TMCC wiring

The first thing to do is determine whether it is a layout wiring issue (more likely) or a ZW-C problem.  I recommend:

Disconnect the ZW-C from your layout.

If you have a multimeter, you can use it to check AC voltage output.

With all handles off, check for voltage between A and U, between B and U, between C and U, and between D and U.  All should be zero.

Advance the A handle and do the above check again.  You should get some voltage between A and U, but the other 3 should read zero.

Repeat these tests for the B, C and D handles.

If you get voltage between B and U when only the A handle is advanced, then the problem is in the ZW-C.  If the transformer passes all of the above tests, then the problem is your layout wiring.

If you don't have a multimeter, you can check for voltage using a lighted caboose or passenger car.  Connect separate wires to A, B, C, D and U.  Touch the A wire to the center rail roller and the U wire to a wheel to do the A-U test (see if the lights come on), etc.

Let us know what you find.

good advice. you might doublecheck the programming of the ZWC as it can be set up to run in a single handle mode (powering multiple posts from the A handle). Its explained in the manual. also look at the programming button to be sure it isn't sticking against the hole in the case. I've had unpredictable things happen when the program button was partially depressed.

all the best!

I have tested the voltage coming from the transformer. With all 4 throttles down there is no voltage on any of the terminals. If I advance the A throttle I get voltage on both the A and B terminals. If I advance only the B throttle again I get voltage on both A and B terminals. Does the ZW need to go in for repairs?

If the transformer is not connected to ANYTHING, there's certainly something wrong.