Sounds reasonable for sure. A quick check would be to remove all but the main throttle and see if things run fine.
Springfield PA
That sounds like you have address 00 selected on BOTH the UT4 and Zephyr. When you select the address on the Zephyr, does it display StLo? The two throttles will fight each other, so your loco will be zipping around then it will read the stop setting of the other throttle, and stop the loco. Moving the throttle sends a new command and so it starts moving again.
When you are done running, always dispatch the address. On the Zephyr console, make sure the speed control is at stop and press Loco then Exit. For the UT4 you have to unplug, hold the Dispatch button, and plug it back in. (see also another reason I won't buy a UT4 - the first being I hate potentiometer controls - with a DT400/402 you wouldn't have this problem of the throttles fighting one another. Yet the operation of the UT4 is based on the majority responses to user polls. Sometimes I wonder about those people on the Digitrax Yahoo group). You can clear everything out of the Zephyr and start fresh by going to the back of the manual and following the procedure for OpSw 36 reset. That will clear any stored loco info from the Zephyr and allow you to start clean. Always dispatch and you won't have the problem come back.
--Randy
Modeling the Reading Railroad in the 1950's
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