Inverted wires MSD 8869

DoctorC

Well-known member
Supporter 2022
Supporter 2020
Supporter 2019
Supporter 2021
Hi All,
To hook up my MSD-6AL to my Duraspark ii distributor I bought the 8869 harness as recommended by the manual. However, the harness I got has the wires inverted. Now, i paid for a harness so I want the darn thing to work as it should. So I wont be splicing the wires and calling it a day. I called MSD (holley) and they're gonna replace it.

This post is for those who get screwed in the future.

Here's the wiring diagram per the manual:
MSD-6al wiring.jpg
MSD box green (-) <--> Distributor violet (-)
MSD box violet (+) <--> Distributor orange (+)

Here's my setup using a new harness MSD-8869
20190730_215729.jpg
Top is coming from MSD box
Middle is harness
My finger is holding the distributor side of the hookup

Note that the wiring goes Green (-) -> Violet -> Orange (+)

So tonight I'll cut and splice the wires on top and then see if my vacuum advance finally works. When the new harness gets here I'll swap it out.
 
:unsure: Except the wiring isn't going to do anything for your vacuum advance. So before you start cutting and splaceing the wires know that the vacuum advance is only controlled by the engines vacuum Conections and nothing to do with the any of electronic control box or the Distribitors pick up wiring. Good luck (y) :nod:
 
This is true, but not totally correct. From what I've read/understand, the inversion of the polarity adds advance since the trigger will be on the wrong side of the magnetic pickup. So when the vacuum advance gets hooked up the advance becomes excessive quickly, hence the engine trying to shake it's way out of the engine bay.

Could be all bogus, it's the internet after all. I'll splice tonight. I'm getting a new harness in the mail anyway. So if I'm wrong, it's gonna be re-corrected shortly.
 
:unsure: So how is the polarity inverted?

By the above MSD's supplied wiring diagram!

The (DS II) Distribitors Orange wire is Positive + and the Violet wire is Negative -.

On the MSD box the Violet wire is Positive + and the Green wire is Negative-.

So therefore the MSD Violet (+ wire) connects to the Distribitors Orange (+ wire) next the MSD Green (- wire) connects to the Distribitors Violet (- wire). Which is how it's already hooked up now. I think you might be looking at the wire colors rather the were the wires go on the diagram. Good luck (y) :nod:
 
Hmm, I don't see what you see. I see my wires connected Green (-) -> Violet -> Orange (+).
Of course assuming wires in a straight line to each other are connected.

The Squared connector is the MSD box side
The round connector is the Distributor side

the square side of the harness is taking the Green (-) from the box and connecting to Violet
Then that same Violet is connected on the round side to Orange (+) on the distributor.

That's negative to positive.
 
Yes your absolutely right! :shock: :rolflmao: I finally can see it clearly now, they reversed the plug connections on Distribitor end of the 8869 wire harness. Most likely since the wire colors in the 8869 harness are Orange and Violet like on Distribitor plug end they should have been matched up to the same factory Ford wire colors and on the MSD square plug they would be correct as they are now. Good luck :thump: :nod:
 
Success!!!

So I cut the wires on the square plug side since it was easier. Spliced them together.
--------------------------
So first, the theory:
2010-12-11_001845_duraspark_stator.gif
As the center gear rotates, the magnetic pickup senses the passing of a tooth and triggers the MSD box. I had everything working because a trigger is a trigger and everything is relative. BUT if you fire off the wrong edge, you have a "built in" advance that is not showing up on your timing light, because it's triggered off the MSD Box! This is why the engine goes bonkers when the vacuum advance is plugged in. It advances MASSIVELY an idling engine. This also explains why I keep getting detonation.
-------------------------

Now, of course the engine wont start anymore. This is to be expected since I have the timing dialed in with the previous setup. With the wires inverted I'm essentially triggering off the following edge and not the leading edge of the magnetic pickup. So I should trigger when the signal starts, not when it ends.

Now to get it running again I had to advance a ton compared to previous dialed in spot. I rotated the distributor about 15° advance. It started, but rough. Then i used the timing light to dial it to 14°advance. It purred! Then for the moment of truth i plugged in the ported vac advance off the Weber. Increase in idle, still purring!! Then i dialed in the recommended 17° advance no vacuum and tightened down the distributor.

I was able to dial the idle screw way back, about a turn and a half. I think this also explains why I'm so rich. Now i have it idling happily at 650 in drive and about 900 in park.

My advance is
17° @ 670 rpm
27° @ 950 rpm with vacuum plugged in

So, in summary, wsa111 is awesome and called it correct. The damn wiring was backwards!

Now, I'm a happy camper.
 
Wsa111 is awesome. Duraspark II had a color change to the wiring in 1979 from some if the other kinds.Replacements are whitebix, and differ, as well ad having point blank mistakes in assembly line processes.

No one understands the 5 to 10 degree advance that Ford put into the Blue and Yellow and Brown DS II/ DS III. MSD does the same thing. Without all those SOL V null knobs like youd find on a theodolite...Ford had five of them, with three to control advance on certain versions of the 1979 and 80 Mustang and Capris.
 
DoctorC":30mxpqjk said:
Success!!!

So I cut the wires on the square plug side since it was easier. Spliced them together.
--------------------------
So first, the theory:
2010-12-11_001845_duraspark_stator.gif
Then i used the timing light to dial it to 14°advance. It purred! Then for the moment of truth i plugged in the ported vac advance off the Weber. Increase in idle, still purring!! Then i dialed in the recommended 17° advance no vacuum and tightened down the distributor.

I was able to dial the idle screw way back, about a turn and a half. I think this also explains why I'm so rich. Now i have it idling happily at 650 in drive and about 900 in park.

My advance is
17° @ 670 rpm
27° @ 950 rpm with vacuum plugged in

So, in summary, wsa111 is awesome and called it correct. The damn wiring was backwards!

Now, I'm a happy camper.
Good news. In my log book i show your vacuum advance if plugged into full manifold vacuum should have added 14 degrees. The other advance i sent you had only 8 degrees.
Whatever it runs super now. Bill
 
So, to wrap this up, I got the replacement part in the mail this week (thanks MSD!) and hooked it up. I checked before and it's wired correctly =)

And that's one problem solved!!!
 
DoctorC":2acl45bq said:
So, to wrap this up, I got the replacement part in the mail this week (thanks MSD!) and hooked it up. I checked before and it's wired correctly =)

And that's one problem solved!!!

I just bought this wiring harness and mine was incorrect as well... luckily I caught it (with the help of the VM6 facebook folks) before I turned it on. It was bothering me that the colors weren't lining up, so I asked the question and checked the diagram to confirm. I kind of wish I would have seen this too just to confirm, but oh well...

-Shawn
 
Back
Top