Kato 1990s HO GP35s And The Digitrax DH165K0 Decoder

The Kato HO GP35 was originally released about 1992, and it was reviewed in the September 1992 MR. Kato re-released the model in 2015 with two big updates, draft gear boxes that were compatible with Kadee couplers, and a PC board with an 8-pin DCC socket. The 1992 model, which had more in common with the 1980s and 1990s Atlas Kato HO models, didn't have these features.

However, unlike the Yellowbox Atlas Kato locos, it did have cab interior detail. Although this was rudimentary in comparison with contemporary high-end models, it was an improvement, but it did affect DCC conversions of the 1990s GP35, since the front light bar ran through the cab interior and requires a different style of LED mount on a decoder. The Digitrax DH165K0 is the only decoder on the market that I'm aware of that's specifically designed to accommodate this problem with the 1990s Kato GP35.

The DH165K0 instruction sheet details rthe installation procedure, including how to solder LEDs to the decoder. A finished Kato GP35 chassis with a DH165K0 and LEDs soldered on and set up for bidirectional lighting is shown below:

The decoder has solder pads that allow a forward-facing LED to be mounted in the center of the decoder to interface with the front light bar that runs through the cab and terminates well behind the cab rear wall. The rear-facing LED can be mounted on the rear of the decoder. Some care has to be taken with both to keep them from getting in the way or either light bar, but it's possible to mount directional LEDs without cutting the light bars, unlike with the Atlas Kato HO locos.

Another problem that's partly visible in the photos above is that the cab interior can push the wires leading from the front truck to the decoder out of position when you reattach the shell, which can potentially result in the wires rubbing against the universal shaft that leads to the front truck. This can result in noisy running, so you have to be careful to make sure those wires are out of the way in decoder installation.

A problem with the 1990s Kato GP35 is also that it was meant to use horn-hook couplers, and the pilot and chassis don't quite match the old Kadee #5 style coupler box. They don't match the newer Kadee whisker-style #148 coupler box at all. You're best off using #5 style coupler boxes with the "ears" completely cut off, and then the whole assembly filed or sanded slightly thinner. You can tap the existing hole for the coupler mount in the chassis with a 2-56 tap and mount the box with a #2 machine screw.

I had a small backlog of Kato 1990s GP35s that I'd hesitated to convert to DCC until I discovered how much easier the DH165K0 makes the job. Here are two I've recently done:

You can see the LED-powered headlight especially well on UP 762. I still need to add Shell Scale UP style numberboards on this loco. Both locos are also still waiting for prototypical horns.