Low volts at idle

The really big problem is usually the bulkhead connector

Where are you measuring the "9 volts?" And are you sure the meter is actually accurate?

This stuff is really easy to check out. One thing to keep in mind is that (if you still have a factory harness) that the main junction for major power feed is the factory "in harness splice" which is in the black ammeter wire in the under--dash harness, a few inches away from the ammeter. These can and HAVE failed.

Probably the best places to check voltage which are fairly easy to access is:

The black/ red wire feeds into the front and out the interior of the bulkhead connector

If the ammeter is disconnected, they must be spliced together, and the original molded connectors could be suspect. That's a high current splice and must be a good connection

Check at the main feed into the fusebox. If that is low, but the bulkhead test point looks OK, then the "in harness splice" or ammeter connections are suspect.

Make these checks with engine off, and a load such as heater blower/ headlights on. To avoid ignition problems, you can pull one end of the ballast resistor loose so that leaving the key in "run" won't hurt anything in the ignition.

To get very deep into this, we need details about what exactly you did. That is, have you changed the wiring, how did you unhook the ammeter, etc?