Be sure to check the isolation of the motor from the frame before installing your decoder. I neglected to do so and spent the better part of an hour tracking down a short between the frame and motor, causing the locomotive to take off running as soon as it got track power. I solved the issue for now with a bit of electrical tape between the frame and the motor, but I appear to have fried my decoder in the process. Posting so that others do not repeat my mistake.
Thanks for the heads-up on the shorting issue. I have a separate question about the FT's. There are different types of decoders depending on whether the model has "shoes"... which I have no clue what these "shoes" are or where to look. I'm not sure if the decoders I have will work wirh the numerous FT's I have from the first runs in 2005 through the 2015 runs.
I am fortunate you asked that question. When I went to take pictures, I found that some of the electrical tape had peeled away from the frame and was blocking the connection between the decoder feet at the motor contacts. Once fixed, the loco is now running! Now, what are the feet/shoes? This first picture shows them on the underside of the A-unit light board. To my understanding, not all of the FT units have them, since some have wires going directly to the motor. I installed the TCS IMFTA4 and IMFTB4 decoders and the instructions for them describe how to unsolder the feet from the decoder if your particular unit has motor wires instead (https://tcsdcc.com/installation/n-scale/1615). If you have the feet like I did, they go into a hole in the frame to contact with the motor contacts circled in cyan in the next picture. I annotated the electrical tap I added with red arrows. Also be careful disassembling the frame to add the electrical tape. Mine exploded on me once I removed the plastic tank at the bottom and I was not prepared for it! Spookshow also has a good discussion of the internals of the loco for more details (http://www.spookshow.net/loco/imftab.html).
Wow thanks for the reply with pix and links. What year was that FT and which TCS decoder did you use?
Not sure about the year since I picked them up off of eBay. I installed the IMFTA4 and IMFTB4 decoders in the A and B units respectively.
Newer Intermountain F units (not just FTs) are hard-wired to the motor. On older units there were 2 towers that stuck down from the light/DCC board that looked like inverted Ys....the motor had contacts that engaged those to transfer power to the motor. I actually prefer that style.......maybe not as solid electrically, but it was WAY easier to change boards.
