12v key on problem

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Eric Pearson

Eric Pearson

73purpule duster
FABO Gold Member
Joined
Dec 23, 2016
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Houston Texas
Good evening everyone. I have recently installed a new motor in the duster. I also installed a complete MSD ignition. The problem is that when I crank the motor with the key. The 12v key on power disipates tho around 6v. Which will not fire the ignition. I put my voltmeter on everything that has 12v key on power and all of them the voltage drop’s. Anyone have any advice for me. I would greatly appreciated it. Thanks
 
Which MSD ign? A CD ign such as the 6A or new ready to run dist? Other? More info needed.
 
Sounds like you have the "Run2" circuit disconnected.
 
Check your starter current draw also. It might be going bad & taking too much voltage from your battery.
 
You need to make certain that IGN1 and IGN2 are interconnected (easiest) at the old ballast connections. The IGN1 usually dark blue GOES DEAD during crank. IGN2 is the resistor bypass circuit, usually brown. Both these come from the ignition switch. IGN2 is the only source of ignition during cranking and must be interconnected

If the voltage is still low, and the battery is above 11-11.5V when cranking, check "the path"

Starter relay--fuse link--through bulkhead connector--to ammeter circuit--to ignition switch--back out of switch and connector--back through bulkhead---to ballast connections and to coil

Low voltage/ poor connections/ voltage drop in this circuit will ALSO case over charging

Go to MyMopar if you don't have one and download a factory shop manual, free
 
Thank you everyone for the suggestions . I will keep everyone updated when I figure it out
 
Eric Pearson said:
Good evening everyone. I have recently installed a new motor in the duster. I also installed a complete MSD ignition. The problem is that when I crank the motor with the key. The 12v key on power disipates tho around 6v. Which will not fire the ignition. I put my voltmeter on everything that has 12v key on power and all of them the voltage drop’s. Anyone have any advice for me. I would greatly appreciated it. Thanks
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With the key on run (Start 1), the power flows through the ballast resistor, which drops the voltage for longer ignition component life.

With the key in the starter engagement position(Start 2) the power flows around the ballast resistor to give a hotter spark for better/quicker cold and warm starts.

Be sure to check your grounds for quality and quantity. Your voltages seem pretty low as described. How old is your battery?

I seem to remember that MSD Ignitions don't use the ballast resistor, but it's been a long time.
 
Engine to body grounded well? It will do crazy things if its not
 
Eric Pearson said:
Good evening everyone. I have recently installed a new motor in the duster. I also installed a complete MSD ignition. The problem is that when I crank the motor with the key. The 12v key on power disipates tho around 6v. Which will not fire the ignition. I put my voltmeter on everything that has 12v key on power and all of them the voltage drop’s. Anyone have any advice for me. I would greatly appreciated it. Thanks
Click to expand...
When you say you’ve checked voltage at everything exactly what? Where are you drawing direct battery voltage to the module from? It is connected at the battery or at least the starter relay stud? Have you then tried temporarily supplying 12v from the battery to the switched 12v wire and tried starting? And how old is the battery? Been tested lately?
Assuming it’s this system:

How to Troubleshoot an MSD 6A/6AL Ignition Control
 
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The battery and starter are new. I have 3 grounds on the car and 6hey are good. I checked the power to the key on side of the fuse box. Voltage drops when cranking the engine.
 
Bad starter, or battery. It is possible. Both have the same potential to be faulty.
 
Time to start the process of elimination. With key off, Use a remote starter trigger at the relay just to spin the starter while reading voltage at the battery. Then turn the key to run, use the remote trigger to crank while reading voltage at the battery. Check voltage at the relay and up the line. I’m betting you have a bad connection(s) somewhere leading to under the dash. Excessive Resistance somewhere. Inspecting the starter cables and wires coming from the battery to the relay and or bulkhead is a good place to start to verify no corrosion etc.
 
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Re-read my post re: "the path." I've recommended a work-around for many guys. Electrically cut the IGN1 "run" wire coming out of the bulkhead. Use that to trigger a Bosch style relay, and feed the power terminal with a fuse/ breaker from the starter relay. Connect the engine bay end of the cut "run" wire to the switched contacts. You can add a switch in series with the trigger/ coil circuit to make a simple anti-theft feature
 
I wouldn’t rule out the fuse block and the fuses themselves. Corrosion/oxidation. I’ve also seen the corrosion inside the glass of the fuses.
 
I would just like to say thank you for everyone’s ideas and inputs. The problem was solved today. I located the brown wire that went to the ballast resistor and tied it together with the key on 12v wire and to the MSD box. It fired right up and is sounding awesome. Thanks again
 
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