Todd,

They are the same.  

PS2 were the same in both diesel and steam.  Premier and RTR.  

PS3 diesel and steam are different from each other but an RTR steam and Premier steam are the same.  Premier diesel and RTR diesel are the same.

Dave

The boards are the same but the electrical plugs may not have all the wires installed for certain lighting features.

Todd,

When I upgrade a RK 2-8-0 from Locosounds to PS2, I left the flywheel, tach, and tach tape on the motor, the engine runs fine.

Not sure what you'd find if you upgraded an older engine with guts from a RTR PS3 engine, maybe more room (no battery).

I'd buy the upgrade kit, you get all the connectors you need for any upgrade.  If you use a RailKing locomotive as the donor, you may not have all the wires you need for a proper upgrade.

One thing that is lacking in the upgrade kits is the ability to control all the lighting in many locomotives individually, that requires the mux boards. 

A PS-2 3V board is the same regardless of steam or diesel.  There are certain Premier engines that have special code depending on the features.  But gutting a PS-2 RTR to upgrade a PS-1 engine will work fine, though you may find as others have stated you need some extra wires, or have to lengthen wires.

PS-3 is not as simple.  Diesel is a separate board from Steam which is 2 boards.  One in engine and one in tender.  Additionally there are differences in Steam engine boards (Boiler Board).  The low end engines use a FET board for low current motors, and Premier engine have the Relay Boiler board for higher current motors.

Trying to convert a RTR PS-3 to upgrade a PS-1 is for the advanced and electronically skilled hobbyist.  Every thing is different from PS-2.  LED lights, wire plugs, types of harness or tether connection, tach and tach mount. 

I recommend what John say to get a kit.  Unless you have a bunch of salvage engines laying around.  G

I looked at using the PS/3 boards in an update, but as GGG says, you need a bunch of connectors and bits that you probably won't have.

One thing that is lacking in the upgrade kits is the ability to control all the lighting in many locomotives individually, that requires the mux boards.

John, is that why if someone wants to hookup a cab light they need to move pins/wires around on the plugs?  I have a RK Imperial 0-6-0 with firebox glow and cab light which look kinda cool and was thinking about adding them to my other 3 steamers.  Would the Mux board do this (is there a P/N, never seen a Mux board for sale?).

I probably shouldn't have mentioned the mux boards, because as GGG says, it will greatly complicate things.  And, they are indeed only available to an ASC tech.

I wired one into an upgrade, and in retrospect, all the time it took was not worth it, and I'm not likely to do it again any time soon!

Since I typically change things over to LED lighting, I don't even think about the maximum number of bulbs on a circuit.  The stock bulbs draw 60ma, and my LED's are in the 10-20ma range.

Many times I run the firebox glow directly from track power using a diode, cap, resistor, and a flickering flame LED from Dollar Store tea light candles.  For a larger opening, I put two side by side for an even more random effect.

If you want to do some custom wiring, I'd consider a little project that I did a while back to give me Rule 17 lighting and automatic cab light control.  I like the cab light to go out when the locomotive starts moving, seems more prototypical to me.  Also, the automatic Rule-17 lighting is nice as well.

Here's a link to that project thread.

Engine Motion Detection and Triggering Circuit

John, Did you have a part number for the connector pins?  Are you plugging the board into something or attaching wires to the connector?  G

The connector pins are .1" machine pin headers, I used matching machine pin socket strips as the mating "connector". 

I'm almost to the point of buying the connector tool for the Lionel connectors so I can use them for projects like this, but I'm still having trouble swallowing the $400+ price for the tool!

Thanks all for the info!  I just bought an early GP-9 PS-1 diesel that came in a paint scheme that will probably never be re-issued again.  Since it is a single locomotive, there wouldn't be any additional issues with wiring harnesses.  My desire is to upgrade it to PS-2.  I was giving serious thought to upgrade it to a PS-3, but from what I've read above, this is probably not a good idea.  I see a lot of PS-2 RTR diesels selling for way less than the $179 cost for an upgrade kit.  I'm not trying to be cheap, but saving some money is always good.  I will have a certified tech do the upgrade because I don't want to fry a board due to my inexperience with these items.

If you like, I do upgrades, and they come with a warranty as I am a certified tech.

Does this one have smoke? The early ones did not.  I have a Southern on the bench that is getting smoke and PS-2 added.  Found the funnel for the GPs and will install it with a PS-2 smoke unit.  G