Chas, I know it's a diesel and I know it doesn't have smoke. But Press the smoke button to turn it on and then try the lights. There have been some problems about smoke/lights interference.
Why bother with LED conversion until the problem is diagnosed? At this point, due to a dearth in data, we don't know if the problem is board output, connection between board and lights, burned-out lamps. We don't know the loco model number.
If there's no spring contacts, why doesn't Chas see a wire connector??????