Hi Len: Thanks for that info... I do have a DH166PS in my DCC parts bin. Also your pic of 8Pin to 9Pin interface woke up my brain... so I built a 8Pin-9Pin interface table. You're right I can just insert an 8Pin and its plug and play, I only loose the violet Function.
I tried to attach tables, but topic 'upload' cashe is full... sorry.

Hi Len; Good question, I'll look next time I remove the shell. The Paperwork that came with the loco says DCC-Ready then has directions for both 8pin and 9pin.
If it has 9pin like in your photo (with 9th wire free), and its set into an 8pin socket (like your pic)... its then OK (green-light) to remove and put a DH165IP 8Pin decoder straight into the socket without fear of damage to the loco???
Thanks for your thoughts...
PS: what's the 9th Black wire for...? The 8Pin itself is wired to standards, with P1 being the Orange wire. 

I have a few Digitrax 8Pin (DH165IP) decoders. I have a DC Proto 2000 "DCC-ready" with a 9Pin socket. Can I use the Digitrax 8Pin in the 9Pin socket. I realize I'll loose a DCC function or two. I'll match up "P1" pin to "P1" socket hole.
Will it run OK on DCC (and DC) using a 8Pin decoder, or will it totally destroy something... and 'toast' all the electronics...?
Has anyone ever put a 8Pin DCC decoder in to a 9Pin socket? 
Thanks for your thoughts...

My grandson was shocked to learn his EZ App loco will not function using an EZ Command controller. He wrongly assumed "EZ" meant a universal HO scale operating standard...
EZ Track + EZ Command controller + EZ App Loco = operational "EZ" RR system.
EZ App will run on straight DC, not EZ Command DCC system.
Question: Can EZ App loco be converted to DCC like I do Digitrax upgrade on my other DC locomotives???

Hi Finkel;
I suggest getting an HO "Coupler Gauge" and check all couplers on your rolling stock. If any coupler is out of spec, remove it and reinstall. Check it again, if still out of spec. Replace coupler with one that will put it back into HO spec. Running different mfr railcars and building different railcar kits, will give you some out of spec couplers to adjust.
I keep on hand EZ Mate "medium length" over shank, under shank and center shank couplers for railcar adjustments. Once I had to get "long length" center shank couplers for two F7A locos.
For never fail magnetic decoupling, I use a Rix Stick magnetic uncoupler... it works fantastic in my rail-yard. Works best on rail-car "A" end as "B" with brake wheel can be tight to some locos. I always hook to loco with rail-car "A" forward.
Good luck... Keep smiling...

Hi Terry; I agree EZ Command is excellent for actual day-to-day RR operations. Once everything is Digitrax programed. The locos keep their settings and they run smoothly on EZ Command. My grandson learned quickly on EZ Command. My Digitrax isn't a handheld, just a table top unit with easy to read buttons and large screen. It plugs directly into my EZ Track for programing. You just have to have a separate maintenance track for programing or removing ALL other locos before programing the one you want. I oops and left a switcher on a siding once... I reprogrammed BOTH locos by mistake. Like launching a boat without the plug in... ya never do that twice.

Hi Terry; I have a Digitrax (Zephyr Express) DCS-52 bought 10 months ago. I love it and program all my DCC Locos with it. EZ system once I learned the process and made a 'cheat-sheet' to remind me. I've used it changing CVs on DCC locos with Tsunami2, QSI Quantum, ESU Select, ESU LSS, ESU Digital, and of course Digitrax DCC ready plug and play 8 pin, 21 pin, etc. Converted many of my DC to DCC ops with Digitrax DH166MT, etc. Once programed, I run my set-up (switchyard) using my EZ Command with 1-9 locos. I made the DCC address for each loco the 'last number' in their road number (CB&Q #338 is DCC address "8") (Great Northern #152 is address "2"). My computer stills are nil, I'd mess-up bigtime and can't afford to destroy one of the locos. Sounds like you're in for a good time making them run your way. I needed to quiet my sound down as they all came set at FULL volume and loud horns. Also they were speed set for fast running... and I need slowwwww yard speeds. Digitrax makes it EZ to adjust CVs.

Hi Trainman; Thanks for that light-car coupling issue. Never thought TT might present rail yard switching problems with lighter weight railcars. My set-up is ALL rail yard running switchers and small Geeps. I'll stick with HO for now... unless I can get hands-on TT proof positive on yard switching. Thanks for your advice... I learn something new every day. 
Different issue, looking at Sinclair Antennas to go on some locos and way-cars. I see Cal Scale, Details West and Custom Finishing offer some possible Sinclairs. Does anyone have positive (green light) or negative (red light) on "quality" of these mfr products? I bought air horns once (forget from whom) and they were garbage quality, totally unfinished even molding was inferior and would've taken too many hours to re-build and re-finish, before I could paint and attach them to the loco. Anyone's thought...
Quality finish: Cal Scale red or green??? Details West red or green??? Custom Finishing red or green???

Hi Trainman and Quentin; I run 64' of track on 4'x 8' with double oval "X" design and 4 sidings. [Figure if I go into TT scale, I can do 100+ feet of track.] I have mostly 32'-40' rolling stock and a few 50' which I remove unless needed. Have a nice set of Seaboard 50' ice refers. I run 30 locos with 10 Geeps, 10 switchers and 10 misc including a nice little ML8 Plymouth. About half are DC and half DCC.  Grandson is getting really good at controlling 2 locos running, while building and spitting trains using EZ-Command. [His first train was a Great Northern DC 0-6-0 w/ log car, pax car, box car, bobber caboose.]
We are all blessed to have such a great hobby... Keep smiling... 
 

Thanks Len and Trainman... I'll see how this plays out in the next 3-6 months. I do remember Hornby from years ago in 0 or 00. This TT is a new road to go down. I enjoy learning new things and seeing whats over that next hill. TT Scale just might be that next hill for me to climb.
Thanks again... Stay safe, keep smiling...

Hi Trainman; You hit the nail on the head and why I went with early era Diesel. More Mfr availability in medium and small road names. Also older era Diesels were shorter LOA and a large selection of diesel switchers on the market. Size (length) matters on many layouts. I try to stay at NTE 40-50' rolling stock length and my longest loco is SD9 U25B size. GPs fit all my curves. Anything too long is just trouble on my curves and turnouts.
Hi Terry, loved that NW5... one reason I model Great Northern is small diesels which are somewhat unique.

Hi Trainman... Thought about your questions on TT and why I'm interested. [1] HO size is limiting my usability on a small area set-up. [2] I really thought about N scale and picked up a few Locos to see if that might work. Realized doing the maintenance and rolling stock quality improvements, N scale would be too tiny for my old eyes. I thought about (H)On30 but 9mm track would be problematic while still running 1:87 scale body. I was asked to look into TT 1:120 and after reviewing data, discovered it might just work. I'll get some rolling stock to see reality of doing maintenance with my old eyes.
I really like Bachmann EZ-Track silver and if it was available in TT 12mm I'd be getting it for EZ set-up and take-down, switches, and using my current DC and DCC control systems.
If I decide to jump into TT scale I'd be throwing $4-5k into a new set-up (track, locos, rolling stock). Many others I've discussed this with are also interested in down-sizing from HO to TT.
Maybe the future is here... we'll see. 

Thanks Len... Great TT info on different TT gauges. You solved my UK 3mm brain twist, now it makes sense.
I'll add all the info you shared in my TT file.
What's your opinion on Hornby Loco and rolling stock quality?
Do you know of any loco mfr for US roads like Great Northern or Burlington (CBQ)?

I've seen lots of TT rolling stock on EU sites, its very popular in many countries.
TT Scale Train Info; TT Scale is 1:120
TT (Table Top) scale is 27% smaller than HO scale and 33% larger than N scale.
TT Scale is 73% the size of HO Scale.
TT scale proportion is 1:120 which is 1/10" = 1' full size, so that means 1" = 10' actual feet. 
HO Scale layout done in TT Scale takes 54% of the space.
Length of TT GP-7 Locomotive 56ft 2in. = 5.62 inches. Length of TT 40' Box Car = 4.0 inches.
Also TT rail gauge is 12mm down from HO 16.5mm

Scale   Ratio    Gauge   (between rails)    
N           1:160   0.353 inch   (9 mm)   
TT           1:120   0.472 inch   (12 mm)   
HOn2    1:87           0.276 inch   (7 mm)   
HOn30     1:87           0.353 inch   (9 mm)   
HOn3    1:87           0.413 inch   (10.5 mm)   
HOm    1:87           0.472 inch   (12 mm)   
HO            1:87           0.65  inch    (16.5 mm)   

I learn something new everyday, and TT education is just starting.
Thanks everyone for your thoughts... 

I thinking of switching to TT (table top) scale (1:120) from HO (1:87).
I run 64 feet of HO track on 4x8 sheet of plywood... I think I can double that by going to TT scale. I could also set-up TT in the RV.
Does anyone have experience with TT scale???
I would also buy TT gauge EZ-Track if and when Bachmann makes it. Lots of chatter on TT scale on other forums.
Any thoughts...