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Discussion Starter #1
I recently acquired an MTD YardMan 8.5 / 26. Machine does not have the model number tag anymore, but I believe it is a 2002 model year.
It was originally equipped with a head light, heated grips, and power chute control. The chute control motor and wiring is gone.

My problem is that with the engine running, the head light works, but with the grip switch in the on position, the grips do not get warm.
I hooked up a 12V lawn and garden battery to each grip individually, and they got warm rather quickly. So I know that the grips themselves are not burned out.

My knowledge of wiring is weak so any help would be appreciated.
 

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My guess would be to test the switch first, if you have a meter it will help greatly in testing.
 

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Discussion Starter #3
There are two short wires connected to the right hand grip with a plug on the end. Two wires come off the wiring harness and plug into that plug.
To test the switch, should I disconnect this plug, stick my meter probes into the harness plug and check for voltage with the switch on and then with it off? If I see voltage with the switch on can I assume the switch is good?
 

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There are two short wires connected to the right hand grip with a plug on the end. Two wires come off the wiring harness and plug into that plug.
To test the switch, should I disconnect this plug, stick my meter probes into the harness plug and check for voltage with the switch on and then with it off? If I see voltage with the switch on can I assume the switch is good?
Probably best to check the switch itself, using the Ohm function on the meter.
First, put the meter in the OHMs position and touch the leads together to verify that the meter needle moves to 0. If its a digital meter, the display should read 000.

Put the test leads across the switch (engine off of course) and with the switch in the ON position, you should see the meter reading 0 ohms, ie the needle will swing all the way to the right if it's an analog meter. With the switch in the OFF position, the meter should read infinite ohms, in other words, the needle will not move on an analog meter, or it will read in the megohms range indicating the switch is open.

If you get a high reading in the ON position, the switch is defective.

After you verify the switch, then you can try reading voltage on the pins. try putting the meter on the AC and DC ranges and see if there's anything there.

If you get nothing, start checking for broken or shorted wires or corroded connectors.

You might also check the output voltage from the connector where the chute motor used to be connected. If that is dead too, you might have a problem with the stator windings. If that voltage is good, maybe you can switch your grips to that connector and get power that way.
 

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:welcome: to SBF ahw2698

Can you turn the headlight off and then see if the grips get warm ?? Some machines only have enough power to run one or the other. Any chance it's a replacement engine or does it look original ?? Can you post the engine numbers ??

You should be able to take your voltmeter and touch the metal tab coming up from the body of the switch. You don't need to remove the connectors just pull them barely away from the switch body so you can just get the voltmeter probe in there. One tab you should have around 12-16 volts all the time and the other two should be switched. I think your switch is lighted that is why it would have three tabs. Power should be coming from the engine up the right handle bar to the switch to the right hand grip and then over to the left hand grip and then back down the handlebar and have an eyelet screwed to the engine or trans body to ground the circuit.

The below diagram isn't a Yardman but they are all similar.
.
 

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After 8 years of usage (or thereaboute), my heated grips stopped working too, and it turned out that the Connector between the engine's alternator and the Fuse for the grips had corroded. On mine, the Connector was located at the bottom of a drip loop, right where salty water and crud would collect and speed up the deterioration of the aluminum connection. Check it out before doing any other heavy lifting. I replaced mine with a solid wire.
 

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Discussion Starter #7
Something must be robbing power from the red wire before it gets to the switch. Probing the switch only shows about 5 volts. when I meter the output from the stator at full throttle, I get 14 to 15 volts AC from the yellow wire and 14-15 volts DC from the red wire. Are these readings what I should expect from the alternator?
 

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Something must be robbing power from the red wire before it gets to the switch. Probing the switch only shows about 5 volts. when I meter the output from the stator at full throttle, I get 14 to 15 volts AC from the yellow wire and 14-15 volts DC from the red wire. Are these readings what I should expect from the alternator?
Readings are in the correct ballpark.

Try removing the wire from the connector on the switch and see if that 5 volts improves.

Take a reading with the headlight disconnected as well and see if that makes a difference.

The AC and DC power come from the same stator, and there is a rectifie in the DC line to get the DC component, but a
short on either the AC or DC side will drag down the voltage on the whole stator

Check the grounding terminal(s) at the engine block, check all connectors/connections for corrosion.

Check that the wiring harness is not pinched and that the insulation on all of it is in good shape and not rubbed through. If you don't find the voltage drop problem there, then you might have to start ringing out segments of wire from the stator connections thru each segment (between each connector) to see is you have some broken strands inside undamaged insulation. This is where it gets to be a PITA
 
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