EDIT:
( OP deleted )
I have the original Walthers 130' TT (non-DCC). The control box went dead and I had to figure out a way to save the TT because replacing it would have been a pain, requiring me to pull up 22 lead tracks. There were two circuit boards, one in the control box and one under the bridge. Then the thought hit me that the only reason for those circuit boards was for indexing the TT. Since I had never gotten indexing to work reliably, I really didn't need that function. I figured why not just wire the track and the TT motor directly so I created this thread to see if anyone knew of a reason that wouldn't work. I didn't get any responses to the OP so I decided to forge ahead with my turntable fix.
I decided the simplest thing would be to gut the existing wiring and insert track and motor power up through the center post of the bridge. This required me to saw the bottom off the center post that had the concentric rings for the various power sources. I knew once I did that there was no going back. After doing that I gutted all the bridge wiring including the circuit board. The leads to both the track and the motor were too short to make a reliable splice so I soldered leads to the bridge rails and drilled a hole through the floor. I had to open up the motor housing so I could solder the leads to the motor. I wondered when I did that if I would be able to get it back together but it proved to be a rather simple jigsaw puzzle. The only difficulty was getting the cap back on the housing. I used slightly large gauge wire than was there original and I had to cut a second hole in the housing because I couldn't get both leads through the original hole. I drilled a large hole in the bridge post so I could drop the leads through the post and out the bottom. I also removed the bottom plate. I connect both the track wires and motor wires to DPDT switches, using a momentary contact switch for the TT motor.
When I got everything wired up I gave it a test. Everything worked as well as I could have hoped. I parked 4 of my steamers into the roundhouse and except for a couple operator errors everything worked well, as good as it ever had.
There are a few downsides to this approach. The loss of the ability to index was no big deal. I also have to manually reverse polarity to the TT so that it matches the lead track. This was handled automatically by the TT in its original configuration. The other thing I have to be aware of is I can't keep turning the TT in the same direction or the lead wires will become badly twisted. I have to alternate clockwise and counterclockwise rotation of the bridge to avoid this. That's not a problem.
I have one other thought that I am considering. Rather than using a DPDT switch to power the TT motor, I could use a DC power pack and use the throttle to turn the motor. That would allow me to control the speed as well as the direction of rotation. This might make it easier to line up the bridge rails with the leads as the DPDT is a little stiff. On the other hand I might just leave well enough alone. I have a working TT again. I needed something to go right because lately I have had the Midas touch. Everything I touched turned to you know what and it wasn't gold.