Sort your electrics with the following tests.
Equipment: digital multimeter, for most tests set in DC Volts 0-20V range
(if not auto-ranging)
When measuring voltage on a good wire from one given point to another, the good wire will conduct all the voltage
leaving little to be measured. The gold standard for this sort of test is about .2V loss. With a measurement less than that
you can be certain that the wire is good, and well connected. More that .2V, suspect corrosion, frays, loose connections
or some other form of bad wiring.
.2 Volts = 200 milivolts
Tests:
Alternator to Solenoid
(often uses as a buss for fuse box and for unfused accessories, too) Use a digital multimeter selected to volts. If not auto-ranging, choose 20vdc scale.
Put red lead on the solenoid, black lead on alternator. Should read less than .2 v
If not, clean and/or replace wire.
Battery to solenoid.
Same meter setting, measure from red post on battery to battery post of solenoid. Pull coil power wire. Crank for a couple seconds. Again, if meter shows greater than .2 volts, bad connection or wire.
Charge voltage at battery
Connect red lead to red post of battery, black to neg post
turn all accessories off
start engine, idle
meter should read 13.2 - 14.5 vdc
if less, alternator is not putting out correct voltage, slipping belt, loose connection
Alternator charge, loaded
CRITICAL TEST
Connect leads to battery -- red to plus, black to neg
Start car, let idle
Read voltage as in last test
Turn on lights
Voltage should be same plus/minus .2volts
If voltage drops more than .5 volts, rev engine to 1500rpm and hold steady
If voltage increases to no-load reading, alternator is OK
If not, check connections, belt etc.
Turn meter function to AC volts. Should read less than .5 volt AC -- if over, bad alternator (alternator diodes leaking)
Ground test
Meter to DC volts 0-20 range
Red lead to alternator body, not terminal (fin, nut, etc.)
Black lead to a body, not engine, ground point
Start engine
Turn on lights
If meter shows more than (you guessed it) .2 vdc, you have a ground strap problem