Odd PTO issue - seat safety switch maybe?

[OutdoorEnvy 1,522]

So my 1985 312-8 I recently got has one odd issue.  When I start to mow and engage the PTO lever it immediately kills the engine, just like a safety switch would.  What's odd is if I immediately disengage the PTO the engine comes back and stays running.  If I cycle the PTO like 4-5 times real fast it will be fine and stay on and I can go ahead and mow.  Engine sounds great, I have it at full throttle when I engage the blades, etc.  Once it's going it is perfect.  It's only at the beginning that this happens.  I believe it's either the seat safety switch or if there is a blade engagement switch I'm not sure as I haven't checked.  Can these switches be saved by cleaning terminals, etc?  Or is it better to just replace them?  I've messed with them on newer stuff and do have a multimeter and know how to test them.  Just more wondering if the older switches are better and worth trying to fix or not.  Or if I'm on the wrong track here and it's something else.  Thanks for your help!   

[gwest_ca-(File Mod) 11,046]

The wiring is also odd. By all means clean up all the connections.

When the pto is OFF the pto switch powers the ignition switch which powers the ignition.

When the pto is ON the seat switch powers the ignition switch which powers the ignition so operator must be in the seat.

 

It may be that the seat switch is barely closing so ignition switch loses power.

Click on the picture in the link to view the diagram.

 

Garry

[OutdoorEnvy 1,522]

Thanks Gary.  That helps a lot.  Probably wouldn't hurt to clean the key switch terminals too. 

Edited May 11, 2021 by OutdoorEnvy

[peter lena 8,634]

@OutdoorEnvy, agree with garry above, on cleaning connections , adding dielectric grease to increase conductivity , stop corrosion . another thing that's quite common  on multiple connections is the cracking  / splitting of the plastic multiple connector . those are often the main cause of erratic issues. found  OREGON  , chain saw parts , has those multiple connectors , also a good time to reroute tight chafing wiring areas . had similar wiring issues , also increased engine / frame grounding to battery ground rail , no issues since , pete

[peter lena 8,634]

@OutdoorEnvy, here is the oregon related connection site ,https://www.google.com/search?q=oregon+wire+connectors&sxsrf=ALeKk03QM6UPoovco0TmTK9VCW7cBsW_QA%3A1620745136613&source=hp&ei=sJuaYO60IpGg5NoPkpaugAo&iflsig=AINFCbYAAAAAYJqpwC12MM1SYmw4oBNpDMlIYZDtyODs&oq=oregon+wire+conn&gs_lcp=Cgdnd3Mtd2l6EAEYADIFCCEQoAEyBQghEKABOgcIIxDqAhAnOgQIIxAnOgsILhCxAxDHARCjAjoICC4QxwEQowI6BQgAELEDOggIABCxAxCDAToCCAA6BQguELEDOggILhDHARCvAToICC4QsQMQkwI6AgguOgsILhCxAxDHARCvAToFCAAQyQM6CwguEMcBEK8BEJMCOgYIABAWEB5Q6EZY1IUBYM2-AWgBcAB4AIABa4gB5wuSAQQxMC42mAEAoAEBqgEHZ3dzLXdperABCg&sclient=gws-wiz  pete

[OutdoorEnvy 1,522]

Just an update.  This issue was at the seat safety switch but the switch was fine.  Confirmed with a continuity test.  Issue was the rust and dirt build up at the terminals.  I cleaned the prongs on the switch with sand paper and the connectors had heat shrink tubing on them.  And while this seems like a good idea they were full of rust and dirt to the point I gave up trying to clean them and just put on two new connectors.  Did use red ones though!  Fixed the issue!  Stays on once engaged now the first time.  

 

 

 

[Jeff-C175 7,202]

28 minutes ago, OutdoorEnvy said:

the switch was fine

 

Obviously someone was in there in the past.  The zip tie looks old so I don't think you took the switch apart.  

 

Ditto the suggestions for dielectric grease.  "I put that 5h1t on everything"