66 Mustang electrical drain

Hi, I have a 66 mustang with an unidentified electrical drain. I have a new alt and battery, which is charging fine. When I park the car, the next day, the battery is dead. If I pull the neg cable when I park I am ok.
I pulled the (-) cable and connected a test light from the cable to the post. It lit up like a x-mas tree. With that connected, I disconnected the alternator, pulled all the fuses, and disconnected the voltage regulator with no results. I also made sure all accessories were off and the doors were closed.

If any of you have dealt with this and know what else I can try, please reply. It is just killing me that I have to disconnect the ground everywhere I go.

Btw, accessories run fine with the car on. Testing between battery posts while running I get 13-14 range. So the system is charging enough to cover the loss.

Thanks

By chance, I disconected the voltage regulator and my test lamp turned off. Once I figured out what it was, call the auto parts store and picked up my $10 part.
FYI, here is was my process of elimination.
1. fuses
2. alternator
3. starter
4. verified no disconnected-grounded lamp wires
5. voltage regulator

perty much, if you get past the fuses and your test lamp is still on, its a good bet that its your voltage regulator.

good on you, son

I dont know if you ever found out what the drain was on you mustang but the test light from the ground wire to ground side of batt will light up a test light because a ground is not a ground till you make it one (make a circuit).

yo - hella old thread + the issue was resolved.