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Yea, It sounds like it worked before. Could be that it was getting power backwards through the ballast bypass, and connections corroded a bit, and now it does not get enough current.
 

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Ok, Dean corrected me. The 70's does not have the standard I or bypass terminal, instead they call the wire to the starter an I, for "coming from the Ignition switch".
 

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Discussion Starter · #25 ·
Thanks SuperBurban..I understand what you said but am still confused..I'm not sure the PO wired the original MSD correctly as I still have a ballast resistor in the mix..per Dodgeboys I shouldn't have one. That being said it has run fine for the last year or so with the new ign box and sniper..can't figure out why it won't start with the key but will off of the solenoid. Sniper says that the RPM should show the engine speed while cranking which indicates correct ign hookup(power at coil)..if it doesn't, mine doesn't, its because there's no power to the ign..when I jump the solenoid it shows RPM and fires. I'm clearly missing something.. probably something dumb.
 

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I cleaned the terminals on the ballast-didnt fix.I bought a new one for $8 just to eliminate it..didn't fix
As I said before, find the power on wire for the Sniper and power the MSD from the same wire as it's obviously powered in crank and run, neither unit draws power from it they simply get their turn-on signal from it.

FYI there is no power to the coil with a MSD except when it fires, and then it's several hundred volts, you have to check for power at the MSD box instead.
 

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Thanks SuperBurban..I understand what you said but am still confused..I'm not sure the PO wired the original MSD correctly as I still have a ballast resistor in the mix..per Dodgeboys I shouldn't have one. That being said it has run fine for the last year or so with the new ign box and sniper..can't figure out why it won't start with the key but will off of the solenoid. Sniper says that the RPM should show the engine speed while cranking which indicates correct ign hookup(power at coil)..if it doesn't, mine doesn't, its because there's no power to the ign..when I jump the solenoid it shows RPM and fires. I'm clearly missing something.. probably something dumb.
When you jump the relay, the key is still in run, not start. It sounds like you are loosing power to the ign circuit when starting, which is the normal way for the 70's ign switches to work. It took me quite a bit to track this down when I installed HEI dizzys in my 77. If you just tie the two circuits together, you will have intermittent episodes of the starter not turning off. Because power is backfeeding, and keeping the relay energized. I solved it by using a relay in parallel to the starter relay to give the standard ign bypass circuit on one truck, and by using 80's relays on the others. They call it the Bal terminal.

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Discussion Starter · #30 ·
By parallel do you mean in addition to the original..I wouldn't know how to wire that..I just replaced that as well in hopes that I was maybe losing voltage to the ign side..didn't fix..on a side note I am obviously set up incorrectly with regards to running a ballast resistor as well as an internally resisted coil..been this way since I bought this truck. How do I bypass the ballast resistor
 

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Discussion Starter · #31 ·
Ok.. following what 440 4spd mentioned I've tracked down the signal source for the msd...seems ugly to me..bat+ runs to mad from ign relay on fender and the signal wire is tapped into a soldered mess at the ballast resistor (pic)
 

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Unplug and inspect the bulkhead connections at the firewall, dropping to 5V while cranking means there's a very dirty terminal somewhere in the power circuit.
 

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Assuming the 5 volts is from the ballast bypass wire going backwards through the ballast. Since the ballast is not needed, I would test by wrapping a wire around both ballast terminals, to jump over the ballast resistor, and test.
 
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