My Hero Jerry Jenkinson aka Sojourner posted this step by step diagnosis, maybe it will help? Worked for me.
ice of you to help. Spinning Jim may still need you or who ever is closer for extra hands to do this and repair.
If I were there to witness & diagnose your problem, I can find your problem. For not being there I will try to give you step by step and hope I didn't miss any. Let us know what you're finding. Am not surprise it something else that not been reported.
Here are few steps to diagnoses starter & solenoid & bendix & relay before solenoid & NC (normal close) fuel pressure switch problem: Please use an analog meter only…so you can watch needle to be steady or erratically like a loose connection or dirty relay's points for diagnostic reason. Alligator clip on both test leads to get a good sable connection. Set meter range at 30 volt DC or the next higher scale.
Before the tests, the batteries should be at 80% or higher state of charge for diagnostic checks but not cranking voltage test unless full state of charge.
I attached a wiring circuit with numbers which label each test points.
A) NC fuel pressure switch:
1) Hook + test lead to #7 and – test lead to #8…while cranking, it should read 0 voltage until it starts.. If it erratically or full battery voltage before engine run…bad pressure switch. Hook up + test lead to #8 and – test lead to chassis GRD… it should read 0 voltage until it starts. If it erratically or full battery voltage before engine run…poor ground wire or connection.
2) If fuel pressure is higher then 8 psi @ cranking speed…checks for restricted return fuel line flow. It will cause the starter to shut down automatically.
B) Starter switch relay before solenoid:
1) Hook up analog meter + test lead to #6 and – test lead to chassis ground…it should be at battery voltage while cranking. Otherwise if it erratically meter movement….bad starter button switch or wire connection.
2) Hookup analog meter to solenoid coil post (#5) (it the same + from battery post) with + lead and – lead to (#4) pressure switch. Watch voltage meter for steady cranking voltage reading while hold down the start switch…if it 0 voltage while cranking is good. If it does erratically while using either front or rear starter switch mean bad wire connection to or in the relay or bad relay points.
Hookup analog volt meter with + test lead to + post (#1) of solenoid and – test lead to starter's + post (#2). Watch for meter goes to 0 voltage while cranking…that is good. But if it erratically…bad connection either in solenoid's contact switch or starter's brushes or wire connection. Take it to repair shop for further testing or replace both solenoid & starter motor with warranties.
D) Bendix Drive:
1) Wrinnninnnn noise (spinning) mean over run clutch is slipping, mean a bad bendix drive.
2) Very loud gear clashing before fully engage…either worn gear's teeth or starter is spinning before fully engage…solenoid connecting link is out of adjustment or worn out. Replace both solenoid & starter motor with warranties.
E) Starter Motor:
Hookup analog or digital volt meter to solenoid's + post (#1) and the – lead to engine's ground. Watch for voltage dropping at the beginning & during cranking. If the voltage is below 18v with a fully charged 24v system and growling noise mean starter bearing is worn out to cause armature to rub on field poles. Replace both solenoid & starter motor with warranties. If no growling noise…check power source for weak & “hot” (high resistance) connection of both the + positive & - negative. While cranking with fuel shut off, it should never have more then .5 volt drop between #1 and starting battery's + post. Same way with grounding between engine to battery – post of no more then .5 drop. Under size wire or cable will cause greater voltage drop as well old cable with a few broken strands from too much vibrating and/or corroding.
Whatever you do about getting parts replacement, always take the old one with you to the store same or newer version.
Sojourn for Christ, Jerryhttp://www.busconversions.com/bbs/index.php?action=dlattach;topic=9118.0;attach=9325
Original post http://www.busconversions.com/bbs/index.php?topic=9118.msg90500#msg90500
Hope this helps JIm