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now most of the time its not charging but occasionally it starts working (i can tell as i have a volt meterin the car) and when its not working the power steering goes and the speedo goes.
Was it a new alternator you fitted?? I changed the alternator and the problem didn't go away. Have you got the battery light on the dash when you turn the ignition on? It should be there until the engine is started (Mine isn't until I wriggle the plug on the alternator). Im going to chop it off tonight, take it apart, clean it out and then re-solder the wires back to it.
Turns out the brushes were worn on the alternator so had a recon one fitted. New battery fitted as well and now, touch wood, not had a single problem since. 
- winners of JAE best overall club stand 2010, 2013, 2014 & 2017!1994 GT-S T-Bar 397bhp with NOS *sold*2016 Porsche Cayman 981GTS 347bhp Flat Six It turned out to be the wiring loom underneath the intake manifold. Some of the wires which had been joined using crimps by Toyota had crumbled to nothing leaving an intermittent connection. 
/ sheth, had this on my REV 1 Mr2 turbo./ movment in the wires intermittanly connect causing it to charge and then disconnect so it does not charge while driving and so on./ current to work the same as most of the other high power electrical equipment like ABS.