Hey gang..
Trying to troubleshoot why the tach in my buddy's '71 Challenger isn't working with his MSD tach adaptor. This is what I did to isolate parts of the system:

1. I hooked up the feed from my '70 T/A with standard ignition to the feed terminal on the back of the '71's tach and used the 71's 12v feed on its own tach. I turned the ignition on the '71 and cranked up the T/A, the tach on the '71 worked..

2. I fired up the motor in the '71 and grounded the white wire from the MSD box which is the tach feed and the motor died ( so I am assuming this is what should happen ).

3. I connected the tach feed ( white wire ) from the MSD unit on my Daytona and fired up the Daytona with the ignition on in the '71, the tach didn't work.... mmmm???? The tach works with the MSD tach adaptor in my Daytona.

Is there something different between a '69 B-body tach and a '71 E-body tach? I would think fundamentally, there isn't... Any suggestions?

The four wires of the TACH adaptor are wired properly:
1. white to the tach feed from the MSD unit
2. black to ground
3. violet to feed post of tach
4. red to 12v feed

Cheers,
Troy

Hello Troy, here's a BTT for ya

The white wire from the MSD box is also used with points. Grounding it is like having the points stuck closed, and they have to open to make a spark. So it's no wonder grounding the white wire killed the engine. Dr. Christopher Jacobs pointed out in many of his write-ups that simply by putting a toggle switch to ground, attached to the wire with the same function in his boxes, would provide a rudimentary antitheft function.

R.

Yes, I agree... That is why I grounded the white wire, to see if it was doing what it is supposed to be doing. I am assuming that, if I ground the white wire coming from the MSD box ( the tach feed ) and it kills the motor, then the wire is doing what it is supposed to be doing ( that of sending a signal to the MSD Tach Adaptor )

The white wire is NOT a tach feed. It is the trigger wire for the box if you are using a points distributor or triggering it from say a GM HEI module..

If this is a Digital 6AL, the GREY wire is the tach feed.

If it is the old style 6AL, the tach output is plugged into the end of the unit.

On my buddy's 70 RT/SE Challenger, he had to order a tach adapter to make the factory tach work. This was with a Digital 6AL.

Kevin.

Tada.... Turns out my friend's 6AL is an older version than mine. I was initially thinking the tach lead was the white wire according to the MSD installation manual for the tach adaptor.. But, then took the battery tray out of the car to look at the unit and voila, there it was... The MSD of the older life had the separate tach lead port whereas the new one, like I have in the Daytona doesn't, it has the gray wire as previously mentioned. Made a wire lead to my connection by the firewall bulkhead and fired up the ole girl and the tach worked.....

What I read wrong was the white wire was coming from the adaptor and not the control unit like I see in the later version with the gray wire being the tach feed. Oh well, lesson learned and it all works now....

Next question, do these adaptors tick/click? My tach works fine, but makes a weird clicking noise. The one in this Challenger I got does the same thing..... mmm ??

Never noticed a clicking sound...But then again I never had an engine quiet enough to hear it....

I called this morning..... The tech mentioned that the clicking noise is normal. Most people probably don't even notice it....