Msd adapter install Tach help

[J's69Mach1 17]

69 mach 351w 5sp with tach , got new msd 85840 distributor , 6al digital box . Need help on tach Adapter install. Which adapter to use ? Confused. Read alot on web and they all seem to use different adapters or methods. Does some one have this install or diagram they used that worked for them?

[jmlay 80]

I have not done this but have read many posts on this in the past. MY unprofessional opinion is the 8920 wired as described in the 8920 install doc as "Wiring a Current Triggered Tach to Points/Amplifier or Magnetic Pickup.":

 

http://www.msdignition.com/WorkArea/DownloadAsset.aspx?id=15032386438

[therebel 10]

My 6al had a place to plug the tach wire in. I didn't have to use an adapter.

[TheRktmn 15]

I have not done this but have read many posts on this in the past. MY unprofessional opinion is the 8920 wired as described in the 8920 install doc as "Wiring a Current Triggered Tach to Points/Amplifier or Magnetic Pickup.":

 

http://www.msdignition.com/WorkArea/DownloadAsset.aspx?id=15032386438

 

+1

 

I used an 8920 on my '69 fro a couple of years before converting my tach over.

It seems to be hit or miss whether it works or not, I have had as many people say the adapter didn't work for them as people saying it did.

 

Whatever you do, don't plug the tach into the MSD tach output without either converting the tach or installing an adapter.

[J's69Mach1 17]

Thank you Very Very Much for your guy's input . Very Helpful.

[therebel 10]

+1

 

 

 

Whatever you do, don't plug the tach into the MSD tach output without either converting the tach or installing an adapter.

 

Interesting, why not?

[TheRktmn 15]

The MSD puts out a 5V square wave and the OEM tach is not designed t read it. When I did it back in the 80s my MSD stopped working. It cost me shipping and $20 to get it repaired.

The others I have had sent to me for conversion post MSD tach out connection 'worked fine until I plugged it into the MSD'.

 

In a nutshell: It won't work and may fry your tach or your MSD and it's cheaper to learn from someone else's experience.

[therebel 10]

I assumed it was an aftermarket tach and not an OEM. However, I didn't know that about the OEM either so I learned something today. I wonder if the same issue could occur with an aftermarket tach. So far I haven't had an issue but I'd hate to burn up my MSD box.

[TheRktmn 15]

Most aftermarket tachs (and almost all modern tachs) are made to read the 5V square wave signal so you should be fine without an adapter. There are exceptions to almost every rule though, so check MSD's chart to see if your aftermarket tach needs an adapter.