hi all again!, been busy getting car finished all day and at the end of the day when i was about to go home my mate told me my sidelights were switching on when i depress the brake pedal, it obviously dont happen atall when you put the sidelights on, i didnt have the problem before but i did change my brake light and rear fog light bulbs for working ones (passenger side), plus i did put a new passenger side brake light cluster in too since my other one was all faded and dark, just hope someone has had this problem before as wiring isnt my strengths ,
Its the earth bar in the rear clusters, a really common one and the bulbs are finding a path to earth through another bulb. You'll need to clean all the holders and the earth bar.
That should hold it for a good while if you can get everything clean.
Chris (Chris_C) has done a mod to his car where he solders a direct earth to each holder, which very neatly prevents the problem occuring but he'll fill you in when he comes on later.
Problems with lights is usually to do with an earthing problem. Someone posted a tutorial here on how to make sure the lights are well earthed involving solding a short piece of wire. Have a search.
As you've "put a new passenger side brake light cluster in" I'd suspect that. Have a look for currosion and clean any up
Yup, you are all right guys, Kar did this when I bought it. I said I wanted an MOT on it before I picked it up, and it had failed as the front sidelights came on when the brake pedal was pushed. Dude managed to wait an hour or two, passed it, and I fixed it when I got home.
Nate, have a nosey at the pictures here http://www.ecs.soton.ac.uk/~clc202/earthlight/index.htm
Black wire between the edge of the holder and then crimp a ring (and some solder if you use an uninsulated one, which you can as it's an earth). To solder that wire, use a useful sized iron (at least 25W) so you can get the heat into it quick enough without melting the plastic. Might be worth pulling a scrappy one so you don't screw the job, and have a less legal car
little update, i was able to stop the brake/sidelight problem but as you stop one problem another occurs, i didnt do the earth brake light method as i thought ive stopped it, i keep getting somewhere but now ive got to the point where my rear foglamps are on and only driver's side sidelight is on when you switch it onto sidelights , makes no difference switching it onto full beam (the 2 on the light switch)i can say all bulbs are working as ive replaced half of them to be safe .
sorted , partly my fault for not having keys turned in ignition preventing headlights working without me realising , but there was still a light always playing with me which was driver's side brake light and now thats sorted as someone who owned car before screwed wire to the bracket on the cluster making a large split in wire, bend wire then electric tape it and presto it works again, only if i thought of takin drivers side cluster off sooner then i would have noticed , time to fill the car up and take it for a spin
and at the end of the day when i was about to go home my mate told me my sidelights were switching on when i depress the brake pedal, it obviously dont happen atall when you put the sidelights on, i didnt have the problem before but i did change my brake light and rear fog light bulbs for working ones (passenger side), plus i did put a new passenger side brake light cluster in too since my other one was all faded and dark, just hope someone has had this problem before as wiring isnt my strengths 
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, makes no difference switching it onto full beam (the 2 on the light switch)i can say all bulbs are working as ive replaced half of them to be safe 
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, but there was still a light always playing with me which was driver's side brake light and now thats sorted as someone who owned car before screwed wire to the bracket on the cluster making a large split in wire, bend wire then electric tape it and presto it works again, only if i thought of takin drivers side cluster off sooner then i would have noticed