TCS T1 decoder with 1" harness in a HO Scale Atlas GP7 that came with a light board. Performed by JWF.
To remove the shell gently pry against the tab located underneath the loco just behind the front coupler. The shell comes off easily then. Do not remove the couplers. You will need to remove the hand rails only at the point they attach around the cab. Four out of the five went easy, there was one stubborn one that seemed to be glued in.
Photo below shows the original light board. The tape is original from Atlas. It is used to hold the LED's in place. This tape gets re used for this installation. We attempted to use a DP2X decoder for this install but found the front LED does not fit over it well enough to allow room to fit LED behind the light tube in the loco shell. Stick with a T1 for this reason.
Peel back the tape but do not remove it from underneath the light board as shown below. The original shorting plug pictured here must be removed. Gently lift the LED out of the way but do not disturb the wiring to much. It will lay back down in place the same way after the T1 decoder is plugged in.
Use a T1 decoder with a 1" harness. The decoder faces down as shown. Use a bit of Kapton tape to hold the decoder in position.
Photo below shows completed installation with T1 decoder and 1" harness. Secure the LED into position using using the original tape. The loco comes with current limit resistors in series with the LED leads so there is no need to change that.
Important Soldering Tip
Please do not use any flux either liquid or paste on the mother board. Over time, the acidic properties of liquid or paste flux will begin eating away at the fiberglass PCB and will damage it. Use only Rosin-core solder or no-clean flux approved for electronics use.
TCS recommends the use of Kester "44" Sn63 Pb37, .015" diameter Rosin-core solder. Kester part number 24-6337-0007.
You can order this solder from the following retailers:
Digikey - PN:KE1110-ND
Techni-Tool - PN:488SO6775
Other solder tips
When stripping wire, only strip a tiny little bit of the insulation. Strip no more then a 1/64 of an inch. When the wire gets tinned with solder, the insulation will shrink back more. Try to not expose any more wire then half the length of the solder pad at most. In no case should solder or exposed wire wire ever be outside the boundary of the the solder pad you are attaching a wire to.
Click here for important information on properly Stripping and Tinning wire