MSD Dead - Help with direction please

[ToddMcF2002]

Check your bulkhead connector you should have battery voltage at the coil during start.

I'm yet so see a jump in voltage when its cranking that's the first thing I need take a look at tomorrow I think. Thanks for the reminder. The "brown wire" (IGN2) should be 12V to the coil with the starter spinning. I can test that without a coil.

 

[ToddMcF2002]

OK so here is a quick voltage check. Probe in the ignition side of the ballast. IGN1 (Run) 3.35 volts. During cranking 9.09 volts. Just slightly lower than 9V on the positive side of the coil. Those are pretty low numbers. I may try a different battery and retest.

 

[72RoadrunnerGTX]

Looks like you are not getting ballast bypass battery voltage (Ign2) from the ignition switch or dash harness. There is some mention of running engine harness from a ’73 on a ’69 dash harness? The bulkhead connection pin-out would be slightly different from a ’69 engine harness if that’s the case. The latching is different as well. I would be verifying the correct ignition circuits correspond at the bulkhead if the harnesses are model year mis-matched as described.

 

[ToddMcF2002]

Looks like you are not getting ballast bypass battery voltage (Ign2) from the ignition switch or dash harness. There is some mention of running engine harness from a ’73 on a ’69 dash harness? The bulkhead connection pin-out would be slightly different from a ’69 engine harness if that’s the case. The latching is different as well. I would be verifying the correct ignition circuits correspond at the bulkhead if the harnesses are model year mis-matched as described.

well that’s the thing. The 9.09V is the IGN2 voltage bypass. It’s jumping from 3.35 to 9.09V. I might have a bad ground somewhere creating the voltage degradation?

 

[72RoadrunnerGTX]

I would verify that at the ignition switch then, Ign2 should be battery voltage. If your VOM is grounded correctly, could be a voltage drop across the connections, not likely a ground problem.

 

[ToddMcF2002]

I would verify that at the ignition switch then, Ign2 should be battery voltage. If your VOM is grounded correctly, could be a voltage drop across the connections, not likely a ground problem.

Agreed. I’ll try a spare battery but after that I think in dealing with some wiring problem.

 

[ToddMcF2002]

One thing I did mean to ask you folks. Without any load on the system (key out) my negative battery cable to block ground reads 0.x resistance which is fine. With key in RUN position I’m see resistance around 20-40 ohms. That’s expected right? I removed the cable and checked resistance on it seems fine.

 

[72RoadrunnerGTX]

20-40 ohms, Shouldn't be able measure any resistance across the battery cables, load or no-load. What's the voltage drop across that cable under load?

 

[Don Frelier]

You shouldn't take resistance readings on a live circuit. It's not an accurate measurement.
The meter doesn't actually measure resistance it measures voltage drop by putting a small voltage across the leads. So if the circuit is live you can't trust the reading.