Reverse lights and speedo stopped working?

Hello again, the other day I was fitting a rear led work light to my new disco 1 300tdi, I ran one wire from a permanent live via a dash mounted switch and back to the light, one spliced into the reverse light wire behind the rear drivers side cluster and spliced the earth into the earth wire on the rear cluster. all seemed to be working but the reverse lights wouldn't work so I thought maybe I should leave it and use a relay etc and disconnected the wire that fed from the reverse circuit to the led only to then find that they still didn't work and my speedo had also stopped working?
I have also noticed the fuel gauge goes up and down as I ascend and descend hills which it didn't do before? I have checked all fuses under the steering drivers dash and they all look fine are there any hidden fuses or relays that could be buggered?
thanks.

Oh dear did you disconnect the battery before you touched the wiring?.
I don't understand that after installing a permanent live to the work lamp why you are touching the reverse lights.

All the fuses and relays are hidden, relays are behind the front foot-well kick panels and fuses are in the main fuse box which u know about or in the engine bay fuse box.

Using a relay depends on the current loading and size of cable what is the load of an LED work lamp , not a lot I would think..

I don't have time to look a my Haynes wiring diagrams but when multiple circuits fail it could be a fuseable link blown or an iffy earth connection, suggest you go over the work you did checking any existing wiring and connections you interfered with including the rear earth points.

I was wanting the rear light to come on when I put the car in reverse because I have to reverse out onto a busy single track road at night.
I had the battery disconnected, ive checked all the fuses behind the drivers side panel, are there ones on the passenger side? ive checked the engine fuses they are fine. I do think the alternator is playing up and I have a replacement but don't think that would effect that?
my led light is 10W so draws under 0.9amps so I thought it would be good without a relay?
I have checked all thee connections I made and they all seem good, I disconnected the wire into the reverse circuit when I realised it didn't work so I took it off to see if it fixed it.
One thing I did remember was I unplugged the trailer lighting cable that plugs in behind the rear cluster could this have effected it? I had cut the cable before which caused no problems so was only unplugging the dead cable?

Ok don't see how that can effect the speedo or fuel gauge but it may depend how and where u picked and connected both 12v supplies which u have to the lamp.

I would disconnect what I have done and go back to fault finding on the two items that don't work first of all then return back to the work lamp.