MSD tach question

toddu · 02-28-2014, 06:46 PM

I have a MSD6AL (2 actually) installed, and have the gray wire connected somewhere in the 14 pin plug (timmy2 would have to help me here).

When turning on the ignition, the tach sweeps to redline. This would indicate to me that the MSD is correctly sending a signal to the tach? Or more specifically, I have the correct wires hooked up at least?

My tach doesn't work however when the engine is running :-(. I was eventually going to have the tach redone. Just wondering if I should get it done sooner than later and have it converted to work with the MSD boxes.

Todd

K Sykes · K Sykes's Garage

I believe there is a setting that does exactly what you describe - sweep the tach on start-up. What year is your car? Earlier cars need a tach "converter" that MSD sells. I used to have MSD and my tach worked fine in a 1980.

toddu · 03-01-2014, 03:00 AM

Yes, I understand the setting. I actually enabled it as it now comes from the factory disabled. My question was more - does the sweep at least indicate that I have the correct wire from the MSD box to the correct wire in the harness?

My car is an '81.

Todd

K Sykes · K Sykes's Garage

OK - better understand your question now. Three connections that matter, the tach sweep checks one of them - between the MSD box and the tach. I assume that the car is running OK? And the only issue is the Tach is not reading RPM with the engine running?

Assuming the car is running, then you are getting the second signal you need which
is the one from the "green wire" that lets the MSD know when to fire.

The last one is the coil connection that actually fires off the coil - I believe this one is "read" by the MSD to send a tach signal to the grey wire.

One thing that is out of my league, is the dual spark set up. Are both units connected to the tach? If so, could that be part of your issue?

I wish I had a better answer, think I misunderstood your original question.

mreid · 03-01-2014, 04:18 AM

Only one connects to the tach (gray MSD wire to black/purple chassis wire). Nothing connects to the coil except the black and orange wires from the MSD boxes. If the tach sweeps, but then doesn't register, you need an adapter. Which wire are you using to trigger the MSD boxes, the white wire (requires the 10 adapter) or the purple and green magnetic pick up wires (requires the 20 adapter)?

toddu · 03-01-2014, 04:30 AM

I only have 1 gray wire from 1 box connected. I have JB Racing twin dizzy, so using purple and green pickups (2 into 1 harness).

Todd

PrimeMvr · PrimeMvr's Garage

I think you need the tach adapter. I have one I bought for my 930 and didn't need it. Brand new unopened. I can send it to you and if works you can buy it, if not send it back. PM me if you want to try it.

toddu · 03-01-2014, 06:18 AM

Appreciate the offer!! Let me do a little more analysis. I may end up sending it to NHS. It was headed there eventually anyway.

Todd

mreid · 03-01-2014, 08:55 AM

That's the same set up I have, Todd. You need the 20 adapter for use with the magnetic pick up. Of course it is the more expensive of the two.

mreid · 03-01-2014, 09:56 AM

Your PM box is full, so I'll respond here. I have the same distributor. It is not the distributor causing your problem. The MSD output is not compatible with your VDO tach. The adapter is only four wires and easy to install.

toddu · 03-01-2014, 10:59 AM

PM box cleared out ;-)

Thanks for the info!!

Todd

toddu · 03-02-2014, 12:54 PM

Thanks all, got it figured out. I had a couple oil leaks (hard lines) to address. Once that was done, I started the car again and noticed the LED light on only 1 of the MSD boxes was working. A little troubleshooting, and that was the box running the tech.

I have a 2-to-1 harness for the green and purple lines. When I plugged the MSD harness into the non-working box it must have pulled apart the connection at the harness. Plugged it back up, a little electrical tape to keep it together for sure, and tach now works as expected.

Thanks again!!

Todd