In both gas and diesel Cruisers, check the alternator for excessive play. A brand new onw is worth a small fortune. Rebuilt 12V Diesel alternators are difficult to find and 24V ones are virtually impossible. If a diesel alternator with a vacuum pump on the back shows any signs of oil leakage, it's probably shot.
If you find that there are accessories (radio etc. attached to only one battery of a 24V Diesel, you can expect to replace the battery shortly. Drawing 12V off one of the battery loads them unequally leading to undercharging of one and overcharging of the other.
In 1974 and up 40 Series, a dead bulb, bad ground, or wiring problem in a turn signal will result in the indicator light in the dash sticking "on"
In 60 and later Series the same type of problem will show up as the indicator light flashing "double time"