Electrical Gurus: Why is there a small red wire from B+ on the alternator to fuse #24
 

Looking at the schematic in the Bentley SC Manual 970-02-03, it shows:
Large red wire to starter,
Small red wire to fuse 24 (And 23) in the engine comp.
Blue wire to idiot light,
Brown is ground.

Why is the alternator supplying power directly to these 25A fuses for the Rear Window Defogger Relay and
Heater Ventilator Relay ???

Why is the power for these relays not coming from the fuse panel in the front?? :confused:

The power for WUR and AAR is coming from the front, why not for these relays ?? Too high Amp-draw?

For high-demand accessories that happen to be located in the rear of the car, like the rear window, it makes sense to run current directly from the alternator, through the fuse, and then to the accessory.

Put another way, if the factory did what you propose, all the current would have to run from the alternator to the starter, through the fat black cable to the battery, out of the battery to the fuse box, out of the fuse box back to the rear of the car, in and out of the relay and then to the window.

That's a long trip for the current to take, with resulting voltage drop, greater weight and cost for the manufacturer.

The current for the WUR and AAR is way, way less than 25 Amps, and it needs to be switched from the front of the car anyway, no relay.

Good luck!

Thanks John, that makes sense.
I see now that the Defogger switch in the dash controls the rear relay but the actual power for the defogger comes from the alternator through fuse 24.