Appreciating already the collective wisdom and experience that resides in ACMOC!

As noted in a previous post, I am a newbie with a 1968 (maybe 1967 according to S/N, 59H498) 12F grader, affectionately known as Hanna. Starting was not a problem until I (foolishly, I now know) followed the instructions on the plate in the cab--leaving Heat on for a full two minutes before trying to crank. When I then went to crank, nothing happened. This led to all kinds of sleuthing--determining that the batteries were fully charged, that no fuses had blown and that the manual breaker switch had not tripped.

If I turned the master power switch off for a bit, turning the start switch to Heat would produce some rattling in the solenoid relay. I replaced the solenoid relay thinking it might be the problem. But no go. (See attached photos to see all that I am referencing.)

I have wondered about the breaker switch, but if I bridge the two leads, it makes no difference.

However, if I connect the hot lead on the start switch directly to the positive battery terminal, everything works fine--the glow plugs glow (at least enough of them to start the engine--I think one or two might need replacing) and the starter works fine. And, once the old girl is running, I can disconnect the lead between the battery and the start switch and everything seems to be working fine.

Does anyone have any ideas about what I should test and how such testing might be done? Electrical is not my strong suite!

Thanks, guys! I am really wanting to get Hanna restored to her former glory.

Thanks, Neil. I'm working at precisely that. But with a lot of uncertainty. Your advice is helpful.

From what you describe I'd be suspicious of the hot lead (orange wire) going to the solenoid, could be bad pin connector or poor terminal connection. Make sure the glow plug solenoid has a good ground.
Do you have a wiring diagram?

The other end of the hot wire would be where I start looking. That seems to be the missing link. By hooking it directly to the battery you are eliminating what ever is on the other end. Either a bad connection or a bad wire will be found.

Is the master disconnect turned on?

Mr Magnet and Neil bring up very good suggestions...i feel electrical is the least understood area of expertise of most mechanics...(me included)

-i have seen way too many (bizarre) problems and gremlins created by a poor ground....i think OM is onto something...

-remove and test each component if possible...
-sometimes its just a process of elimination...it takes time
-clean up all connections, contacts, wiring, etc..

Master disconnect is definitely turned on (and off, as appropriate). Working fine.

kittylover123 wrote:

-remove and test each component if possible...
-sometimes its just a process of elimination...it takes time
-clean up all connections, contacts, wiring, etc..

Yep. That's the drill. Hoping to get to it tomorrow for a bit...