John Deere 790 - where is the fusible link? A little help!

[kebo]

My JD 790 is totally dead, it does nothing when I turn the key. Three weeks ago, it was running just fine and I cut grass for two hours, then I parked it. Last weekend I went to crank it up and for about 1 second I barely got a red light on, and a faint click of the starter solenoid. Then NOTHING. I charged the battery (in the tractor) at full charge for 3 hrs, turned the key and NOTHING. So I then hooked the charger back up to the battery (still in the tractor) to see if the charger would even light up the red indicator light, or move the gauges, and turned the key... NOTHING.

After raising the hood and taking the side covers off, I see the fan belt is loose as a goose. I suspect it was barely turning the alternator so it was probably running the battery down. Looking at the wiring diagram, I see there is a fusible link in between the starter and the ignition key switch. I suspect it is now open as it gets no lights, gauges, or sounds when I turn the key to ON, and then turn it to CRANK. NOTHING!!! I've already called my JD dealer and the link is an $8 part, so they have one on order for me and it should be in tomorrow.

Unfortunately my tractor is about 60 miles from me, but I will be up there Saturday morning to look at it again. I will be taking my DVM to make some voltage checks on it. If anyone here can tell me exactly where the link is, I would appreciate it. I think I may have to remove a panel or two from around the steering column? TIA.

 

[beenthere]

kebo
Searched my service tech manual which includes the 790 new version.. found the following schematic.. indicates the wire color which may help locate it. On white/red wire between the starter and the key switch. Hope that fits with your replacement link and is some help.

 

[kennyd]

I suspect the battery is shorted, check the voltage at rest and while trying to start it.

 

[Zebrafive]

kebo
Searched my service tech manual which includes the 790 new version.. found the following schematic.. indicates the wire color which may help locate it. On white/red wire between the starter and the key switch. Hope that fits with your replacement link and is some help.

From the drawing,

Before replacing the fusible link, I would check the continuity of the wiring from the battery + to the "B" wire at the ignition switch. Or check for voltage at the "B" wire at the ignition switch.

 

[jd110]

Nobody has mentioned battery cables, so I will. Be sure to clean all connections at battery and at the ground cable connection on the frame. In my experience, 90% of the time when there is a sudden loss of all electrical power, a bad connection or a bad battery cable is the culprit. The fusible link is just as the diagram that beenthere posted. It is right by the starter about 3 inches from the battery cable connection.

 

[kebo]

kebo
Searched my service tech manual which includes the 790 new version.. found the following schematic.. indicates the wire color which may help locate it. On white/red wire between the starter and the key switch. Hope that fits with your replacement link and is some help.

Thanks, this helps. My dealer called this morning and said the part (fusible link) came in, the link itself is red wire. They also printed off a copy of the wiring diagram similar to what you had attached. He gave me two versions of it, one for the 28hp 790's and one for the 30hp 790's, which is the one I have. Thanks again!

 

[kebo]

I suspect the battery is shorted, check the voltage at rest and while trying to start it.

That's one thing I had not considered, but I suppose that could be the problem. However, when I had the charger hooked up to it, it seem to take a charge as normal. Starting out at about 4 amps and then ramping down to about 1 amp after 3 hours. Would a shorted cell behave like that??

I will be taking my Fluke meter with me and the first thing I will do is check the battery voltage. If that's ok, then I'll start tracing it down to see if I can find where the open is. The next thing I will do is to tighten the fan belt on it! I think that is what started the whole problem anyway. Will post back what I learn Saturday. Thanks!

 

[kebo]

Nobody has mentioned battery cables, so I will. Be sure to clean all connections at battery and at the ground cable connection on the frame. In my experience, 90% of the time when there is a sudden loss of all electrical power, a bad connection or a bad battery cable is the culprit. The fusible link is just as the diagram that beenthere posted. It is right by the starter about 3 inches from the battery cable connection.

That's a possibility, but recall that I mentioned that the fan belt is SLOPPY loose! I can rotate it by hand, so I don't think the alternator was charging the battery as it normally would, which I believe is what precipitated the problem. If the belt was completely tight, then I would agree with you and check all the connections. If the fusible link checks out, then I will start looking all the cables and connetions. Thanks!

 

[kuboman]

I have had more than one battery show good voltage and take a charge but completely short out as any draw is applied. I'm betting battery or cables.

 

[texasranger556]

+1 for checking battery cables and especially the battery ground wire at the chassis end. I had a Kubota act similarly and it ended up being the ground cable, clean and re-tighten started right up.