Ok, Time for bulb refresher for everyone. PS-2 3V and 5V and PS-32 use 6V bulbs. PS-1 has a lot of variations. First. If directional lighting (headlight and reverse light) are driven from the bottom of the PS-1 board blue and green connectors they are 1.5V bulbs. Otherwise they normally are 18V bulbs driven off track power and not directional. Like RK Steam engines headlight. This also applied to some RK diesels. Using Bayonnet bulbs and even GOW bulbs.
IF there is a Constant voltage board like Premier steam and diesels and sometimes RK then the bulbs are 6V. In diesel this is typically a cab light, number boards and sometimes even the marker (when driving leds there is a current limit resistor on the CV board). So trace the source of the power. If on the PS-1 board it is 1.5V, if CV board 6V, if track power 18V.
PS-1 Steam may have 18V or 6V on engine, but usually if a directional tender backup light it is driven off the PS-1 board in the tender. Marker also driven off the yellow connector on PS-1 bottom board.
Now the last variation is the DCRU which is what the op has. It is not PS-1. Some 30-xxxx-0 engines had a modified DCRU that has a 6V regulator add to the bottom of the DCRU. This provides 6V source for lights. So basically like a CV board but actually built into the DCRU. If not a modified board, the bulbs would be 18V driven off track power.
So trace wires. G
