Weird electrical issue

[DWW]

All I know is that until I don’t clear the fault and achieve full battery voltage on the brake light circuit, there is no point being too philosophical about those issues….

[johnetype]

1/ The relationship between current and voltage for a LED is not a straight line. LEDs have to be operated in a current controlled environment. The voltage is not limited by the alternator. In a system with the original 4TR regulator the field current is set to maximum as soon as you turn on the ignition key which means that as the engine RPM rises the alternator voltage will rise uncontrollably until the 4TR regulator catches up leading to a voltage spike. As for cars with a generator and mechanical regulator, the voltage can be all over the place.

2/ The "regulated supply" appears to be 12 volts shared across 6 LEDs in series. There's nothing to limit the current flowing or to make the subsequent voltage across the LEDs equal. If one LED fails, they all go out.

3/ Thank goodness for that.

LEDs are very intolerant of over current situations. All the ones you list such as battery boiling or coil burn out take minutes or hours of over voltage, a LED will die in milliseconds.

[DWW]

I have an after market alternator, the 4TR regulator is out of the game as the alternator has its own regulator.

[DWW]

All fixed now with a mechanical brake light switch installed. Marek's led reverse/brake light works a treat. Thanks for all the help

Photos, for those interested, to follow tomorrow.

[hovrlovr]

Re third brake
light for an OTS... buy the third brake light from an XK8 at an auto breaker, easy connectionto the brake light hot wire in the trunk (boot)... It also places the 3rd light up higher in line of sight. I also added a flasher unit so it flashed first then went solid..... 66 OTS
thanks, and good luck....
Don