OK I took some pictures.  They are not as good as Mark's but should be good enough to give everyone an idea of what the mods look like.  One change since the last post.  I decided to add the pin to the #4 engine plug solder pad on the main PCB so the whole modification is pluggable for easy backward compatibility ...or forward compatibility depending on your perspective :-) .  I also took a picture of the diagram with my mods and the jumpers I used. Using the lowest resolution on my camera, I was able to get the pictures down to 212kb - still way to large to attach here.  Any suggestions would be helpful as I've never posted pictures before.

As promised, I am posting the results of my straight DC conversion plug efforts and directional headlight quest.  It is now working on my test oval with my pulsed DC throttle.  I was able to achieve almost all of my objective (which was to come up with a plugable connector that allows an easy swap between straight DC and the original DCC decoder).  A minor exception is that I had to solder a tiny wire to the solder pad of the pin 4 engine plug receptacle on the main PCB.  I could have soldered a mail pin from my connectors and then the whole adapter would be instantly swappable but it's running and I don't want to mess with success.  So in conclusion, pins 2,3 & 5 on the main PCB need to be jumpered together.  Piins 7 & 8 on the main PCB need to be jumpered together and a current limiting resistor (I used a 1K ohm) needs to be connected to that jumper (I soldered it) and then the other end of the resistor needs to be connected to the pin 4 addition to the engine connector plug.  I would recommend the connector pin approach to keep everything plugable.  One note though.  The pins on the engine plug are numbered in reverse from the Main PCB numbering from the wiring diagram that comes with the engine.  If you position the engine so the PCB lines up with the diagram, the engine plug (on the right) pins are numbered bottom to top., so pin 4 is the 4th one up from the bottom.  Good luck all!   

 As far as getting the headlight to work via straight DC, I'm still not sure where the LED current limiting resistor is.  This is what I have managed to find out though. Pin 2 on main PCB plug goes to pin 6 on the engine plug and then to point R on the headlight LED board. Pin 3 on the main PCB plug goes to pin 5 on the engine plug and then to motor +. Pin 4 & 6 on the main PCB plug goes to circuitry on the PCB (possibly the electrical noise reduction circuitry). Pin 5 on the main PCB plug goes to pin 4 on the engine plug and then on to the + point on the LED PCB.  It is still a mystery because it is listed as "+3.3V B+ Common".  My guess is it is power to the DCC board. I may have to isolate Pin 3 on the engine plug from the main PCB as it goes to the - point on the LED PCB but I don't know where it goes to on the main PCB and I can't see the trace.  Pin 7 on the main PCB goes to pin 2 on the engine plug and then on to motor -.  Pin 8 on the main PCB plug goes to pin 1 on the engine plug and then on to the L point on the LED PCB. My next step is to insert a 1K resistor in the engine plug pin 3 circuit. I'll post the results (and whatever else I discover along the way).

Looks like 4 blobs of solder, three wires and a surface mount LED - no resistor (unless it too is surface mount and hidden under one of the wires covering the bottom (in the picture) part of the LED trace but I don't think so.  I'll add a 470 ohm resistor to my little jumper configuration and connect the headlight wire (pin 4) through it to the minus jumper.  I'll let you all know how things work out later this afternoon.
Bob

I changed the jumper plugs to a couple of plug connectors I got from Hong Cong that are exact pin fits.  I ordered a bunch them for my signals so they would be plugable and had some extras.  I'll send a picture or so to help any other wayward DC souls like me and if anyone wants to do the same thing, I'll post where I got them.  BTW, the engine now runs like a good DC runner but still needs some break in - running on my test oval now.  I see where the  funny "hitching" came from in DCC mode - there is a slight "bind" at slow speed - I hope a after a "break-in" period it will work out . .  More importantly though, where is the headlight LED current limiting resistor?  I called Bachmann and am awaiting a reply.  Thanks for everyone's help.
Bob 

Thanks Mark,
I used the diagram that came with the locomotive (back page - lower left corner).  I jumpered pins 2 & 3 and pins 8 & 7 using little PC option jumper pins and voila! It runs nicely.  Now if I can find out if the headlight has the current limiting resistor incorporated to the little PCB in the front of the engine as shown in your excellent write up on your Spookshow page or will I have to add one in my little jumper config.
Bob
P.S. You might get a kick out of a project Hans Starmans did for me using one of my old Aurora Trix (yes an original Trix postage stamp trains - I saved it in the box since 1969 because it ran like c**p).  We converted it to a L1 using the K4 shell and the mechanism from a Kato Mikado.  It runs like a dream and pulls well.

The plug arrived from Tony's yesterday and as promised I am posting the results.  The plug they sent was supposed to be a female but in fact it is a male shrouded in a guide making it look like a female.  The pin spacing is close but not exact, so no joy in Mudville.  I'll keep trying and post if any new news.
Bob

Mark, that did it! Thanks for the second post.  I was afraid to continue to pry off the shell for fear of breaking something.  Pulling the chassis forward unlocked the rear tabs.  Decoder unplugged easily.  Female-socket blanking plug-in board (pre-wired) is on it's way from Tony's Train Exchange thanks to Eric one of their technicians and his persistence.  I'll post an  update when it arrives.

Mark. One more thing.  I removed the two small screws just behind the front tender truck and the front of the tender shell is now loose but the rear of the shell still seems attached.  The truck bolster screws don't look like they are the problem and the coupler is still attached in your picture so it can't be that screw. I don't want to force things and I don't see any other screws.  What next? 

Thanks for the picture Mark.  I was hoping the DCC decoder was "plugged" in to the main board and not soldered in as indicated by a previous post.  The wiring diagram that came with the engine indicates which wires I need to run to power the motor and lights once the decoder is removed.  (Yes of course I'll make sure there is a current limiting resistor to protect the headlight  LED) so I'm getting closer.  It's obvious that the commonly used 0.100" perfboard spacing pin plug won't work - too big.  I'll take the tender shell off today and measure the pin spacing.       

Thanks for all the replies.  Still didn't the info on the blanking plug I need though.  I did mention that I was using the MRC throttle on my TEST oval.  What I didn't mention is that my layout has 48 blocks and 32 Oak Tree Systems RCI throttles with feedback and block occupancy detectors.  Each engine has a profile with horsepower, speed profiles, fuel supply, etc.  have a complete working signal system that controls the block speeds and over 300 points of digital output controlling lights and sound effects.  All of which are managed by Railroad & Company Train Controller software running on my computer.  I would have to give up much of that up in order to get that one engine to work.  I think that the price performance aspect wouldn't make sense.  One other thing, what about my other 26 steam locomotives (many of which are Key Imports brass). Several of my engines have been fine tuned by the Starmans brothers.  Their work is truly amazing and when they're done an engine runs like a fine Swiss watch.  Also what about my 62 other deisel engines and 17 Electric locomotives? All of which would have to be converted to DCC.  I wonder what that would cost.  All I really want is the info on the blank plug I can order from Digi-Key once I know the pin spacing. I'd rather not take my engine's tender apart to measure the pins without having the plug on-hand. I guess I'll try to talk to a technician at Bachmann they may know what I need to order. Thanks again for the suggestions. 

I have some new input on this topic.  I received a suggestion that I try a different throttle.  I have a Bachmann Acela set that came with a Bachmann DC throttle that was never used. I took it out of it's original packaging and swapped out my MRC throttle and guess what.  As soon as I plugged in the power pack my K4 took off at about 200 miles an hour.  The position of the speed control was set at zero and the direction switch made no difference.  As soon as it was plugged in the engine took off always in the same direction.  I then put the Acela power car on my test oval and it did exactly the same thing as did my HHP-8.  All three engines did the same thing.  The Bachmann DC throttle must be bad I guess.  No joy in Mudville today.  The K4 looks pretty in my display cabinet though.   

I'm willing to do that, but what kind of plug do I need and where can I get it?

I have a new PRR K4 that I'd like to convert to straight DC (for the time being) by removing the DCC board and replacing it with a blanking plug.  Does anyone know where I can get one to fit.  I'd rather not solder jumper wires to the main board.  I know this engine should run OK with DC but I have a MRC Tech 3 Model 9000 power pack and the on-board DCC doesn't like the TAT IV throttle pulses.  Thanks.
Bob.