Pro Mag 20 to 8973 w/o crank trigger connection...

http://www.msdpromag.com/pdf/8973_frm25079.pdf

There's the wiring diagram.

I just called MSD, and they confused me as much as their diagram. Not sure why they can't post up a diagram for those of us without crank triggers.

Anyhow... Violet/Green from the 8973 to the same on the mag?

What of the Brown/White wire from the 8973 that shows as going to the input lead on the mag?

Mr. Canter, are you out there?

 

mag 20

ours hooks up just like the diagram. The pick-up in the mag is essentialy the same as a crank trigger for electrical connections.

 

Sorry, not to be insulting, but that's about as clear as mud. The diagram shows a crank trigger. I do NOT have a crank trigger.

 

The diagram shows the mag violet/green wire being disconnected from the "do not use" wire. Just plug those wires (violet/green to the "do not use") back in and use the mag (by turning just like a distributor) to adjust timing. Your 8973 should have a cam syn to use on cyl #1 or a cam syn for timing curves, etc. So you shouldn't need the 8164 harness shown at all.

 

Ok, that's clearing it up. Violet/Green from 8973 to the same on the mag. That's what I suspected, but I didn't want to hook up something wrong and bang the blower on startup or something stupid.

 

Thanks guys...

 

hay mike why wont it start if you use the retard we had the same prob and could no figureout why it would not start

 

Fastavenger,

Why don't you ask the experts at MSD about it...

This got me thinking too, I wonder if with the difficulty the ProMag has firing at cranking speed if creating a little additional load on the primary coil winding due to the change in rotor phase or a slight change in the signal due to the 8973 causing distortion during cranking is all it takes to keep it from firing. It would be interesting to look at the signal on a scope and see how accuratly reproduced it is (if it exists at all) during the delay function.

PS Mike, does anyone use the 8973s rev burn feature in addition to the throttle cable clip to control the burn out RPMs?

 

I think I need to learn to type faster this is the third time I have posted a response only to find Mike has typed and posted while I am still thinking....

 

Will;

I don't doubt a bit that people were/are having issues with them. I've read about the failures of them since the day I joined the forum back in Oct, 2007.

What has perplexed me is the fact that nobody published has any factual data of what actually occurred to their motor via the 8973 that caused the mechanical failure. Or, I should say, that I have not seen any published factual data.

The cabling on the 8973 is not shielded, nor is the cabling from the mag to the points box. In the limited confines of dragster or funny car, I could definitely see RFI coming into play causing misfires, and catastrophic engine damage.

With the GMC, however, we have plenty of room to separate components and critical wiring systems to keep them far enough apart to not cause issue.

Right now, I'm not even looking to do more than use the 8973 as a rev limiter, air shifter controller (class legal for what I do), and tach output for the data logger.

In the future, I may use the digital 2-step function for launching, as well as the timed timing retard to remove power at launch. That is down the road quite a ways though.

So, sorry, but I will be using the 8973 as soon as I can get it wired up.

Thanks again to Pete/Josh/Mike for the instructions on proper wiring.

 

We have used both the digital 7 as well as the 8973 for the shift function and I can tell you that the first thing to fail on these boxs if they are hit with any kind of a voltage spike is the orange/yellow shift light wire. We have lost this function on both boxes by a single accidental use of the battery charger while the MSD was powered up to make changes. What happens is that the box will sporadically ground that circuit causing the car to leave in second, its been kinda hard on transmissions...

We have since switched to using a shifter button since the driver is GunShy on letting the MSD have control of the shifter. However we are using the time/rpm (violet blue) circuit to run the shift light and it has worked flawlessly up to this point. We use it in the RPM mode of course and since you could use either to ground your shifter circuit I would recommend that you use this circuit since it seems to be more reliable than the shift light circuit.


We also mount our box in the front of the car and if I had to mount one anywhere near the magneto I would shield the box as I am sure the components inside are no better at protection from emi than the power supply of the box is at protecting the circuits from voltage spikes.

PS we do run the 8930 capacitor and I would highly recommend it to anyone who does not have it. I hope no one beat me to the board again I am typing as quick as I can....

 

Thanks BF...

Yes, that was the plan... to use the violet/white trigger wire to fire a 30A relay, which would then in turn fire the shifter. I was then planning on checking the data logger to see what actual RPM the shift occurred at, and then compensate for any time delays as needed.

The unit will be mounted under my driver's seat, which will still allow easy access to the programming serial port, as well as keeping it well away from the mag/points box and data logger.

 

Actually the PN is 8830 for the capacitor/filter.

EDB

 

Six Shooter

I agree with Will....I will never ever run an 8973 again! It cost me too much in parts and headaches!
Troy

P.S. Yes in a dragster you can not get it far enough away..and the 2 step function always went haywire to the point that we just used a normal 2 step box instead of the 8973.

 

8973

Once again, we've run the 8973 for over 5 years without a problem on a Hemi. But, we run a Mag 20, no crank trigger. The box is mounted right next to the points box and in front of Mag on frame rail. We have the coil wire completely wrapped and insulated. Grounds are very important. I don't want to offend anyone, but possibly the programming on the 8973 is too complicated for alot of racers.

 

six shooter

Hey TB314B, get a 8973 box! lol

 

I'm thinking the same thing. They're all trying to use too many retards at once, or they don't have all of the grounds in place.

I just grounded mine from the frame to the 8106 to the driver's side cyl head, then over to the pass side head, all with 14 gauge high strand count wire.

I'm happy to hear that you have yours mounted so close to the points box. MSD told me to keep the 8973 at least a foot from the 8106.

Do you have any pictures on how you insulated your coil wire?