GP7/9 (but really a GP7)

I bought 2 of these, one in the black and white "Zebra" stripe, and one in the blue and yellow Santa Fe freight colors. Santa Fe had both paint schemes.

I like the looks, and it's currently the best selling USAT loco (It was the F7).

GP7 vs GP9

Why is it referred to by USAT as a 7/9? Well, I assume because they were very similar.

Here's a bunch of info I gathered on the web:

According to original "Diesel Spotters Guide" on pg. EMD-25, "The GP-7 has three or four louvers below the cab and two vertical rows of louvers under the radiator shutters at the far end of the long hood. The GP-9 has one or no louver beneath the cab, and lacks the two vertical rows under the radiator shutters. Presence or absence of the dynamic brake blister tells nothing, as both GP-7's and GP-9's came with or without dynamic brakes.".

GP9's had two or three pairs of louver sets on the engine room doors (the tall doors), which the GP7's did not have. Most GP9's were built with one set of louvers on the "battery boxes" (cab sub-base), but the later ones had two sets of small louvers there. These GP9's also had single 48" cooling fans replacing the paired 36" fans.

In the days before major rebuilding programs, and "phases" were determined to be chic, the GP7 had TWO vertical slit louvers under the cab, and ONE forward of the cab on the battery box access doors, on each side. As pointed out previously, the "presence or lack" of the dynamic brake blister meant diddly squat.

The GP9 had ONLY the SINGLE vertical slit louver on the battery box access door forward of the cab on both sides.
"Phase II" GP-9's had two very small vertical slit louvers on this same battery access door forward of the cab, but more importantly, had SINGLE 48" exhaust fans on the hood roof.

There were 3 phases of GP9's:

  • Phase 1 had only 4 louver sets instead of 6 in the middle of the carbody (SOO, WM, UP had these). In addition MP had the last GP7's built with identical carbody's - as was ATSF's unique GP7M 99.
  • Phase 2 had the 6 louver sets most common but still had four 36" fans (48" on dynamic brake)
  • Phase 3 had the 48" pantop style fans.

Below is a copy of the pictures on the USAT GP7/9 Manual. The only difference is the radiator louvers at the top of the far end of the long hood.

From the data above, it looks like both drawings qualify for GP7 based on the louvers under the cab (battery boxes), the 2 sets of louvers at the end of the long hood, the group of 3 louvers near the cab, and the long side sill in the center.

Here is the best GP7 vs. GP9 explanation I have ever found:


here's another source of information:

Additional items on differences: The gas cap location may be different, need to research

The handrail stanchions on a GP7 should be cast, and the GP9 had pressed steelstanchions.


First, be careful, there are a number of little "pins" sticking up from the top of the shell that can be broken off easily. (Wonder what they are?) I use a thick terry towel to prevent damaging them.

Tip: if you lay the loco on it's side, and have a magnetized screwdriver, light pressure when withdrawing the loose screw will help you take it all the way out.

First you will probably do best to remove the fuel tank because there is one other screw near it that must be removed. There are 2 small screws at each end of the fuel tank. This is the normal home for the speaker. This goes back on only one way, there is a small difference between the diameter of the 2 locating pins at each end, so if it does not go back on easily, reverse it's direction, don't force it!

There are 4 deeply set screws on each side of the fuel tank, pull these out. (swivel the trucks out of the way)

There are 4 more deeply set screws under the trucks, basically where the first and last axles are. (again swivel the trucks out of the way)

Finally, there are 2 more screws under the "inner" drivers of the truck under the long hood. To get these, you go between a wheel and the sideframe, you need a #1 phillips over 3-1/2" long, and with a skinny shaft.

Now you need to remove 4 screws that are not recessed, and they are right at the sides and ends of the battery boxes on each side of the cab. Theoretically you could pop the shell off without removing them, but it's kind of a pain, and these 4 are easy to get to.

Now you can lift the shell off carefully, but there's a lot of wires connecting things, so be careful!

Now you should unplug wires to keep from ripping them out. Stop and look first!.

Each smoke unit has 2 sets of 2 wires. There is one pair of wires for the motor, and one pair for the heating element.

The wires for smoke unit closest to the end of the long hood has it's own regulator board on the chassis, the other unit has it's regulator board right next to it, between the 2 smoke units.

You can see the smoke unit closest to the cab connected to it's board, the motor goes to the connector right on the corner, and the heater/reservoir to the connector next to it:

The "outboard" smoke unit has it's regulator board on the chassis. It also uses white and black wires:

These regulator boards have the 2 plugs labelled "motor" and "resistor" to keep from confusing the two.

"led2" on the main board is for the lights at the end of the long hood

"led1" on the main board is for the lights at the end of the short hood

"lamp" on the main board is for the cab lights

"input" on the small board is the red and black dasy chain cable from the main board to the small board to the first smoke unit board in the shell


Kadee install:

Kadee makes a kit specifically for the GP7, and it's simple to install. Here's the PDF of the install: Kadee 785


QSI Decoder install notes, using QSI prototype system:

Using prototype board, installed software was 7.0.52, installed 7.17.0, model 1008, soundset 293

Headlights are miniature lamps, 3.1mm in diameter, 5-6 volts.


Notes on electrical system:

Like many USAT diesels that have been in production a long time, there are 2 versions of the electrics. It's usually easy to tell early from late, the early versions have flat square smoke units, a heater only, no fan. Later units have a fan-driven smoke unit, you can see the fan motor, and in addition, there are boards the smoke units plug into, that supply the regulated voltage for the smoke units. In the fan driven ones, when there are 2 smoke units, often one "power supply" is on the main board or the chassis, and the second "power supply" board is attached to the roof the the body.

The unit in this article is a later type, and thus has more LEDs, where in the early units they were all incandescent bulbs EXCEPT the "classification" lights.

The GP7, like virtually all USAT diesels, has bicolor leds for "classification" lights that are red in reverse, and green in forwards. They use a 300 ohm resistor, so it appears that they can draw 60 ma. I need to verify this. The wiring is similar to the F7, so check that section for more details on lighting. Normally they run from track power.

The front and rear boards in the nose have the typical USAT weirdness:


1. the headlights appear to be track voltage, up to 18v or so, fine for DCC conversion

2. the screw in bulbs on the circuit board are 12 volts, both in parallel, judging by my testing and the 300 ohm resistor and appear to be in series with the LEDs below,

3. the leds for the classification lighs are 3 pin bicolor leds, with a common cathode.


note, when working on the board, it is wise to remove the screw in bulbs, polish up the end contact (rub on your jeans until shiny) and put some diaelectric grease in the socket... if these unscrew or vibrate loose, the classification lights are affected. They are hard to remove, try using a paper towel with a spritz of brake cleaner, so you have good friction twisting the bulb. Don't over tighten either, I apply power to see when the light goes on when inserting.

Some modifications:

I have a friend that needed to have his loco changed from battery to track powered DCC. It already had a Phoenix 2K2, so I used an NCE D408. While doing this, I wanted to change something that has always bothered me, the goofy red/green classification lights. Red was often used on the rear of a loco running with no train, but normally there was a red light in one of the headlight housings. So, not so bad, wrong location, but prototypical color. But GREEN in the forward direction for a classification light? That means that not only is the train an extra, but there's at least one more section behind this train. Well, that was not uncommon with steam trains, since they would split a long train into two or more sections because one loco could not handle it, but for diesel? All you do is add more motive power.

Another reason to replace the stock LEDs is that they are 3 terminal common cathod (negative) LEDs, which makes it practically impossible to drive them from DCC, which uses positive as common.

I found some small surface mount LEDs that are red/white. This are also bicolor, in that there are only 2 terminals. I have detailed the connections and setup in the NCE page:

The picture below shows the front 2 classification lights held in place with a bit of black silicon sealant. The lights are wired with fine gauge magnet wire.



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