Need Help with troubleshooting ignition switch on Murray 12.5 HP

[Rivets]

Ok, we know that the switch is the correct one. Let's go to the first test. Make sure that the fuse is good. You will need to put some weight on the seat to close the seat safety switch. Put the brake/clutch pedal in the down position and apply the parking brake. Raise the deck to the highest positions. If I remember this unit correctly, raising the deck also sets the parking brake. Hope I am right, but is does not matter. Use a test light if you have one for this test. If you don't have one, you can use the multi-meter as a test light by setting it to 20V DC and connecting the ground lead to the negative terminal of the battery. With the key in the start position check for 12+V at the small terminal of the solenoid. If you have 12V your starter should kick in. If not we start back tracking to the key switch. How??? In this order, follow the orange wire back to the PTO switch and test both orange terminals for 12V. Follow the orange wire back to the brake switch and again check for 12V. Follow the orange wire back to terminal #5 (S) of the key switch and check for 12V. Post results and we will continue.

Reynoldston, if you look carefully at the schematic you will see that there is AC current coming from the stator to terminal #3 and leaving terminal #1 going to the lights. This switch has a turnback position to turn on the lights using AC current. This part of the switch has nothing to do with the starting or running of the engine. I think MTD may be getting confused because of this set-up and that is why I am just taking him through the DC systems and forgetting about the AC side at this time.

 

[reynoldston]

Reynoldston, if you look carefully at the schematic you will see that there is AC current coming from the stator to terminal #3 and leaving terminal #1 going to the lights. This switch has a turnback position to turn on the lights using AC current. This part of the switch has nothing to do with the starting or running of the engine. I think MTD may be getting confused because of this set-up and that is why I am just taking him through the DC systems and forgetting about the AC side at this time.



I don't know what in the world AC and DC has to do anything. The alternator or stator puts out the AC. This is what I am saying 12 volt POSTIVE and 12 volt NEGATIVE. NOT AC AND DC. With out the NEGATIVE side you just don't have anything. Not only does the chassis carry NEGATIVE voltage but wires do also. Now if you are working with computer operated systems like on newer motorcycles without a proper ground or NEGATIVE voltage you will do a lot of damage. Now what I am saying is the two switchs PTO and Clutch has both postive and negative going through then. As far as I know a negative turns off the mower engine.

 

[Rivets]

This has nothing to do with this thread, but I feel that I have to answer the last post. Positive and negative voltage only comes into play in an AC (Alternative Current) circuit. In this type of circuit you will have both voltages because the electrical wave will go above and below the median line, caused by the alternate magnetic poles used to produce it. When this type of current goes through a voltage rectifier or regulator it is converted to DC current, the negative voltage is flipped to the positive side of the median line. In a DC circuit you will have only one voltage, positive.

Secondly, if you look at the schematic carefully you will see that the PTO and Clutch switches are really two switches in one. Those connected to the orange wires are NO switches and used only in the starting circuit. Once the engine is started the key is released and the current will start flowing through the switches which are connected by the yellow wires, which are part of the run circuit.

Again I repeat that this reply has nothing to do and does not pertain to this thread.

 

[MTD]

Ok, we know that the switch is the correct one. Let's go to the first test. Make sure that the fuse is good. You will need to put some weight on the seat to close the seat safety switch. Put the brake/clutch pedal in the down position and apply the parking brake. Raise the deck to the highest positions. If I remember this unit correctly, raising the deck also sets the parking brake. Hope I am right, but is does not matter. Use a test light if you have one for this test. If you don't have one, you can use the multi-meter as a test light by setting it to 20V DC and connecting the ground lead to the negative terminal of the battery. With the key in the start position check for 12+V at the small terminal of the solenoid. If you have 12V your starter should kick in. If not we start back tracking to the key switch. How??? In this order, follow the orange wire back to the PTO switch and test both orange terminals for 12V. Follow the orange wire back to the brake switch and again check for 12V. Follow the orange wire back to terminal #5 (S) of the key switch and check for 12V. Post results and we will continue.

I had done this check several times previously and gotten 0 V. Then earlier today I started getting 12V at the solenoid small wire. I tried this again as you asked and noticed the voltage coming and going. Out of curiosity I tried lowering and raising the deck while measuring voltage(and also did a continuity check) and saw same thing - voltages there then not there -and it seemed to be making it worse. Naturally I suspected a loose connection. As I had mentioned before when checking the PTO switch and harness I found what looked like extra wires, taped outside of the factory shrink sleeve of the wiring bundle and tying into the back of the PTO and brake switch harness. One was orange the other was blue which matched nothing on the schematic, and were a smaller gauge wire. They followed the regular wiring down to the brake switch. I checked the PTO switch itself and it's doing what it's supposed to. I put the test leads inside the PTO switch harness and with some jostling I got the the same short, then open readings. I had to call it a day at that point but will have a closer look early tomorrow. Think someone could have been trying to bypass the safety switches? Whatever the case, there's a connection issue in the PTO harness that's causing shorts and opens without the switch involved, which would seem to explain the voltage readings coming and going.

 

[Rivets]

Ok, I understand, am going to shut down also. I would remove those extra wires and going through the tests, just to see what happens. I'll watch for your post tomorrow. Be in and out all day, but will continue to try to help.

 

[Rivets]

MTD, I just found a problem. I have a few others tracking this thread to make sure that we are doing things right. They are contacting me, instead of posting, to keep things from getting to confusing. One of them just pointed out to me that in your post on the key switches, you have the wires going to the B & S terminals reversed. The two red wires need to go to the B terminal, top right and the two orange wires should go to the S terminal, bottom left. That would explain many of the problems. Sorry I gave you the wrong info.

 

[MTD]

MTD, I just found a problem. I have a few others tracking this thread to make sure that we are doing things right. They are contacting me, instead of posting, to keep things from getting to confusing. One of them just pointed out to me that in your post on the key switches, you have the wires going to the B & S terminals reversed. The two red wires need to go to the B terminal, top right and the two orange wires should go to the S terminal, bottom left. That would explain many of the problems. Sorry I gave you the wrong info.

The answer to that would actually be a whole other question of interest although it is related to the post. I'll try to explain as best I can hopefully without creating another fork in the road. The original switch shown in the pic is in fact the reverse of the new switch, in just the ways you describe - B & S terminals reversed. The Lights (L) & Aux (X) are also reversed in the same manner. I have not attempted anything with the new switch. I was hesitant because of the reversed terminals. I think this is a good question of general interest since this was sold to me by a Murray authorized lawn repair service as a factory part replacement for my model . The question being whether those two switches are 100% compatible. But I didn't bring that up because I thought it would complicate things more.

So, to be clear, all of my troubleshooting has been with the original switch which is wired as I described above. And since the mower ran fine before I am assuming that all is well with the way the original switch was wired. The original switch has no clear Letter markings like the new one and even with a magnifying glass I could not find any letters on the old switch, which was kind of aggravating in itself.



Update:

I was able to perform the same continuity and voltage checks I did yesterday and got the same results, which was:

Seat occupied, brake pedal depressed, and deck up (so all safety switches are now closed and ready for START) I checked both voltage and continuity from the ORG wire on the ignition switch to the small ORG solenoid wire. What happens for both is that I'm getting intermittent readings - OPEN to SHORT. I then lowered to deck (blade engage) and same thing. In other words, I could not get the meter to read OPEN (when the deck was lowered) & SHORT (when the deck was up in START position) like it should. I noticed that raising and lowering the deck seemed to aggravate the situation - made it go from OPEN to SHORT on the meter. I also reached my hand in and jostled the PTO switch & harness and it caused the same type behavior. I haven't had time to figure out what those extra wires are for. I'll have to put the mower up on ramps and crawl underneath to get better access. I'll be out for work the next two days and probably won't be able to get to it until Sat or Sun. I went ahead and ordered a new PTO switch assembly in case that's what the problem is.

Does this sound like a switch or harness problem? I checked the physical position of the PTO switch and the deck lever looks like it's making good contact to the button.

 

[Rivets]

Back to square 1, we have to check the switch to see if both of them act the same way. With you multi-meter, connect across the B terminal and the S terminal. Turn the key to the start position. You should have continuity. Releasing the key to the run position, your meter should read infinity. Next connect the meter across the B terminal and the M terminal. Turn the key to the start position. You should have continuity. Releasing the key to the run position, your meter should still read continuity. Do this on both switches, to make sure they are the same. Report back what you find when you get a chance.

One other thing. It gets very confusing when you report back things that I do not request. Remember, that I have to visualize what is happening and when I have to read two or three different things it is very easy to make mistakes and jump to conclusions. That's why I told you my methods are crazy, if I were there to see what was happening this problem would hav been solved by post #10. Sorry but that is the way I am, I warned you.

 

[reynoldston]

In a DC circuit you will have only one voltage, positive.


I will sure disagree with this. I repaired DC electric fork trucks for over 11 years and if you don't know what negative voltage is you will be way over your head fast and it best not go to the chassis. Gas powered equipment just uses the chassis for most of the negative side is the only difference. Has to make a circle back to the battery somehow. Even your house AC current makes this circle all the way back to the power company I think it cycles back and forth 60 times a minute or something like that. I really don't know that much about AC.

 

[MTD]

Result # 1 - for NEW SWITCH

connect across the B terminal and the S terminal.

This gives continuity in START ONLY, then reads open in RUN. Just as you described

Next connect the meter across the B terminal and the M

Turn the key to the start position. You should have continuity

This gives NO CONTINUITY when key is turned to START or RUN

***Wondering if you meant to specify two different terminals here? - would this not put full cranking voltage on the magneto? Did you mean NO continuity between B & M?


Result #2 - for ORIGINAL SWITCH

B to S gives continuity with key in START, OPEN when released to RUN

B to M gives OPEN in START & RUN (same as for the NEW switch)