[SMO'KUM63]

I’m running one of those 65 repop tach gauges that is showing an incorrect RPM reading. According to MSD they said I should be running their 8920 tach adapter.

The other parts I’m running is an MSD ready to run magnetic distributor, a 6AL box and blaster 2 coil all wired by an AAW kit. The tach is connected to a pigtail that is wired to:

-12v ignition
-6AL Box tach out put wire
-negative of coil

Is my wiring wrong or is it correct and I do need that tach adapter?

Thanks for your help

 

[Mike Goble]

If the tach is meant to be used with the stock ignition you need the tach adapter. I use the 8910 model on my BMW, which has a tach that was designed to fire off the negative side of the coil.

8920.pdf (mpsracing.com)

 

[SMO'KUM63]

Thank you Mike. I believe those tachs were meant to work with the factory ignition. I just wanted to double before I spent 75 bucks on a piece I didn’t need

 

[SMO'KUM63]

How can I find out if my tach is voltage or current triggered?

 

[Nova Thug]

I would imagine that the original 65 ignition system had points and a ballast resistor.. Neither of which you are using.. Is your tach meant to be only an aesthetically 65 looking or is it a totally complete reproduction tachometer with the mechanical aspects for a 65 application..?

 

[SMO'KUM63]

It’s a repop that’s suppose to be functional.

 

[bracketchev70]

What exactly is your tach doing? Just asking for my own information. I have a 70 Chevelle with a factory tach and an MSD with the Blaster 3. I THINK its reading right. It matches my old autometer at idle but I thought it was reading high at cruise rpm. HOWEVER, I also thought the car had 3.31 gears and now believe it to be 3.55's. But now the car is apart so I can't check it again to see if my rpm is in line with 3.55 gears.

 

[SMO'KUM63]

It was just idling obviously too low for what it should. According to MSD I need their tach adapter. It’s in the mail and once installed if it looks like the revs are more credible I’ll post a reply