch that tach and switch to a VDO tach to match some of my other gauges. They don't need the tach adapter.

Why can't things be more simple?

 

[Frankenchevy]

Does the edelbrock EFI controller have a “CAN Bus” output?

 

[77 K20]

Nope- no canbus

 

[Camar068]

maybe the signal is only strong enough for one output? Maybe put a pull up resistor on it? Look around on the net and maybe call Edelbrock and see what they say. That $70 adapter might be just that....a pull up resistor. Please look around the net and also make the call as I'm just guessing. Don't want you to blow anything on a whim.

Totally different setup, but on LS swaps, sometimes you have to put a resistor to the tach wire and 12V (pull up resistor setup) to get the tach to work. I had to do this on my truck to get it to work.

 

[Camar068]

Disregard above. I'm seeing the same thing your seeing on the net.....you need the adapter.

 

[77 K20]

Got everything wired in but I left my tach hooked up to the negative side of the coil. Sure enough, it doesn't work. Needle doesn't move at all.

Doesn't make sense to me to spend $70 for an adapter for a $65 tach.

Looking at the VDO tachs that will match my other gauges. These ones do not need any sort of adapter according to MSD.

The VDO tachs are meant to sink/flush mount into your dash. I need to find some sort of pod/cup to drop it into.