My '82 720 Diesel thread

[Slowas720]

I did notice that the glow plug light isn't coming on at all

[wayno]

If you look real close at the light when you turn the key on it may flash briefly, mine did until I figured out the plug came out of the alternator and the fusible link plug was not making contact.

I have had diesel owners come to my house complaining that the engine will not shut down/off, while they turned the key off in front of my house I unplugged and plugged back in that injection pump controller plug, the engine shut down and started properly after that, I call it cycling the plug, the contacts get dirty and it doesn't work right, like the 4 way switch on the 720 steering column, shit don't work right when that switch gets dirty, turn signals not working is one of the issues.

 

You need to check all your fusible links, to do this you have to unplug all of them from the harness, none of them can be plugged into the harness to check them, check all 4 of them.

[Slowas720]

Edit ...

 

So I started it, turned the key off and unplugged the round plug and plugged it back in and it did die. I started it again and let it run for a minute and turned the key off and it didn't turn off again.

 

Looks like the arm isn't disengaging with the key, but it does go back after I unplug and plug the plug back in 

[wayno]

Do you have anything to clean the plugs contacts, when you plug it back in it may make a good connection long enough to kill the engine but when fully plugged in/inserted it may not be making contact/a good connection again, they have some electrical spray cleaners just for this, try that.

Do you have a test light, if you don't I would get one, I would connect the light end on the negative side of the battery where you can see it from inside the cab, the clip end needs to go on #4 glow plug, now watch the light as you turn the key on, does it flash or come on for a second or two then go out?

You cannot do test above with a digital meter, you need to see it flash or come on for a second or two, it is supposed to come on and stay on, if it does nothing then I would say maybe a fusible link is bad or a fusible link connection, if you get a flash then I would be looking at the alternator wiring, another thing you need to check is power to the light green wire in the photo below, same as the test with the glow plug power , the light needs to be connected to the negative side of the battery, the clip needs to be connected to the light green wire, when you turn on the ignition does the light come on when connected to that light green wire, if it does not come on then that is why the glow plugs are not being warmed up, if the light does come on but there is no power to the glow plugs then maybe the relay is bad, this stuff is all tied in together, and I am trying to help you over the internet, I don't always test stuff in the proper order, I suppose if it gets to confusing we could do this stuff on the phone in real time, I could be looking at my 720 wiring while you are looking at your wiring, I have test lights, I have this type but they have lights in them not LEDs.