Very nice work on this, this has been an issue for a very long time. If this works, it will save folks a lot of money on tach conversion. I hope folks who try this will post results. I have already done the tach conversion years ago.

Congrats   

I don't know how I missed this thread.

I don't recall using any thing other than the Billet ready to run MSD distributor and wiring it into the ignition circuit and AMC factory in dash 8K tachometer circuit somehow.  I wish I could remember. I will have to take a look at it to refresh my memory, I did this conversion at least 10 or 12 years ago and have been putting 1500 to 2000 miles on the car each year after, no troubles with tachometer or distributor.

Everything in the ignition system, including the tachometer were built around this.

Now an MSD distributor needs full system voltage - typically 14.2, no resistor.

The MSD distributor puts out multiple spark firings per cycle - not one like the points. The old tachometer cannot read this.

MSD sells a box for old tachometers to make a single pulse.

This voltage reduction resistor can be doing the same thing by reducing signal so only one pulse is seen by the tachometer.

A capacitor with the resistor to filter the pulses should work better, I believe this is what the expensive MSD box basically is.

Ensure the wire 12 VDC from the ignition switch does not have a resistor in it. Full system voltage to the distributor.

The MSD 8523 should have a grey wire off the distributor terminal. It may or may not operate your tachometer. If it does not then buy the MSD box for the tachometer or you can try some other "filter". But be warned that tachometers are voltage sensitive and can be "fried" easily.

MSD says to run 12v to the coil.  From the coil, you’re to run 12v to the rtr dist.   This because the DISTRIBUTOR needs 12v to operate properly.  The blaster II coil will handle 12v optimally but with the AMC tach in-line/in series with this new electronic ignition, it (tach) won’t function properly and will ultimately burn up.

        > The issue with our AMCs is that the existing wiring harness to the disturbutor took voltage from 12v to ~9.6v with the use of a resistance wire (this is the pink wire).  Other manufacturers used an in-line ballast resistor.  Whether it’s a pink wire or ballast resistor, they are doing the same function - cutting voltage to the points they the coil to keep them from burning up.

        >  AMC used the same 9.6v to operate the tach in-line from the power source (blue wire solenoid I terminal) to the coil (+ side) which is a single yellow wire. This is what the schematic above displays

So, the distributor needs 12v and you want to have your Javelin to start and turn off with the key 👍.  You need to run a wire directly to the distributor from a 12v source that is powered when the key is moved to the “on” position.   Get yourself a wiring diagram to locate the correct wire at the fuse panel and tap into it.

        >  You’re not going to find this “on” power source in the engine compartment like you have done by directly wiring from the battery.

Now, back to the pink wire.  It is directly connected to a yellow wire.  This yellow wire takes the 9.6v from the pink wire to ‘excite’ the charging system at startup.   AND, the yellow wire also splits off to connects to the double yellow spade connector.  This spade connector is the power source to the coil which fed from the “I” terminal on the solenoid thru the blue wire, to the tach and then to the coil (yellow wire).

        > I believe you have the double yellow spade connector directly attached to the coil.  If so, remove and connect to the solenoid This  is what the schematic above displays

Follow the above, I believe you will have success.

I'm a bit confused.  If the MSD box is NOT being used, why can't you simply hook it up like this and be done with it?  What am I missing?

Are you sure that the tach won't withstand 12 VDC to ground?  Think about this for a second.  What do you think the voltage is at the coil + terminal with the key on, the points open, and the engine not running?  I would bet that it is at full battery voltage.  So what is the voltage at the tach to ground?  Full battery voltage.  As the AMC tach that is being discussed is a series tach that operates from current pulses, not voltage, I am struggling with the concept that it couldn't be wired as I've shown and work.  I would also comment that the charging system (assuming this is a '69/'70 vehicle) does NOT need the 9.6 volts for proper operation as the regulator voltage sensing terminal is between the alternator output and the isolation diode(s).  The tie to the ignition system is for startup regulator supply only.

Full disclaimer:  I've worked a bit with Ford tachs that are similar to the AMC tachs but not with an AMC tach in particular.

Greg,  I fully understand and appreciate your caution in moving forward with your project.  It's hard enough to get 50 year old parts without destroying them due to carelessness or poor choices.  That being said, I think that if you configure your car as I outlined, key on, engine off, points open (or - side of the coil disconnected if you do not have your points distributor) and measure the voltage at the coil + terminal, it will be full battery voltage.  If there is no current through the resistance wire (points open) there will be no voltage drop. 

In the end it may be better to have your tach converted and driven from the tach output on the MSD distributor.  Good luck.  

As to the charging circuit, I stand by my original statement. 

I took a couple of pictures this morning, probably won't help anyone a lot, but know that the White70JavelinSST is wired like this.

Three wires from the distributor,

Orange wire to negative side of coil

Red to positive side of coil

Black to ground

Yellow wire from 70 Javelin factory in dash tachometer to positive side of coil.

Disconnected the yellow and pink (or on this car it looks tan/light brown but could be color faded) wire from the solenoid, (not used).

The distributor wire connector is ty-wrapped to the oil fill tube. There is no gray wire on this MSD RTR Billet Distributor. The underhood has never been restored on this 50 yr old car. The engine has never been out so please forgive the appearance.

The tach works fine. It has worked fine for probably ten years wired this way.

The two yellow wires wrapped in the factory thermal cover and just to the front of the voltage regultaor go to the starter side post of the solenoid. The black ground wire from the distributor is grounded to the horn relay mount (wire is seen just above the large red cable to the amplifier and between the two SS braided AC lines). The disconnected yellow and tan wire with a blue piece of tape around it can be seen in front of the voltage regulator and a bit below it.

I do not have a MSD ignition box installed nor is there some other type of tachometer adapter being used.

It's just the MSD 8523 RTR Billet Pro-Distributor, Blaster 2 coil and factory AMC 8k tachometer.

1970AMX

By adding a discreet 12v line to the dist tied into the ignition wire before the pink resistance wire, I accomplished the best of both old and new:  modern 12v dist, integrated into the original ‘70 wiring, no tach upgrade expense.

Thanks. Greg

I purchased a second MSD 8523 about four years ago for use in a fresh build 70 390.

I just opened the box to verify.

It has the grey wire, so I'll be using Someassemblyrqd's wiring method probably.

What I find interesting is the popping and sputtering some one posted about earlier. That almost sounds like a way out of time setting problem. Like 180 degrees out of time.

Someassemblyrqd,

I'll try to keep that in mind. This is one of those projects that drags on and on cuz so much other stuff gets in the way. Right now the problem is, it's way too cold in my shop.

Anyway the plan is to break in the cam on an engine run stand. So I'll wire it pretty simple, just to start and run. I may try to borrow a suitable tachometer if I can. But I'll try to keep you updated.

Armand

Have a couple question 

The car I bought a few years ago Had a  HEI install distributor

I’m putting in a MSD RTR

 

 double yellow wire on the (I)sided

 whoever wired

 in the past Some one removed these wires

They do not exist anymore!

So can use the pink and yellow installed on the (I) terminal

As they are tied together anyways???

You also show 9 volt resistance wire . - Tach  + coil

Or did you install a resistor in-line to accomplish this??

Any suggestions  welcome :)

I've read your post with great interest as I have an MSD 8519 in the box, an MSD Blaster 3 coil 8223, and MSD 8.5mm wires, all ready to install.  Several other posts indicate that I also need an MSD 6 or 7 series ignition box.  Is that the case and if so, how is that wired into your diagram.  I was under the impression/misimpression that the components I have already purchased would do the trick.  Please let me know whenever you get a moment.

Kind regards,

Ken