I am rewiring my MSD 6A to bypass the transistor box on my early '74 260Z and just use the MDS box for firing. What I need to know is which wire coming off the distributer is positive and which is negative. I have a "male" and a "female" on the plug and don't know which is which. I have a factory manual and still can't find this info. Is there a way to check this to be sure?

The red wire coming off the distributor should be the positive one.

I've read that you can hook them up backward but your timing will be off and will jump around a lot, because the triggering point will be incorrect. If so, just switch the wires and the timing should steady and go back to the proper range, where it was before you started the swap, assuming that you have not moved the distributor body.

Hopefully for you, you will have a red wire. I have seen some pickup coils that have been spliced to have two blue wires, so you might have to trace the red one down from the pickup coil in the distributor.

Edited December 30, 201014 yr by Zed Head

Here is a way to test that I have seen in various places, including on this forum. It's from a writeup on converting to the GM 4 pin HEI module. I cut out the install portions,but you can read the whole thing here - http://www.sonic.net/~kyle/hei.html - if you want.

Date: Sun, 12 Mar 1995 19:49:02 -0800 (PST)

From: Andrew Levy <allevy@violin.aix.calpoly.edu>

To: Z-car <z-car@CS.Princeton.EDU>

Subject: ignition - HEI

Mime-Version: 1.0

Sender: snd@CS.Princeton.EDU

Precedence: bulk

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First you need to determin the polarity of the wires going to the

distributors pickup. Some have a red and a green wire, the red is the

positive. If you have one with two green wires or you can't tell what

color they are you will need to test them. This can be done by rotating

the dist. shaft the same direction as it would be turned by the engine and

use a volt meter to establish the polarity. This system generaters AC

current so look for a positive reading when the raised portion is

approaching the pick up and negative when it departs. You could try to

establish the polarity by starting the engine and use a timinglight to

check each combination, the one that gives you the most retarded timing

should be correct.

................

The two wires from the distributor are both green (at least by my old eyes!). However, the other end of the connector that goes into the wiring harness has a green w/white stripe and a green w/red stripe. What I will do as soon as time permits is go with the wire which connects to the green/red wire as positive. When I start it up I will check the timing and see if it has changed. Thanks, Zed Head, for the help. I will post my results later.

As it turns out, the wire leading to the green w/white stripe is positive. Good old trial and error! When it is wired backwards, the timing was considerably advanced. It idled smoothly, but didn't rev well. When I got it right, the timing was back to normal and it revved good. Thanks again for the information.