520H Will Not Start

[rmalcook 0]

Hi Guys,

This is a good one. Got done using the machine and went to start it and it will not start. The machine will light the gauge panel and all appears good to go but the starter will not engage.

All safety switches are in good operating condition. I found a bad PTO switch and replaced it and the motion control switch.

I also replaced the battery. I had a back up circuit board, ignition switch, and relay switches. I also had a spare starter, swapped everthing. Nothing has worked. What am I missing that is preventing the starter from engaging? Any and all suggestions are welcome.

Thanks, RAMalcook

[04fxdwgi 0]

Hi Guys,

This is a good one. Got done using the machine and went to start it and it will not start. The machine will light the gauge panel and all appears good to go but the starter will not engage.

All safety switches are in good operating condition. I found a bad PTO switch and replaced it and the motion control switch.

I also replaced the battery. I had a back up circuit board, ignition switch, and relay switches. I also had a spare starter, swapped everthing. Nothing has worked. What am I missing that is preventing the starter from engaging? Any and all suggestions are welcome.

Thanks, RAMalcook

Don't forget the relays..........

Could be any number of things causing this, only troubleshooting will tell.

I've included a drawing of the start circuit if you need it to assist in troulbelshooting the wiring.

Good luck.

Attached Image (Click thumbnail to expand)

[rmalcook 0]

Yeah,

I did swap out the releays and the fuses as well. Thanks for the wiring diagram. I already have a copy and am going to start digging into it today. I was hoping you could narrow it down or actually list the number of things item by item. That would be a big help.

[Wheel Horse Fan 3]

What if you apply power directly to the starter? If that works then just keep working your way back eliminating one things at a time.

What about your seat switch?

[04fxdwgi 0]

Yeah,

I did swap out the releays and the fuses as well. Thanks for the wiring diagram. I already have a copy and am going to start digging into it today. I was hoping you could narrow it down or actually list the number of things item by item. That would be a big help.

Technically speaking, the drawing shows exactly "actually list the number of things item by item" with the addition of the following.

The major culprits in most electrical problems would be:

1. Bad grounding on any or all ground connections

2. The "Molex" connector on the engine harness connecting to the machine

harness, on the left side of the engine, under the battery tray.

[rmalcook 0]

All of your input and suggestions are great. I really appreciate all the ideas. If you will note in my previous post all of the things I checked out. As it turns out, the thing that was causing me my problem is one of the things I thought I ruled out. Very early on I had replaced the fuses. One of the fuses was heavily corroded. In fact I had to use a pliers to pull the 30 amp from the holder. As I did that one of the prongs broke off in the holder. I dug it out with a screw driver and plugged in a new one. Well, the old fuse in all its corrosion spred the holder terminals and the new fuse was not making any contact. Pinch the terminals together insert new fuse and we are up and running. You may want to tuck this in your memory banks for the future. Thanks again.

[Raider12 13]

. One of the fuses was heavily corroded. In fact I had to use a pliers to pull the 30 amp from the holder. As I did that one of the prongs broke off in the

It sure apprears that these 520's have real problem with corrosion in the eclectrical department. I know that my 520 fuse block does not look good at all and is probably the reason the tach doesn't work. You would have thought that a piece of equipment like these would have some kind of water poof fuse box. Glad to hear you have her running agian. Another lesson taught from the school of hard knocks :thumbs2:

[jbkoran 0]

Have similar but very different starting problem with my 1991 520-H.

Turns over fine but does not start. Just purchased machine a while back.

Would run, full throttle while mowing for 4 then 3, 2... minutes, and

now IF it does start, will run less than a minute then will not fire until

several hours later or the next day...

Trouble shooting guide leads to ignition module and/or trigger ring(?).

Relatively new member, first post, sorry if I jumped in improperly but

topic seemed to fit my problem. Any & all advice to further trouble shoot

before I start tearing this down and replacing misc. parts...

Own 10 or 12 Wheel Horses, first w/an Onan.

Thanks in advance for any & all feedback, Bryan K

[Duff 206]

Bryan, your problem sounds more like one of fuel supply. The decreasing run times suggest a progressively clogging fuel filter or line somewhere that now is almost completely plugged but still lets just enough fuel squeeze through to get the machine started. Does the 520 have the little screen thingy inside the fuel tank on top of the shut-off valve?

When you say "fire", do you mean any spark at all or just not igniting anything?

Just my humble take on it...

Duff :thumbs2:

[lawnguy345 0]

Check the white connector used to connect the engine to the chasis harness. The connector becomes hot on those models and tends to cause alot of trouble with wiring connections.

[jbkoran 0]

Thanks for feedback. Plenty of fuel. "Fires up" would describe

both the engine does or did start (haven't tried it for a few weeks)

and after it stalls I've pulled a plug, reconnected plug wire, grounded

and no spark. On the main wire harness, prev. owner bypassed red wire

past the 9 terminal plug with a soldier-less wire connector. I do seem to

remember the white wire on top of the engine looks a bit tanned so to

speak so maybe it is toasted. Will check and post progress if it is the culprit.

Would be a lot better than $250+/- in parts.

Thanks, Bryan

Oh duff, yah 312-8's rank pretty high in my book, got 3, think they're

87, 88 & an 89 all with Mag 12's. Plenty of torque and seem to manage to

have great traction in snow or mud etc. where some of the heavier twins

have more weight on the front tires. Right now I've been running my

GT-1600 that I worked on over the winter. Some people knock em down

because of the Briggs twin and yes I don't think they could have found a

worse shade of gray to paint them with, but it's a runner. It's an 84 with a

2003 42" rear discharge bought new in 2005. :thumbs2:

[92Pony 1]

........................ One of the fuses was heavily corroded. In fact I had to use a pliers to pull the 30 amp from the holder. As I did that one of the prongs broke off in the holder. I dug it out with a screw driver and plugged in a new one. Well, the old fuse in all its corrosion spred the holder terminals and the new fuse was not making any contact. Pinch the terminals together insert new fuse and we are up and running. You may want to tuck this in your memory banks for the future. Thanks again.

I experienced nearly the same thing last year (and that was going to be my suggestion had I gotten in the thread soon enough). I finished tilling the garden and shut 'er down. When I went to restart, nothing. Turned out to be that same (no doubt) 30A fuse.

Wade

[rmalcook 0]

It turns out there is more to the story. Yes, the 30 amp fuse and holder is what I found first. It seems it was a couple of things all bulding up. There was heavy corrosion in the main wire harness connector, a bad pto switch, and an over charging voltage regulator. She's purring like kitten now though. These electrical things just drive me nuts. Mechanical, now that's easy. You can see what's broke and you fix it. Thanks again guys.

[ben 0]

hey had this problem. Try seeing what happens when you take a jumper wire from + terminal on battery to + terminal lead on coil(skinny one) If it fires then you have a fault oil cut out switch if not i have a trouble shooting manual if you have anymore ?'s