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MSD ready to run and 1970 Tach |
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Amc wannabe 
AMC Apprentice 
Joined: Jan/08/2014 Location: DE Status: Offline Points: 86 |
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 Topic: MSD ready to run and 1970 TachPosted: Sep/21/2020 at 11:57am |
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Good morning everyone,
I am finishing up a whole build and looking to get on the road before winter and am smacking my head against a wall trying to get this tach installed. I am using the MSD ready to run and have searched the forum to find answers with limited success. The only thing I have found for when the person is only using a ready to run distributor is a hand drawn sketch but with plenty of back and forth that an electrical novice such as myself gets lost really quickly. Could someone please help me out? I attempted to wire as the drawing suggests (and how I interpret it correctly or not) as such 1. the msd red wire and key on wire being connected without touching the coil positive (the “eliminate this” comment appears to say don’t bring them to the coil anymore?) 2. From the coil positive I run through a ballast resistor and onto the tach negative. From the tach negative I run to a wire that is energized when the key is on( in the diagram is says the ignition post on starter solenoid but seeing as I was just testing to see if it would work I took a lazy way because I’m using the mini starter under the car and would only want to get down there if it actually worked) My results were that the vehicle was unable to start, it would spin and sputter and when I let the key off for a bread moment sounded like it wanted to go. I tried a few more variations but haven’t gotten anything to work. Let me know what you guys have done, could really use the help to get it on the road. Thanks! PS sorry I didn’t attach the picture, I can’t seem to figure it out.
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Amc wannabe
AMC Apprentice
Joined: Jan/08/2014 Location: DE Status: Offline Points: 86 |
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Posted: Sep/21/2020 at 12:01pm |
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troutwilly
AMC Addicted 
Joined: Sep/14/2007 Location: Carriere, MS Status: Offline Points: 994 |
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Posted: Sep/21/2020 at 7:25pm |
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Looking at your sketch, your coil is only going to get power when the key is turned to the start position. That is what the "I" (Ignition) terminal on the starter solenoid is for. It provides power to the coil when the key is in the start position. Once the key is moved from start to run, the power to the coil must come from a power source that is on when the key is in the "run" position. Most, if not all, power sources in the "run" position go off when the key is turned to "start" to provide max power to the starter. On a stock setup, that is via a yellow wire from the voltage regulator. Some distributors require a ballast resistor but looking at the instructions for yours it apparently doesn't. That would be the "eliminate this" in the red wire at the coil on your sketch. I don't know if you can use the same power source for the distributor and coil, but I think that's what you need. Another but....I would wait for someone else to chime in to verify.
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Bill O.
70 AMX |
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greenhue
AMC Apprentice
Joined: Apr/12/2020 Location: Whittier Status: Offline Points: 41 |
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Posted: Sep/21/2020 at 7:54pm |
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I have a 70 Javelin that I ran MSD coil and MSD box and Petronix but I used a MSD tach adapter pn 8920 that let the factory tach to function. I now use HEI with a different tach as I could not get the factory tach to work with HEI.
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bikerfox
Moderator Group 
Joined: Aug/02/2009 Location: USA Status: Offline Points: 4473 |
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Posted: Sep/21/2020 at 11:51pm |
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Page 7 shows a gray wire coming from the dizzy wiring harness. I have the same
dizzy as you, but no gray wire. If you have one, apparently, it's connected to your tach wire. |
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1969 Rebel SST (1970-1987)
1968 AMX (2005-2011) 1969 SC/Rambler (2011-2019) 1970 Javelin (2019 to ?)"Jane" |
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6PakBee
Supporter of TheAMCForum 
Charter Member Joined: Jul/01/2007 Location: North Dakota Status: Offline Points: 5458 |
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Posted: Sep/22/2020 at 8:58am |
Disclaimer: I do not own the MSD distributor in question nor do I have any experience with it. But reading the description of the tach output this sounds like something suitable for a voltage triggered tach, not a current triggered tach like the stock AMC version. Tach Signal: The Ready-to-Run Distributor features a Gray Tach Output wire which provides a clean signal for most tachometers and even some aftermarket fuel injection systems. The signal output is a 12 volt square wave, 20° duty cycle. This wire is also responsible for programming the built-in rev limiter.
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Roger Gazur
1969 'B' Scheme SC/Rambler 1970 RWB 4-spd Machine 1970 Sonic Silver auto AMX All project cars. Forum Cockroach |
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Someassemblyrqd
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Joined: Jul/02/2012 Location: Renton, wa Status: Offline Points: 458 |
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Posted: Sep/22/2020 at 1:55pm |
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Wannabe - the posted drawing is my work of art and how I wired my ‘70 AMX. I drew this schematic out because I specifically wanted to use my unaltered factory Tach.
First, the blue wire coming from the “I” solenoid to the tach and yellow wire coming from the tach to the coil is standard wiring per the TSM, nothing new here. This provides the current trigger feed the coil is pulling from the “I” side. Now, I assume you are using a blaster II coil, which is what I’m using, but this should work with a stock coil. The coil receives a full 12v at start. Once started, the coil receives 9.6v because the resistor wire is now feeding power to the blue wire at the solenoid. The coil will function with 9.6v. The tach operates at the 9.6v. Continuous 12v feed to the standard tach is sure death. Second, the MSD instructions says to use 12v to the coil, for two reasons: 1) to feed power to operate the coil and 2) to feed power to the RTR dist directly from the coil. As noted, above, the coil can operate at 9.6v. The RTR can not operate at this low level voltage. It needs the full 12v. This why, on the schematic drawing, I note eliminating the power feed from the coil to the RTR dist. Therefore, to feed power to the dist, you need to create a full time 12v feed when the key/ignition is turn on. For my dist power source, I took a feed off the ignition wire at the fuse panel It’s a full 12v prior to becoming 9.6v after the resistor wire (pink wire). The ignition wire is hot when the key is on, dead when the key is off. My AMX has been operating in this configuration for 2+years, and the tach is functional, as well. You do not use the grey wire from the dist to operate the factory tach. You will only use the grey wire if you update your tach to a Modern wave form feed. There is no MSD tach adapter for use with the RTR dist, unless you use an A6 box. Give this a try, hope this description helps with your build. Greg |
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Greg E.
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wyatt
AMC Fan 
Joined: Nov/15/2014 Location: Victoria Status: Offline Points: 19 |
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Posted: Feb/06/2021 at 10:00pm |
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Troutwilly is correct. The "I" post on the solenoid is only powered when the key is turned all the way to start. The 2 yellow wires that are attached to the "I" post I think is really one yellow and the other is pink. My pink wire is now white due to its age. According to the TSM wiring diagram, there was a blue wire from the "I" post and this blue wire was spliced into the "Pink" and "Yellow". When using an MSD distributor, it is recommended to install an MSD relay PN 8961. You would feed this relay with a clean pure source of 12V power, which I did from the battery side of the solenoid. This relay will be powered by the yellow wire from the ignition switch. On my 390 I spliced a new yellow wire into the spliced pink wire located under the dash near the steering column, I removed the pink resitance wire altogether. To ensure the relay openned so as to shut the engine off, I installed a 6A 200V diode onto the 2 yellow wires located at the splice that I removed the pink at. There is a back feed from the ALT light that will keep the relay closed so the engine will actually run on. The output 12V from the relay will go to the blue wire to the Tach. The yellow wire from the tach will go to the positive of the coil with the red from the Distributor. The negative coil will have the orange from the Distributor. I have just installed this to my 1968 AMX and everything is working great. Hope this helps. |
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bikerfox wrote: