Ok, i see.
I replaced the adapter for a 21 pin Bachmann decoder , no sound a few years ago.
I see no problem installing a 21 pin with sound.
But i have no experience with that.

Ton

My older 2-6-6-2's have a decoder with sound incorporated.
I presume your's is of the modern type with add on sound pcb.
If so you can use the 2-4-4-2 sound add on pcb.


Ton

I milled the top of the weight away inside the fire box.
Enough space for a small decoder without sound.

Keep in mind that the bigger the speaker the bigger the sound range is.
The sounder Bachmann placed inside the cab of the Porter was hopeless.

Ton

I don't know about Bachmann DCC equipment but my Lenz Has adress 0 as a DC simulator.

Ton

Looks like it.
The only way i can imagine is to much Amps.

Ton

If i want to see if a led lights up i use the beeper/200 Ohm function.
If i want to test the diode working of the led i use the diode/2K function.
Your 188 Ohm is a mystery to me.

Ton

Did you measure the led's when disconnected  or connected to the pcb?
Always see if the led's work individually using the multimeter.
Using a power supply without any resistor can damage the led.
Voltage is not important, Current is much more.
If the led drawes more than is allowed (20mA) you will damage the led.
R=(U-U led)/0.02

Ton

Always isolate the motor.
Better be safe than sorry.
The motor is fed by a separate circuit from the decoder and does not like the "AC" from the track.

Ton

photographs.
http://www.chinesemodeltrains.com/webpics_c2.html

Ton

I didn't know they had microphones in that era?
Nice video Terry.

Ton

Galloping Goose Mark 2 

Ton

Thanks Fred , i just restored al the pictures.
http://www.amerikaanse-treinen.nl/forum/index.php?topic=369.0

Ton

Fred , i don't , won't use any picture sites so it will be difficult to show you a photograph.
The Dutch site where I published the making of the C2 has damaged pictures.
Here is a link to a page with some undamaged pictures.
http://www.amerikaanse-treinen.nl/forum/index.php?topic=369.msg8802#msg8802

Ton
I will try to restore the pictures

Seeing those C2's in action i decided to make on for myself.
I took a Bachmann HO 2-8-0 and converted it into a 0n30 C2 rust and all.

Ton

This one?
http://service.bachmann.co.uk/wp-content/uploads/2018/02/ez_man.pdf

Btw you should have asked this question in the general section and not in 0n30.

Ton