Originally Posted by bumpstart
in my first response it is assumed he already has wired that white/black L wire up as there is no change there between s4 and s5
if you hook up the black /white to top of the tee and nothing else the alt will still turn on first time you lift revs to 1500 rpm
this is how most do it in older RX changing form external reg to internal reg 12at/s4 alt
else there is complications of adding a latching relay to get the signal polarity correct at the light
It's self exciting itself with the fifteen hundred rev. In normal stock car operation the only current to the field of the alt (initially) is thru the L wire being fed by the coil in the alt relay (inside the CPU on a series four car).
The top wire should be feeding the regulator/transistors but not outputting to the field until the alt is actually rotationg and the diode trio is now putting out. The diode trio feeds the field from then on.
The alt relay in the CPU then relaxes 'cause the voltage on each side of the alt relay coil is the same.
Three cheers for Casey Stoner the top MOTOGP rider (AUS).