Stereo issue -- Problem REVERSING a Technics/ JL 600/3 install

[thumper88]

Just removed my JL 600 amp, Morel 4-inch midranges and crossovers, morel tweeters and German Maesto 8-inch subs from my 2009 128i coupe to install (one day) in another car.
Reintalled the stock amp first and checked it with the fancy speakers and crossovers still in -- thehead unit powered up for FM but with no sound...and it gave me an error message on head unit when I tried to run a CD.
Then proceeded to remove all the nice speakers and replace then with the factory ones.
STILL no sound. Head unit powers up, shows stations etc and doesn't indicate an error with CDs now.
But.... zero sound.
I don't think the hardware that I reinstalled is an issue. was removed with little use, and stored in a dry basement.
Did I miss some sort of re-set I should have done with the car's brain? should I have disconnected the 12v battery overnight?

[tracer bullet]

Did you piggy back the amp to the factory one, or replace it outright? Sounds like something isn't connected to the amp properly.

What level stereo do you have?

By piggy back I mean taking the signal from the stock amp, sending it to the JL, then onward to the speakers.

[thumper88]

Originally Posted by tracer bullet

Did you piggy back the amp to the factory one, or replace it outright? Sounds like something isn't connected to the amp properly.

What level stereo do you have?

By piggy back I mean taking the signal from the stock amp, sending it to the JL, then onward to the speakers.

No, they weren't piggy-backed. I took out the factory amp and ran a power cable to the battery and the ground to the bolt on inside of left rear fender above amp location.

It has been so long I forgot if the factory amp had a separate ground or its just bundled in with the rest of the harness. I see no evidence there every was a separate one. Was hoping there was a separate fuse for the amp as opposed to the head unit but the chart doesn't show anything that seems to be that.
My VIN shows S645A "BMW US Radio" and S663A "Radio BMW Professional." It is the standard amp in a lot of install photos here, and def not, say, a fiber optic one. The head unit is simple with a CD slot.

[tracer bullet]

I suppose I'd start w/ the basics - does it get 12V, etc. to be sure the amp is on to begin with. Possibly with a switched +12V as well as constant (assuming it works this way).

If it's on it sounds like a signal question. If it's off then of course dive into that next.

Hoping others have more specific ideas.