Alternator/Charging 200: New Developments

[Vittorio Bares]

Ok - so I'm learning all about charging circuits in automobiles. All my
tests keep pointing to the D+ (term 61) exciter wire. More specifically,
the failure of a diode in the instrument panel.
 
I pulled the instrument panel - which btw, was much easier than I
thought it would be.
 
And guess what - someone had been there before me. They've spliced into
the blue wire going into the instrument cluster. The splice goes to a
diode, and then to the alternator warning light - 'magine that.
 
a) does anyone know how to test a diode? I'm assuming its a resistance
measure?
b) does anyone know what type of diode I'd be looking for if I wanted to
replace it?
 
Thanks !
 
The previous owners also added a wire from the B+ post, that travels
under the car and attaches to the positive side of the battery - I'm
assuming this was to guard against a potential draw from the splice (?).
I didn't see anything significant when for voltage drop. I even took a
booster cable and connected from the B+ directly to the + post on the
battery - with no change.
 
Vittorio -