MSD 6AL not getting 12v from ignition

[TomB]

When turning the key and the starter cranks my 12v is dropping. This is not allowing the MSD 6AL to work and the engine won't fire. If I connect this MSD ignition wire directly to the battery the engine fires. How do I find what's causing this voltage drop when turning the key?

My 1970 Fury just went through a full restoration. Is this a ground issue possibly? I also disabled the AMP gage as well since this is a known issue.

Thanks

 

[57fury440]

Isn't the red lead supposed to connect to the battery plus side?

 

[Big_John]

When turning the key and the starter cranks my 12v is dropping. This is not allowing the MSD 6AL to work and the engine won't fire. If I connect this MSD ignition wire directly to the battery the engine fires. How do I find what's causing this voltage drop when turning the key?

My 1970 Fury just went through a full restoration. Is this a ground issue possibly? I also disabled the AMP gage as well since this is a known issue.

Thanks

Questions need to be asked...

How is it wired? Where are you getting the 12 volt feed (red wire) for powering the MSD box? Is it grounded well? Clean connection to ground with no paint under terminal (fresh restoration may be a hint to this issue).

Are you measuring 12 volts at the power for the ignition box? Or are you measuring it from the ignition switch?

BTW, bypassing the ammeter will have no relevance here if everything is wired correctly.

For reference.

 

[mopar440]

Work backwards, looking where the drop stops. Or use that wire to trip a relay that sends a full 12v from the battery as a temp fix

 

[Davea Lux]

Be sure for starters, that the battery is fully charged, voltage drops off rapidly when cranking with a half dead battery. Next run a load test on the starter, if it is shorted or otherwise defective, it will drop battery voltage quickly. As noted, be sure the MSD box is well grounded. Check the specs on your unit to see if it needs a ballast resistor in the run position. If it does not need the resistor, remove it from the circuit. From there, as noted, start working backwards on the start and run circuits as applicable to see where you have 12v and where you do not. You may have a corroded firewall plug or a corroded ignition switch.

Dave

 

[TomB]

Questions need to be asked...

How is it wired? Where are you getting the 12 volt feed (red wire) for powering the MSD box? Is it grounded well? Clean connection to ground with no paint under terminal (fresh restoration may be a hint to this issue).

Are you measuring 12 volts at the power for the ignition box? Or are you measuring it from the ignition switch?

BTW, bypassing the ammeter will have no relevance here if everything is wired correctly.

For reference.

View attachment 456060

Attached is how it's wired ,circled in white is the connection. Probing at that connection point I measure the voltage drop. If I connect this wire from the MSD to the starter relay on the firewall(just for testing) I get spark from the MSD and it works fine, if I use this ignition wire from the old coil I get 12v once the key is turned, bumb the starter and the voltage drops to almost nothing and no spark.

I also checked this voltage problem from another locations directly from the fuse panel (radio fuse) and the voltage drops here as well. Seems like the whole car is dropping the 12v except for the firewall starter relay. Maybe the fuse box is getting a bad ground? Should I start pulling fuses to see if one of the other circuits is pulling the 12v down?

 

[TomB]

Be sure for starters, that the battery is fully charged, voltage drops off rapidly when cranking with a half dead battery. Next run a load test on the starter, if it is shorted or otherwise defective, it will drop battery voltage quickly. As noted, be sure the MSD box is well grounded. Check the specs on your unit to see if it needs a ballast resistor in the run position. If it does not need the resistor, remove it from the circuit. From there, as noted, start working backwards on the start and run circuits as applicable to see where you have 12v and where you do not. You may have a corroded firewall plug or a corroded ignition switch.

Dave

Hi Dave,
When I bypass the ignition circuit and go directly to the starter relay on the firewall the car runs fine. New battery, new alternator, everything charging....and working great. I will check the ignition switch.

Thanks

 

[Big_John]

Attached is how it's wired ,circled in white is the connection. Probing at that connection point I measure the voltage drop. If I connect this wire from the MSD to the starter relay on the firewall(just for testing) I get spark from the MSD and it works fine, if I use this ignition wire from the old coil I get 12v once the key is turned, bumb the starter and the voltage drops to almost nothing and no spark.
I also checked this voltage problem from another locations directly from the fuse panel (radio fuse) and the voltage drops here as well. Seems like the whole car is dropping the 12v except for the firewall starter relay. Maybe the fuse box is getting a bad ground? Should I start pulling fuses to see if one of the other circuits is pulling the 12v down?

I'm looking at the pic of the wiring and I think to give some constructive criticism, you really need to get it more under control. Somewhere you might have a bad connection or bad wiring that is causing your problem. You've got a lot of things that could be pinched or burnt.

That said, my best guess is a bad fusible link or links. Those are cheap to replace and don't let someone talk you into replacing it with a fuse.

The fuse block does not need to be grounded.

 

[LeBaron1973]

Maybe after putting in an "A-Class" effort it's time to get an auto electrician to run their eye over your work.

This should:
A) Identify the cause of your issue.
B) Provide the solution.
C) Ensure your work is safe - all wires where they need to be, all connections good and tight, everything operating optimally.

THUS

D) Eliminating any chance of an electrical fire destroying your nice car.

None of my or other members comments are intended to put you down or criticize the efforts you have made - very well done - sometimes "you can't see the wood for the trees" as the saying goes and an auto electrician should be able to (hopefully) quickly sort out the issue(s).

We wish you happy motoring soon.