I think you may be understandably confused by the terminology in this area.
The wiring in your loco (not having seen it but I believe this to be the case) enables you to have working lights at the front and rear, and something called "function output 1" or "function 1" or "F1 terminal" even (confusingly) F1. This is not the same as function key 1 on your controller. This function output 1 is usually manifested as a pair of pins or socket on the circuit board, into which you can plug some device. Usually it is used for a smoke generator.
These (F1, front light, rear light) are all independently switchable. With early MTS and the 55021 decoder you can use the "light" button or any of the keys 1-8. The confusing bit is that these keys are sometimes called F1, F2, F3 etc.
The keys that control function output F1, front light and rear light are configured in CVs 51, 52, and 53. You can choose to have the "light" key control any of these. So if you wanted you could have the "light" key controlling function output 1, function key 1 turning the front lights on and function key 2 turning the rear lights on. Not sure why you would do that but you could. The important thing to understand is that the relationship between the key you press and the thing that controls is defined by you in CVs.
The usual way to set this up is so that the "light" key turns the lights on. So CV52 and CV53 would be set to 0. But there are additional settings for the front and rear lights, so that you can have the front ones on when you press the "light" key but only when going forwards (by setting CV52 to 128 instead of 0) and the rear ones on only when going backwards (by setting CV53 to 64 instead of 0).
The setting for what key controls function output 1 (as I said usually smoke generator) is up to you. If there is nothing connected to the socket or pins then it doesn't matter, you could leave it as 1 (CV51 = 1). If there is a smoke generator connected then whatever key you choose will turn that on and off.
Earlier someone suggested you increased the voltage for the function output F1 (CV49) and lights (front and rear set by CV50) to max (32 = track voltage). I would put those back to 5 or 6 and use a voltmeter to measure what voltage is generated for the lights and function output F1 and then adjust accordingly. If you have a 5v smoke generator attached to function output F1 and you put full voltage through it with no smoke fluid in it will glow red hot then fail.
Sorry this is so long, I wish I had more time to make it shorter and more concise, but I hope it helps.
Speed forwards and backwards correct so the only bit missing is the lights and I know they work as they work in old school mode with the dip switches flipped and they did work before I changed the Loco address so I just need to find what value and what CV to get them working again correctly.
