The 7.2 volts could mean a grounded circuit, either after the ballast or the coil, maybe at the ignition module or along the way to the module. If you had points I'd say check that your points weren't closed.

Edit - p.s. the coil, or the ballast, or wires in the vicinity should be warm if current is flowing, giving that big of a voltage drop.

Just spitballing.  Hard to get a good grasp on the overall picture.

Edited November 9, 20213 yr by Zed Head

To @Zed Head's point, you could take the black/blue wire off the ballast resistor, tape it up, and check the voltage again.

I ordered just the module on the back of the switch.  Once I receive it I will install it and if the voltage drop still exists then I will try eliminating the molex connector on the ignition switch and individually connect the wires via spade lug connector to eliminate the connector.  Then, if the voltage drop still exists I will tape up the blk/blu wire and check again with it disconnected.  If there is still a drop then I will run a new wire from the ignition switch to the ballast to eliminate a partial short to ground somewhere between the ignition switch and the ballast.  After that, ????

You don't have to go all redneck with spade lugs. You can get a replacement connector from Vintage Connections. But make sure you run the one test that I suggested.

Have you looked at the C-5 connector?

1 hour ago, Dolfinz said:

Then, if the voltage drop still exists I will tape up the blk/blu wire and check again with it disconnected.

Shouldn't this be first?

You can't have a voltage drop unless current is flowing.  If you're seeing a drop at the ballast resistor that narrows things down to the ignition system.  Except for the wires that are there as part of a terminal block.  Nissan put extra terminals on the ballast that have nothing to do with ignition.

Really though, if the problem is the battery dying with the key off, you shouldn't be looking for a voltage drop.  You should just be looking for voltage.  There shouldn't be any voltage at the ballast resistor with the key off.

If anyone wants to summarize what the "current" problem is, feel free.  I assumed it's still the battery dying.

 

Edited November 10, 20213 yr by Zed Head

On 8/18/2021 at 5:52 PM, Dolfinz said:

I have a brand new alternator that clearly isn't charging the battery when the car is running. 

 

I replaced the voltage regulator as previously suggested because the alternator wasn't charging the battery when the engine was running.  I then went to test the charging circuit with the car running and it wouldn't start.  I determined there was no spark and the voltage at the coil was around 5vdc.  We've narrowed it down to possibly a faulty ignition switch so I ordered a new one.  Once I receive it I will follow all the testing mentioned to determine why all of a sudden I have no spark.  I started at the resistor and worked my way back to the switch and once replaced I will work my way back from the switch to the resistor.  I have no issues yet, at least, with the battery draining when the ignition is off.  Only when the engine is running.  The engine was starting and running fine prior to the 2 weeks it sat waiting for the new voltage regulator other than the charging circuit.  As for the firewall connections, et al C-5, I don't trust any of them as my gauges don't work and I had to completely rewire my headlights, horn, running lights and turn signals.  Once I get the engine running again I will remove the dashboard once again and deal with the remaining issues at the firewall connections.  I've never heard of Vintage connections and I'd prefer to replace the connector if possible.  I will google it.

Vintage connections has some good replacements for the connectors that use the spade style terminals. The round terminals for the gauges and dash harness to engine harness connectors were made by Yazaki (I think the spade connectors were, too.). Those connectors seem to be made of unobtanium, though you can get the terminals with different connectors from Eastern Beaver. 

54 minutes ago, Dolfinz said:

it wouldn't start.  I determined there was no spark and the voltage at the coil was around 5vdc. 

If you have the factory ignition module you should see battery voltage minus resistance drop, then it should go to battery voltage after 10 seconds (no current).  For what it's worth.  Not really sure why they call it "locking".

31 minutes ago, Zed Head said:

If you have the factory ignition module you should see battery voltage minus resistance drop, then it should go to battery voltage after 10 seconds (no current).  For what it's worth.  Not really sure why they call it "locking".

"Locking" means it is locking out the power switching circuit, so the coil never gets grounded. This is similar to why you don't want to leave the key in ON with the engine not running when you have points, only you are protecting other components.

5 minutes ago, SteveJ said:

"Locking" means it is locking out the power switching circuit, so the coil never gets grounded.

It says "lock preventing".  I know it's just a translation error.  Interesting though.  There are better terms - current lockout?  Current cut?

I got the replacement starter switch and installed it.  I also disconnected the blk/blu wire at the ballast resistor.  I checked voltage and now it's 8.5vdc at the connector to the resistor.  I also checked the voltage on the wht/red wire at the ignition switch and when trying to start and it drops from 12vdc to the 8.5vdc.  It appears that the supply voltage is dropping for some reason.  Any ideas of what could be causing this?  Can I just run a new wire to directly feed the ignition switch from battery power?  I'm also uncertain how the transistor ignition unit is related to the starting function?