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Discussion Starter · #1 ·
Slowly but surely I'm narrowing down the issues with my 318. You may recall i had the short in the voltage regulator. I have that unhooked and I can get the machine to run fine. Problem I have now is when I go to engage the PTO I blow the 20 amp fuse. Armed with my multimeter, continuity tester and test light I have gotten everything to check out. Key switch, tranny switch, PTO switch (no brake switch on mine) and lastly the light switch all work fine. I have 12volts where I need it and I'm not finding any shorts to ground.

Any ideas? What tests can I perform? One test I'm unsure of is the wire going to the PTO has continuity to ground. Based on my reading of the schematic it should. Am I right?

Ding ding ding.... this occurred to me as I was typing this question. Right not to test I have the battery on the floor and jumper cables going to the battery lugs. This setup does not have the juice to start it. I've had to use my battery charger in 50amp start assist mode to start the tractor. I bet I'm causing my own problems here. When I hit that PTO switch the current draw to the battery is too high because of the 6 feet of jumper cables and the fuse blows. Am I on to something? I left the battery out because each time I put it in something would come loose and I have to undo the battery and tray to see now what was causing the bleeping problem.


Ooops... sorry that got long.
 

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The Magnificent
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I think I'd be careful using that start assist mode. Put the battery back in each time - I know it's a pain.

What 20 amp fuse you talking about Willis? You mean the 15 amp you have overfused?

The PTO continuity to ground needs to be clarified. The PTO winding is a coil, it shoudl offer some resistance on the order of 1 to 2 ohms. A continuity test would show that as having continuity.

Inspect the wiring at the PTO clutch very carefully. It sounds as if you have a short right there (insulation rubbed off).
 

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Discussion Starter · #3 ·
According to the diagram I have there are supposed to be two fused links in my setup. One at 20 amp and the other at 2 amps, they are pink and red wires coming off the 'run' terminal of the starter switch. My 2amp fuse link is gone, its been wired together. The PO had stuck a 15 amp in the 20 amp spot so I think it was actually under fused before, not really a bad thing.

I didn't take a resistance to ground measurement through the clutch. The continuity tester light doesn't glow as bright through that connection so there is definitely some resistance there, just don't know how much.
 

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The Magnificent
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Fused links in a 1985? 1986 and 1987 used glass tube fuses, and I think 1989 or 1990 was the switch to blade type fuses.

Can you send me the link to the schematic you are looking at? I am looking at a hardcopy manual for 1983 and it shows a 2 amp on a pink wire (coming off the ignition switch) and a 15 amp on a yellow wire coming off the front PTO switch.
 

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Discussion Starter · #6 ·
yes, my '85 has glass cylindrical fuses not the blade type.
 

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The Magnificent
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Ok, my old manual is wrong according to the JD parts site. There are 3 wiring harnesses, all of which use a 20 amp on the PTO circuit, and a 2 or 3 amp for the other fuse. The original harness covers the B43G and some of the P218G models. Interesting.

Anyway, so the fuse only blows when the PTO switch is turned on, and not simply when the starter switch is turned on.

It's got to be the blue wire from the PTO switch down to the PTO clutch, or the PTO clutch itself.
 

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Discussion Starter · #9 ·
Sorry for the confusion on the fusible link, I was using the term wrong as I'd forgotten completely about the melting wire stuff. I have always meant to be referencing an inline fuse holder.

The pdf I attached has a 1995 date on it but its been accurate about everything on my tractor so I've used it.

I think my next step is to put the battery back in again. Part of the PIA of putting my battery in is its the wrong size so it has to be wedged in there. Time to correct that problem to I guess.

Thanks for the help (again). Now I wish the pager would stop going off so I can go back to bed.....
 

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Discussion Starter · #11 ·
Back at it this afternoon. I did a resistance check between the lead for the pto and ground and got 4 ohms. This I've read is a good thing and means there is not a short in the clutch.?.?.?

I put the battery back in the tractor and fired it up. Runs good, fuse doesn't blow (although I've only let it run a minute or so before testing the PTO again.) I tested the pto (with no load, mule drive is off) and the fuse blew and the tractor died. I'd be an understatement to say I don't get whats wrong. I've checked many of the wires and have not found any shorts. I guess I keep looking.
:banghead3:crybaby::banghead3:crybaby:
 

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The Magnificent
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4 ohms sounds good.

It is within the realm of possibilities that your PTO switch is internally shorted.

So, disconnect the blue wire down at the PTO and try again. If the fuse blows now, it's most likely the switch.

Or save a fuse, and remove the connector from the PTO switch. turn the switch on, with the tractor off, and ohm between all the terminals of the switch and ground.

While you are doing that, I'm going to go remove the 20 amp fuse from my 318 and see if it will start. It should.

No it shouldn't. It powers the time delay module - what was I thinking).
 

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The Magnificent
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And you absolutely positively swear on your grandmother's grave the blue wire is fine?

Can you rig up a jumper wire with a 20 amp fuse in line?

Connect one end to the blue PTO clutch wire and momentarily touch the other end to the positive battery cable. Does the fuse blow, or does the clutch stay engaged?

This way we can say yes or no on the clutch.

So if we have eliminated the switch, the clutch, and the blue wire, we have to back up toward the time delay module itself.
 

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Discussion Starter · #14 ·
I'm not swearing on anything at this point! But I do believe the blue wire to be fine.

I like the idea of testing the clutch. I assume that test would be done with the motor running? If that's the case I have to wait until tomorrow as I'm down to one fuse.
 

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The engine need not be running to test the clutch like I outlined above.

There is actually a field coil test in the manual which is done similarly with the clutch dismounted. You verify its magnetic field is strong enough to hold a couple of bolts.

You could get all fancy and put your meter into ammeter mode and measure the clutch's actual current draw.
 

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Discussion Starter · #16 ·
SUCCESS!!! (sorta) This evening I did the clutch test with the tractor off and it worked fine... cool. So I put a new fuse in the tractor and started it up. I then flipped the switch on the PTO and vroom, it started spinning no trouble. Hmmm, this wasn't working before so I put the mule drive and deck belt back on. I took the tractor for a spin around the house with the deck off and it ran fine. So I fired up the deck and made a lap around the yard cutting grass.

Here is my theory. The 20 amp fuses I was using before were fast acting. The fuse in there now is a 20 amp of the non fast acting variety.

I added the sorta because after this victory lap cutting grass I started having problems with fuel delivery or the carb. I suspect fuel delivery because I replaced all the fuel lines downstream of the fuel filter.
 

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Interesting. Mine are not slow-blow fuses. Out of curiosity, when you did the PTO test with the tractor off, did you happen to measure current?

On to the fuel problem. Vacuum line to the pump look good? Vacuum leak at the manifold? Check for vacuum leaks with an unlit propane torch.
 

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Discussion Starter · #18 ·
Shazam... The beast is alive! What it took this time was a new fuel filter, which makes sense since I took the tank off and probably stirred up a bunch of junk. So all fuel lines are new, front to back with a new fuel filter in the path too. I blew out the carb with low compressed air and sprayed it down good with carb cleaner. It seems to run fine now.

D-Dogg - I don't know what was causing the pto blow fuse. The clutch drew three amps when I did the test. Not quite 20 amps to blow a 20 amp fuse is it.?.?.? I guess time will tell if the problem is fixed. Thank you for your help.
 
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