first changed the alternator (stator and cover) from (charging bike) there was a black pickup held in with two screws, two wires and another four wires to the generator. came across problems with this before, think bike would start when it was warm, problems when cold! (DIFFERENT BIKE)
well this made no difference, battery still dropped when headlight was switched on, from 13.5v to 12 and under!.
Then tried the regulator rectifier, which was really hot to touch big difference. No voltage drop! success

held at 13.5V with light, horn, indicators!!!
~Then fitted the original stator cover, to cancel out this, so the bikes own, coil was and stator was fine!
Anyone any ideas where I can get a reg rectifier, prefared New, and will any type fit> ie FZR600.
The part number is 3tj -00 SH629-12 (0.2.1) this is from a 1992 UK spec FZR 400 RRSP
this has fins in it, (for cooling) held on with two bolts and has a 4 pin plug slot
The Jap import number is 47X - A1 SH569-12 (9.4.2) 1995 jap spec 400 RRSP
flat type, held on with two bolts, also 4 pin slot
althought different, it bolted perfectly and seems to work fine!
also can the pickup coil inside the casing be got new, held in with two screws, and two wires head wrapped, and about 1ft of wire, two spade connector into loom. it looks like its on its last legs
Cant wait to get a reliable bike back!!