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evan_geno

918H Electrical Problems

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evan_geno

Hello everyone. I have been having problems with my Agco Allis 918H with the 18hp Kohler engine. Basically it is not starting at all with a full battery. Acts like a safety switch is not on. I checked all safety switches and they all seem to be in order. I took the steering wheel off and found a wire going to ampmeter was melted or worn down. I replaced this wire. I dug deeper and found some wires coming from the interlock module (whatever this thing is) had bare wires showing. I replaced the sections of wires on this and still don't get any starting. I tested the solenoid and that seems to working good and also tested starter and breaker switch and thats good too.I also tested the key switch and thats good. Lights work and the fuel shut off solenoid clicks on when key in run position. I have a 4 pole solenoid and if I take the blue and red wire and put them on the bottom pole, i can get it to turnover. So not sure if that interlock is damage or not. This thing has a lot of wires coming from it and goes to a harness spider webs to the rest of everything. Does anyone have wiring schematic for this? Your help would greatly be appreciated!

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GrincheyOne

I have found that most of the OEM starter solenoids do not have permanent activation coil connection to chassis ground. The interconnect module resolves the issue of what safety switches are in their appropriate "safe" state. closed and/or open, and provides a chassis ground to the second terminal on the solenoid, thus completing the coil circuit in the solenoid. After market solenoids like "Duralast" have the ground side of the actuation coil attached to the casing and only require the Positive voltage from the "S" terminal on the ignition switch to activate the coil and close the internal contacts providing positive voltage to the starter.

On tractors without a fuel shut off solenoid, the ignition switch "truth table" for the start connections could just read "B&S" thus killing power to accessories (like lights) while starting.

So concludes "solenoids 101" LOL

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BLT

There was a similar problem with some Sunstars with along with a few Sovereigns with Commands and it turned out to be a significant voltage drop in the signal wire to the starter solenoid. Could be your problem. You can try a jumper wire from the solenoid spade to the (+) of the battery to see if that makes a difference. If that is the case, a quick fix is to install a Bosch type relay in the circuit. The trigger coil of the relay only draws milliamps. You remove the existing signal wire from the starter solenoid spade and connect it to term 85 of the relay, then make a ground wire for terminal 86 and that completes the signal circuit. Then you need to make a wire from the starter power wire from battery, connect it to the post and then run terminal 30 of the relay and lastly run a wire from terminal 87a of the relay to ground. Try it out. That should take care of the 'cranky' start problems.:D On E-bay there are relays available for around $5.00 postage paid. The dry circuit terminals are good for about 30 amps.

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evan_geno

Is it possible to bypass the interlock completly. Seems like you could ground the G wire on key switch directly to bypass the interlock and maybe put power to L wire directy any thoughts?

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PhanDad

I think you're reading the wiring diagram incorrectly. The switch G wire is grounded directly (the wire is shown going from the switch to the interlock module terminal where it "continues" up, to the left a bit, then up again to the battery "-" terminal and the main ground wire (black wires).

If you look at the ignition switch function diagram at the lower left of the diagram, you'll see the switch L wire has power in both the "run" and "start" positions and not in the "off" position.

The interlock module works by taking away the "ground" connection from the various safety circuits rather than the old way of preventing the "+" voltage from getting to the device. If you follow the start wire from the switch, you'll see the "+" voltage go directly to the "hot" side of the solenoid (green wire); to complete the circuit on the "ground" side of the solenoid, the current passes through the trans safety switch and PTO safety switch and then goes to the interlock module. Then the interlock module decides if the other monitored conditions are met (operator in seat maybe?) the module lets the "start" circuit go to ground.

So if you wanted to by-pass the interlock module for start and have the Trans and PTO switches in effect, you would ground the circuit right after the PTO switch (tan wire) but you'd lose the other safety functions.

Hope the above makes some sense. And if I've got it wrong, I'm sure someone will correct me.

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GrincheyOne

Bill, The electrical logic purpose of the IC module is to provide the ground to the solenoid actuation coil via normally the yellow and green leads. Thew + side of the activation coil is provided by nominally a blue or purple wire from the S terminal of the ignition switch. the S terminal gets its + voltage from the B (breaker) terminal when in the start position. The G terminal is sometimes physically attached to the case of the switch, and if not has to be physically connected to ground (depends on the switch. I have both types here.

There are some variants of the aftermarket solenoids that provide the L + voltage from their second terminal, which interrupts when the coil is activated. (turns off accessories), but this is n the battery side of the breaker!

END - Solenoid 102! wah

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GrincheyOne

Bill,

The electrically logical purpose of the IC module is to provide the ground to the solenoid actuation coil via it's (IC) yellow and green leads. The + side of the activation coil is provided by nominally a blue or purple wire from the S terminal of the ignition switch. the S terminal gets its + voltage from the B (breaker) terminal when in the start position. The G terminal is sometimes physically attached to the case of the switch, *and if not has to be physically connected to ground (depends on the switch. I have both types here. *if you need to ground the magneto lead and stop the engine.

There are some variants of the aftermarket solenoids that provide the L + voltage from their second terminal, which interrupts when the coil is activated. (turns off accessories), but this is on the battery side of the breaker!

END - Solenoid 102! wah

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evan_geno

If I ground the yellow wire directly on the solenoid, I can turn it over with the key just fine. Problem is, it wont start the engine this way. I checked for spark on spark plugs and they show spark but maybe not too hot of a spark. Is it possible there is a wire being grounded somewhere? Seems like the engine should start if I can turn it over by grounding the yellow wire of the solenoid. Everything else works fine, headlights, and fuel solenoid. I think I'm lost! lol

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PhanDad

The interlock controls the "ground" connection of more than just the starter solenoid. One of the grounds it can make is the mag "kill" ground. On the wiring diagram, look at the "M" terminal of the ignition switch, you'll see that a white wire runs from there to the engine connector to kill the spark when you turn the key off. BUT there's a second white wire connected to the "M" terminal; it comes from the interlock module. If the safety switches aren't satisfied, the interlock grounds the mag, killing the engine or preventing it from starting even if the engine is turning over.

As Bob stated, the issue is either with the interlock module itself, or one of the safety switches. Too check the safety switches, jumper all three (seat, PTO, Transmission) and see if the tractor will start and run (make sure the PTO is off and transmission in neutral). If it does, un-jumper the switches one-at-time to see which one is the bad actor. If the tractor won't start and run, then it's probably something with the interlock module, including it's power supply source ("L" terminal of ignition switch).

And as a last thought, you checked the seat safety switch, but are you sure it's making when you're in the seat? I've had one bind and not make when seated, but when manually pressed it did. That's an easiest one to bypass.

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BLT

The following safety starting and running conditions must be met for all electrical wiring,switches and related components.1.All units must be tested for correct wiring and function of all circuits and switches.2.Engine operation must stop when the following conditions prevail:A. Ignition switch is placed in the off position.B. The operator is not seated with either the transmission or the PTO in theengaged position and parking brake not applied.3.Engine must not start by conventional means unless all of the following conditions aremet. Each condition must be checked thoroughly to insure proper operation sequences:A. Ignition switch is intentionally placed in the start position.B. Shift lever is in neutral.C. The PTO switch is in the disengaged position.D. The operator is seated. (On most models.)*E. Clutch/brake pedal must be fully depressed.4.Engine must remain running if operator is seated and the following conditions are met(Check thoroughly to insure proper operation):A. Transmission is engaged.B. PTO is engaged.5.If operator is not seated, the engine must continue to run only if the following conditionsare met:A. PTO is not engaged.B. Transmission is in neutral.*C. Parking brake pedal is set.6.Function of seat switch must be tested with switch mounted in proper position.*On those models shown as equipped with a foot pedal switch.NOTE: ALL SWITCH POSITIONS SHOWN WITH TRACTOR PARKED, ENGINE OFF, NOOPERATOR ON THE SEAT, AND PARKING BRAKE SET. (On most models.)

918StartCicuitCmmnd.jpg

918SafetyStartCicuitCmmnd.jpg

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PhanDad

Bob,

I see the wiring diagrams you posted are from the 1996 version of the Electrical Information Manual. I could only find that manual at the Briggs site back to 1998. And it doesn't have the correct Command diagrams like you used above.

Do you have a link to an electronic copy? Or an electronic copy you can send me? I think you already have my email addie, but I'll PM it to you anyway.

Thanks.

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evan_geno

Well thanks everyone for the schematics. I got her running. I bypassed the interlock by ground the pole on the solenoid where the yellow wire goes. I don't think I could get it running before because it was extremely flooded. Even mowed today with it! I just got to be careful with everything when starting without any safeties. All safety switches check fine. I think something inside the interlock is fried. I looked into a new one, there over $100. I'll stick with my free fix lol. Thanks again.

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