what is this diode for?!

brian47 said:

The two main characteristics when selecting a diode rectifier are maximum forward current and the maximum blocking DC voltage (sometimes called the peak inverse voltage PIV).
A reasonable diode rectifier for almost all 12 volt motor use, except in the alternator controller and ECU use is the 1N5401 available from Maplins and other sources for about 60p each.
These are 3 Amp devices, plenty of capacity for warning lights and a PIV of 100 volts DC.
View attachment 103720
Diode rectifier Physical drawing and matching circuit orientation.

Click to expand...

Awesome discription,even I managed to understand it !
I'll search out those diodes and replace.
Any suggestions on the other relay I posted?doesn't really seem to do anything when I disconnect it...well not that it found so far!
At the moment I have all electrics working EXCEPT bloody brake lights!!I'm sure the switch has gone so will replace but even so,checking the wires coming out if it I have two greens that are constant live with ign on and the the green/purple .even if I connect directly it lights up all the sidelights! :-/ (This is what was happening before...braking = sidelights and tails on + dash lights) and tail lights on would illuminate brake lights!! Any ideas?can for the life of me find a reason why...have been through all wiring,obviously I'm missing something but what?! Can I just run a new feed from scratch?ie.live to switch them a new cable back to rear lights?bit of a pain but nay be only choice?,

possibly a bad earth somewhere, I got some really strange behaviour with my indicators when I didn't earth the re-electrics properly.
With really bad, neglected electrics its generally simpler and quicker to re-wire than play "chase the earth fault", at least then you know its all working and you understand it all much better after.

Best bet would be to start at the bulb and work your way back.
The tail/brake light has 3 cables, one for sides, one for brakes and one for earth.