John,
Can the coupler in the tender and the Led share a common ground? I only have five wires in the tether and using a second speaker would take two of them?
They can share a common ground, note that the positive side of the LED goes to ground using TMCC. Also, you will need a dropping resistor, 470 ohms is a good pick for TMCC. I also add a diode to protect against reverse voltage.
John,
I am up to the challenge on the Veranda of having the tender speaker work. I need some clarification on how to get the job done. I have 5 wires in the tether. Two will be used to connected the audio. One will be for the coupler and one will be for the LED. The fifth wire will be the common ground for the coupler and LED.
1) What port on the Cruise Commander board will I connect the common ground - the common port for the LED or one of the coupler posts?
2) I understand I need to use 2 - 16 ohm speakers to get sound if the tender is not connected. Will the existing 8 ohm speakers work wired in parallel if I always have the tender connected? Why do you need to use 16 ohm speakers to get one to play independently?
3) Does it matter what side of the LED I connect the resistor and diode - positive or negative lead.
4) Will the 1N4003 diode be a good choice for the diode connected to the LED? I have been using a 470 ohm resistor for my headlight and backup light LEDs, but I have not been using a diode. I assume the diode is needed in the case of the common ground. Am I correct in saying I would not need a diode when connected to the Cruise board LED ports and not using a common ground?
Thanks
Mark
1: You can just connect any frame ground to the commons.
2: You want 8 ohms impedance, two 8 ohm speakers in parallel yield 4 ohms. Two 16 ohm speakers in parallel yield 8 ohms. It's not a problem to have more impedance as that just reduces the sound level. Having less impedance risks overloading the audio amp.
3: Of course it does, LED's and diodes are polarity sensitive devices! From the headlight output of the Cruise Commander, connect to the cathode of the diode (stripe). From the anode of the diode, connect to the short lead of the LED (negative). The long lead of the LED (positive) goes to frame ground.
4: The 1N4003 is fine, that's what I generally use, and the 470 ohm resistor is also good. The reason for the diode is when the R4LC comes up in conventional mode, it outputs full wave AC on the lighting outputs. The peak reverse voltage of around 14 volts exceeds the 5-7 volt reverse voltage rating of the LED, the diode prevents damage.
John,
I have a few more questions. Does it matter if the 470 ohm resistor is before or after the diode in the LED circuit? I usually use ERR coil couplers, but the Verada needs the long MTH couplers. I find the MTH couplers get stuck open when wired to ERR boards. Is there a wiring trick to get the MTH couplers to work with the ERR board? I did not know about the diode in the LED circuit and my Gas and Coal turbine do not have the diodes in the circuit. The engines work fine. Should I wire in a diode in those engines in the LED circuit?
Mark
The resistor can be anywhere in the circuit.
Make SURE you're using the PS/1 couplers with the TMCC, the PS/2 couplers are too low impedance and they'll fairly quickly cook the coupler triacs.
As far as the diodes, I never used to use them with LED's, but after a year or so in service, several locomotives had headlights die. Haven't lost any since I added the diodes.
John,
I am learning so much from your answers. Why does TMCC boards require the LED positive side go to ground on TMCC? I know it works this way, but I do not understand why?
Mark
Because they designed it that way! 
Seriously, the reasoning that kinda' makes sense is the smoke triac outputs positive voltage, so they made the lighting traics use the negative side of the waveform to minimize the DC bias imparted to the track. That's the "logical" answer, but I have no idea if that's the actual reasoning they used.
John,
I sent you an email. Please reply with an address to mail the ERR boards for repair.
Thanks,
Mark
