1990 312-8 Seat Safety Switch

["Manic-Mechanic" 1,253]

I have been running the tractor with the switch unplugged so never bothered to investigate it.

However, recently had the area apart and just made sure the tail lights worked, never gave thought to the seat switch.

come to find out the panel light should be on with the switch unplugged.

I plug the switch in and the panel light stays on regardless? Very simple circuit but something isn’t quite right, in fact might even be backwards! lol!

There are so many schematics for the 312-8 based on DOM.

I have been going back and forth with Gary on this and time to just have at it this morning.

The switch functions correctly. Now it does stand to reason the panel light should be on with the switch unplugged, however, this light is not. It’s the other way round.

Perhaps the ground and one of the green wires is reversed while landing the tail light wires?

We shall see here this morning........Here is a drawing from another post on this circuit, (Gary).

The schematic from the manual to see of my tail lights some how got involved! Lol!

sub

 

 

"I hope to be able and do this without removing the rear fender"

 

Edited March 17, 2021 by oldman

["Manic-Mechanic" 1,253]

Now, I’m really confused!

The tail lights are correct,

+ from light green single wire off light switch.

- from lights to black, chassis ground)

 

ignition on, seat switch plugged in engage switch get light.

 

Ignition on, seat switch unplugged, parking light on, depress brake lock, seat light joins parking brake light.

 

Ignition on, seat switch engaged, plugged in, parking light on.

 

Ignition on, seat switch plugged in, seat up, no light

  

 

I am now thinking the parking brake lock lever switch may be wired backwards?

The Clutch and or PTO switches both work as they should.

I am at a loss otherwise.

Edited March 17, 2021 by oldman

[pfrederi 18,566]

Unplug the darn warning light circuit board... 

["Manic-Mechanic" 1,253]

About ready to do just that! Seems the parking brake switch turns on the seat light when I set the brake!

Although, the brake light stays on as if the brake switch is unplugged, but it isn’t.

The two plugs in the harness cannot get mixed up as the seat switch plug is wired a foot longer and has the tail light + as well  coming out of the harness!

[Handy Don 13,689]

Sorry, but the different combinations are losing me. I go back to "what is it supposed to do" and the wiring diagrams.

 

Seat lamp should go on in a situation where the tractor wants you to be seated and you aren't -- i.e. PTO engaged. Not sure, but on a magneto engine doesn't this state also ground the mag output to stop the motor?

 

Parking lamp should just tell you state of the brake. (brake set, engine in Run)

 

That the wiring to these two switches has been swapped makes sense to me.

Edited March 17, 2021 by Handy Don

["Manic-Mechanic" 1,253]

Yea,

I tested the whole plug and all the switches, all grounds are Black and Orange will beep to ground as well

I went to my jumper ground to green on the seat switch, that the parking light goes out instead of shining full time!

Then when I use park the seat light comes on and functions as a parking 

so , swap the two names on the decal!

(The brake an seat lights both out while running) this way, otherwise brake light on full time in run

Just be glad it charges and runs perfect.

Not gonna track down a new board or anything at this time.

 

Edited March 17, 2021 by oldman

[clueless 3,181]

2 hours ago, pfrederi said:

Unplug the darn warning light circuit board... 

Always found it funny that the warning light panel was the first to quit working way before any of the switches did .

["Manic-Mechanic" 1,253]

If you unplug it the spark goes bye bye!

So,.....maybe another board and seat switch, switch & plug matter of fact.

Edited March 17, 2021 by oldman

["Manic-Mechanic" 1,253]

5 hours ago, clueless said:

Always found it funny that the warning light panel was the first to quit working way before any of the switches did .

You know this panel never worked 100% but I have the parking brake, clutch or neutral safety, oil. and pto- all will light up as needed. So no seat switch. I don't know that panel is shorted or the circuit still has some other issues? The seat switch, (in my humble opinion) is marginally engineered at best and designed to fail mechanically!

Could track down the parts, but right now the clock is keeping good time.......

Edited March 17, 2021 by oldman

["Manic-Mechanic" 1,253]

I removed the pc board & harness

tested out the resistance,

direction of the diodes

all lamps work

made a proper “jumper”

 

see if this makes a difference 

["Manic-Mechanic" 1,253]

9 hours ago, Handy Don said:

Sorry, but the different combinations are losing me. I go back to "what is it supposed to do" and the wiring diagrams.

 

Seat lamp should go on in a situation where the tractor wants you to be seated and you aren't -- i.e. PTO engaged. Not sure, but on a magneto engine doesn't this state also ground the mag output to stop the motor?

 

Parking lamp should just tell you state of the brake. (brake set, engine in Run)

 

That the wiring to these two switches has been swapped makes sense to me.

I completely traced the circuit back to the pc board. Cleaned and totally tested the circuitry.

There maybe a significant improvement.

["Manic-Mechanic" 1,253]

Well, 

      Installed the board and it insists the seat is the brake! So, looking at the drawing the light green/white control both seat/brake to the plug end of the harness.

So the two wires could be swapped in the plug. As the brake light is on full time, (regardless of the position of the lever), it is responding like a seat switch. Then, as my brake lever is set, the seat light comes on!

 

[biged77 113]

 

OK I have a 1989 414-8 and the wiring diagram looks the same as yours except no connector for the PC board (wires are run direct to the board).

 

Here's what I get:

1.  Ignition in run, seat switch not engaged (operator not on seat) - Seat Light ON

2.  Ignition in run, seat switch engaged (operator on seat) - Seat light OFF

3.  Ignition in run, seat switch unplugged - Seat light ON

 

The above is opposite of what you got.  Good chance your PC board is bad. Either that or the wiring is really messed up but you already checked that. I don't think swapping 2 wires will help.

 

You also said if you disconnect the connector to the PC board you get no spark.  I thought the test lights were to just to show the position of the switches.  Could be the defective PC board is somehow shorting out the magneto although I'm not sure how this could happen.  If I had a connector like you I would disconnect it but like said my wires are run direct.  Maybe someone else can try this.

 

["Manic-Mechanic" 1,253]

 the black wire on the beginning of the harness, next to the orange magneto wire, doesn't test to ground on the battery negative 

the board requires two grounds. Ignition ground and ground at the Oil Sensor, etc

 

So yes, there is an issue with the harness below the pc board, perhaps down in the loom of the harness towards the solenoid?

Edited March 18, 2021 by oldman

[gwest_ca-(File Mod) 11,393]

If you look at the diagram at the start of this thread it looks like #1 ground is connected to #12 ground. This may be accomplished by the circuit board when it is plugged in. One would have to study the copper PC board traces to see if that is so.

 

Garry

["Manic-Mechanic" 1,253]

I believe it’s time to send the board of to be tested now that the harness has been ruled out. A-Z can test them.

 

3703.pdf

Edited March 19, 2021 by oldman

["Manic-Mechanic" 1,253]

I have a parking brake light on the parking brake console and that’s it for now!