I purchased on Ebay the Trix Alco PA Union Pacific 600/601 DCC at a very decent price.
I converted it to AC, removed all the DC electronics, replaced the wheels to AC (Wheel parts from my cannibalized BR 216, BR120, ICE, the wheels are the same diameters). Runs well now with LPV4, but I cannot get the top central light to light up.
The front LED light assembly has 5 colored wires. Orange, gray, yellow, purple and black. Testing these wires with power, none of the combinations will light up the central top light. Am I missing something? All the solder points on the LED assembly are soldered with these 5 wires, so I do not think any wires are missing.
Purple wire lights up the bright side lights on both sides in front.
Grey or yellow wire gives the bottom central lights. Grey wire lights it up more brightly.
Not sure what the black wire does.
Any assistance is greatly appreciated. Thanks.
The loc runs well and I like it, just missing the front top headlights.

Thanks, that is the problem, I do not know which wire from the LED light assembly should be connected to the Lokpilot decoder white wire (for front light) (Marklin uses the gray wire for front lights). None of the gray, yellow, purple or black wires from the LED light assembly will work when connected to the LPV4 white wire.

Thanks Jeroen. I do not know how to check the LED front top light as I cannot see which wires are connected to the top front center light in the circuit board in the light assembly. What is interesting is that this is a TRIX LED light assembly and the circuit wires in this light assembly look different to the Marklin one such as the one in the Marklin Union Pacific 37610 that I have. The color coding of the wires appear slightly different also. You could be right, as none of the wires when connected, light up the center top light. Thanks,

Thanks JohnjeanB: I tried connecting the black wire from the LED light assembly to the rail track, and the other wires one at a time to the center rail track stud (red). The top center light in the light assembly did not light up. So it is very possible this LED light is burnt.
So my work-around was to connect two wires from the platen circuit board, using ESU convention white and blue wires, to a Marklin 2 pin light bulb 610080, insulated them with shrink tape, and placed it in front of the broken LED light. It shines well now. Now I have to figure out how to lower the running noise, a bit loud I might say.
Thanks everyone.

Bill,

The top light (a blinking Mars light originally) is a tricky one. Long ago I asked for help in deducing how exactly it functioned in this topic.

That was about a Trix PA-PA slave unit (which received front/rear light voltages from the master unit) where the Mars light was made to blink with an additional circuit not present in the master.

It looks as if a scheme was used similar to the one described in a link I found after further search, but using some kind of diode instead of a transistor. The additional circuit was not present in the master PA, which suggests that the components for the master's Mars light were on the decoder pcb (and which might hint at a reason your led did not light up?).

Your post reminded me of the front light assembly of a Trix PA I had lying around waiting for analysis before connecting it to lokpilot, so that is now finally on my desk for tests.

Jeroen