Posting a few photos to show what's under the cab which is pretty straightforward
The photo are for newbies and if you've decoded a fleet of locos and have an engineering degree in model locomotive design please don't waste you time reading on…..
Body removed from chassis (in two parts) and slotted vertically back into each other
On the chassis from left to right (Cab 1 on left towards Cab 2 'at back')
Instrumentation panel and driver's seat, cab back wall abutting the printed circuit board (PCB), blank 21 pin decoder sitting atop the PCB, light switches on blue plastic housing to switch on/off lights on front or rear of loco when running on DC (when running in consist, for example), ovoid housing for speaker when sound decoder is fitted on top of some wiring to Cab 2
NOTE ON Manual LIGHT switching:
Switch 1 turns on or/off all lights on 'Cab 2' and switch '2' operates the lights on 'cab 1', (which seems counter-intuitive). If turned off, the headlight and marker lights on the appropriate end are turned off when traveling in that direction and the red marker light on that end does not illuminate when the traveling on the opposite direction.
Removing the cab detail (engineer's instrumentation, seating etc.) is simple and involves removing two screws on top of the right and left sides (behind the white wire and to the right of the red)
This exposes a double prism which is slotted into place and reflects light from the LED upwards and then forwards as the headlight (the LED is located at a lower level than the headlight itself, as the engineers cab is directly behind the headlight)
The observant reader will have observed that the white wire is disconnected in this case and is the source of the problem here. I was not certain that the MM141s had LEDs (which they do) as opposed to bulbs and hence the likelihood of an LED failing is far less than that of an incandescent (Thanks, IT)
I guess the purchase of a small wire stripper is now in order, not to mention a small soldering iron.
I am still not certain where the wire needs to be soldered exactly or whether I need to remove the bogie to do that …. ( I believe that the motor is incorporated into the bogie under cab 2 (rear wheel drive!, the only way to go:D)