Won't some of the time.

[Thomas Moroney 2]

I have a 1995 520H tractor that had some electric work done this past summer. 

The starter, voltage regulator and the ignition switch were replaced.   The problem now is that I often have to take a screwdriver across the two terminals on the starter, with the key on, to get it started. I have had it back to the repair shop and they can't find a problem. They tell me it always starts for them.

Does anyone have any idea what I should try next?

[lynnmor 7,354]

The Demystification Guide can be a big help, here it the simplified diagram of your starting circuit:

 

 

As you can see the three safety switches need to pass current.  I would start by checking for 12 volts at the light blue wire on the PTO switch while sitting on the seat and trying the ignition switch.  Work up or downstream depending on the results of the test.

[953 nut 55,815]

Your Neutral Safety Switch may be a bit touchy, while seated with your foot on the brake and the key held in the START position jiggle your direction control lever and see if it has a sweet spot.

[squonk 41,345]

Check the Molex 9 pin connector by the fuse box. Take it apart and look at the terminals..Dirt, high amperage and muffler heat char them. 

[Wayne0 515]

I've had problems with the seat switch as well. Bad connection.

[Handy Don 12,467]

13 hours ago, Thomas Moroney said:

Does anyone have any idea what I should try next?

You mean besides a smarter mechanic? 😬

 

@lynnmor, got you covered!

[squonk 41,345]

That wiring diagram doesn't show where the wires pass thru the 9 pin connection which I think is a load of crap

[Handy Don 12,467]

20 minutes ago, squonk said:

That wiring diagram doesn't show where the wires pass thru the 9 pin connection which I think is a load of crap

The demystification guide does not, but the wiring diagram in the OM does. 

I get that might be hard for some, but for most of us it is not difficult to mark up the demystification diagram with the additional info.

[Wayne0 515]

That 9 pin is the Devils tool!

[Handy Don 12,467]

2 hours ago, Wayne0 said:

That 9 pin is the Devils tool!

I’m of two minds on them.

Yes, for tractors exposed to the elements for 30+ years, especially those used in challenging environments and rarely if ever cleaned, they can fail. Yet many, maybe even most, including the one my P218, are still in perfectly fine working condition.

And also yes, having that engine connector on the engine from Onan probably saved thousands of labor hours during engine testing at the Onan factory and during assembly at the WH plant and the many other assembly plants for products that used those engines. Costs REALLY mattered to the WH engineers and keeping them down allowed them to stay in business.

And finally yes, while it is a nuisance to debug and/or replace, it can be replaced with modest cost and effort using still-available parts and tools.

[lynnmor 7,354]

4 hours ago, squonk said:

That wiring diagram doesn't show where the wires pass thru the 9 pin connection which I think is a load of crap

Page 7-98 in the Demystification Guide has the complete diagram, here is a portion of it showing the 9 pin connection.

 

[squonk 41,345]

That's wonderful,  but the connector should be referenced in the other diagram as well.

[Handy Don 12,467]

19 hours ago, squonk said:

That's wonderful,  but the connector should be referenced in the other diagram as well.

Gee whiz, this is something we all got for free!

You could go through the guide and create modified versions that show the connector and assemble into a supplemental version of the guide! 

 

I’m sure @gwest_ca would be happy to upload it.

Edited February 3 by Handy Don

[squonk 41,345]

Someone who is unfamiliar and not proficient with working on electrical circuits would benefit greatly if all the info was in the diagram. I use wiring diagrams all the time and know about the 9 pin connector. I have spent a lot of time diagnosing a problem, quite often under a gun (walk in freezer thawing for example) where info and changes are left out of the diagram.  The first diagram posted is a nice shortcut to the starting circuit. But it sure would be nice if that connector was shown so the person working on it knew it was there. Whoever wrote the guide did a great thing, but it could have been even better. 

 

The main thing with me  is  the 9 pin connector was the most likely problem  (At least on all of the Onans I worked on with starting issues were)  and it's not even on the diagram posted