[81TATurbo]

I'm running my factory tach and installed an MSD 6AL box. I'm wondering about wiring. Its unclear to me but that's not unusual. I'm not good with directions or electrical. Can I just plug my factory connector into the distributor or do I have to run different wiring? There is a grey wire that comes off the box and is listed as TACH, do I need to run that wire in order to have everything work properly or is it used for aftermarket applications? Thanks in advance!

[Hesster1977]

Ok - hope this helps:

First - identify what ignition module you have:
There are three different large cap HEI distributors. To identify
which of the following diagrams fit your specific application,
remove the distributor cap and rotor and locate the ignition module
at the base of the distributor. Count the number of terminals on
both ends of the module and follow the corresponding diagram.
GM used 4, 5, and 7-pin modules in these distributors.

It is very important that you have a good 12v supply to a MSD unit, low voltage spells trouble. Best to wire the 12V+ directly to the battery, with a 10 or even 20 Amp in-line fuse.

Then reference page 14 of the instructions. If you still have questions, post or contact for additional clarification.

"Can I just plug my factory connector into the distributor or do I have to run different wiring?" This depends on what Pin connector you have, but the answer is the MSD should plug directly into the Factory distributor cap and harness.

"There is a grey wire that comes off the box and is listed as TACH, do I need to run that wire in order to have everything work properly or is it used for aftermarket applications?" I don't think any connection of the gray wire is necessary for your '81 vehicle.

See the attachment here for instructions.

https://documents.holley.com/6425.pdf

[81TATurbo]

Every thing you've listed in reference the module has been done. It was a 4 pin module in the distributor. The MSD unit has been wired directly to the battery and plugged directly into the factory distributor cap and harness. When I was asking about plugging my factory connector into the distributor, I meant the original tach wire under the hood that would usually plug into the distributor. Sorry, I didn't really specify. I was just wondering if I need to follow the other steps in the manual or if I can just plug that original tach wire back into the appropriate spot in the cap and have everything function as it should. Thanks

[Hesster1977]

Yep- I believe so, as the instructions do not show connecting the msd tach wire, I have the same msd unit on my T/A and my tach worked