M1079 start button won't trigger the starter.

[MapleNomad]

Alright fellas i've been following a few different threads here to try figure this stating issue but i was a 91S not a 91B so i don't have the same wealth of knowledge as the light wheel guys. I got a M1079 1998 witec 3. When you flick on the power switch on the dash, there are no clicks or start up sounds (except one relay i cant remember right now) and the start button does not activate the starter solenoid. Bypassing the starter solenoid (wall mount solenoid not the starter itself) turns this guy over. Ive tried the trick where you take the k1 starter relay out and take a jumper cable to 30 and 87, to no response. The starter solenoid has been replaced with one from Midwest military industries/didn't fix. I have new 24v relays for K1 and K19/ nothing. And brand new 1000cca batteries/ again nothing. Any hints towards what to do next would be appreciated.

 

[NDT]

Do you have both 12 and 24 volts present at the power points at the PDP? Did this truck just develop this issue or did you get it this way from surplus?

 

[GeneralDisorder]

Is the transmission display lit up and does it show N?

If the trans computer doesn't power up and go to N it will not enable to starter via the relays it controls.

 

[MapleNomad]

Is the transmission display lit up and does it show N?

If the trans computer doesn't power up and go to N it will not enable to starter via the relays it controls.

Yup, neutral light kicks on when you flick on the power switch.

 

[MapleNomad]

Do you have both 12 and 24 volts present at the power points at the PDP? Did this truck just develop this issue or did you get it this way from surplus?

Where do i confirm that in there?

 

[MapleNomad]

Where do i confirm that in there?

Also this truck was sitting in the woods of Georgia for over 7 years after it was bought from an auction. Before i grabbed it.

 

[Suprman]

So you have never seen it run? If no trans display someone probably cooked the trans tcm trying to jump the truck with dead batts. I have a replacement here. If its 7 year old fuel and fluids I would drain and replace it all. Flush back the fuel lines and probably replace the lines. Definitely new filters all around before I even tried to start it.

 

[MapleNomad]

So you have never seen it run? If no trans display someone probably cooked the trans tcm trying to jump the truck with dead batts. I have a replacement here. If its 7 year old fuel and fluids I would drain and replace it all. Flush back the fuel lines and probably replace the lines. Definitely new filters all around before I even tried to start it.

Oh the thing runs and drives, As i said in order to turn on the truck on i hit the power switch then bypass the starter solenoid. Although i really should drain out that old fuel and finally do the service. That wouldn't hurt.

 

[Ronmar]

Ok, for a 98 with WTEC 3, when you turn on the ign sw, K11, K24 and K26 in the panel must energize. K11 and 24 are controlled by the oil pressure sw, so you must also get an oil idiot light. K26 is the neutral start relay controlled by the trans controller.

K24 and K26 provide the path for the start sw to energice K01 when pressed.

K11 keeps the alternator offline until the engine is running and sees 15PSI of oil pressure then it de-energizes and powers the alt regulator with pins 30-87A. K24 also de-energizes above 15 psi disabling the start button on a running engine.

K01 energizing in turn energizes the aux start relay down on the frame when you push the start button . There is a thermal safety circuit that some starters have(plug on front of motor) that completes the aux start relay circuit to ground. On units without this thermal sw, the plug has a jumper and it is taped back into the harness.

So what goes click when y0u turn on the ign, and what goes click when you push the button?

here is a one page condensed diagram of the start electrics.

 

[MapleNomad]

Ok, for a 98 with WTEC 3, when you turn on the ign sw, K11, K24 and K26 in the panel must energize. K11 and 24 are controlled by the oil pressure sw, so you must also get an oil idiot light. K26 is the neutral start relay controlled by the trans controller.

K24 and K26 provide the path for the start sw to energice K01 when pressed.

K11 keeps the alternator offline until the engine is running and sees 15PSI of oil pressure then it de-energizes and powers the alt regulator with pins 30-87A. K24 also de-energizes above 15 psi disabling the start button on a running engine.

K01 energizing in turn energizes the aux start relay down on the frame when you push the start button . There is a thermal safety circuit that some starters have(plug on front of motor) that completes the aux start relay circuit to ground. On units without this thermal sw, the plug has a jumper and it is taped back into the harness.

So what goes click when y0u turn on the ign, and what goes click when you push the button?

here is a one page condensed diagram of the start electrics.

So while im sitting here testing these spots, would yah happen to know what the stop sign idiot light means.

 

[MapleNomad]

Ok, for a 98 with WTEC 3, when you turn on the ign sw, K11, K24 and K26 in the panel must energize. K11 and 24 are controlled by the oil pressure sw, so you must also get an oil idiot light. K26 is the neutral start relay controlled by the trans controller.

K24 and K26 provide the path for the start sw to energice K01 when pressed.

K11 keeps the alternator offline until the engine is running and sees 15PSI of oil pressure then it de-energizes and powers the alt regulator with pins 30-87A. K24 also de-energizes above 15 psi disabling the start button on a running engine.

K01 energizing in turn energizes the aux start relay down on the frame when you push the start button . There is a thermal safety circuit that some starters have(plug on front of motor) that completes the aux start relay circuit to ground. On units without this thermal sw, the plug has a jumper and it is taped back into the harness.

So what goes click when y0u turn on the ign, and what goes click when you push the button?

here is a one page condensed diagram of the start electrics.

Okay so far flicking on the power engages k26. And hitting the start button engages K1.

Okay. Not sure if this is healthy for it but removing 11 24 &26 then placeing them in there slots individually allows me to hear an audible and physical click.

 

[GeneralDisorder]

Okay so far flicking on the power engages k26. And hitting the start button engages K1.

Okay. Not sure if this is healthy for it but removing 11 24 &26 then placeing them in there slots individually allows me to hear an audible and physical click.

Won't hurt the relays but doesn't prove the contacts inside them are any good. Just indicates they are being triggered to close (open for the NC contacts). Make sure you have 5 pin relays where you need them, and 4 pin relays only in locations that don't have the NC contact (87A) populated in your panel. And of course must ensure you have 12v and 24v relays where required.

 

[MapleNomad]

So k1 30 to 87 gets 1.8v when you hit the start button. K1 30 to ground gets 24v. So could it be something to do with the cable assembly around the starter relay against the wall.

 

[Ronmar]

Yep, plugging them in and out is fine and a valid coil function test.

if k1 is energizing, beyond testing its contacts, all the rest of the in cab start circuitry is probably OK. You could rule out its contacts with a test jumper pin 30-87, which should crank the starter…

K1 sends 24v down to the large aux start relay on the drivers frame rail. The ground side of aux’s coil goes thru a thermal sw to ground(upper right on the drawing i provided).
With a voltmeter you should be able to see 24v on a small aux terminal when K1 energizes….

 

[Ronmar]

Only seeing 1.8 v 30-87 but seeing 24v30-gnd at K1 does indicate a poor path to gnd thru the aux start relay on the frame…

 

[MapleNomad]

Yep, plugging them in and out is fine and a valid coil function test.

if k1 is energizing, beyond testing its contacts, all the rest of the in cab start circuitry is probably OK. You could rule out its contacts with a test jumper pin 30-87, which should crank the starter…

K1 sends 24v down to the large aux start relay on the drivers frame rail. The ground side of aux’s coil goes thru a thermal sw to ground(upper right on the drawing i provided).
With a voltmeter you should be able to see 24v on a small aux terminal when K1 energizes….

Yeah jumping the k1 30 to 87 doesn't kick on the engine. I have had to tap both terminals on the large aux start relay to turn the engine on.

 

[Ronmar]

Disconnect the 2 small terminals at the aux start solenoid. One wire should have a short circuit/low resistance path to ground. The other wire should have 24V from K1 pin 87 when K1 energizes…

 

[MapleNomad]

Disconnect the 2 small terminals at the aux start solenoid. One wire should have a short circuit/low resistance path to ground. The other wire should have 24V from K1 pin 87 when K1 energizes…

So after disconnecting to small terminals it seems like the ground cable isn't grounded. I put my multi meter on the small start connector (pos) and up against the frame then hit the start button and got 24v. Shoulds i trace the ground cable... Or should i make small ground cable straight to the frame. Going through all the bundles of cables looks like a hassle.

 

[MatthewWBailey]

So after disconnecting to small terminals it seems like the ground cable isn't grounded. I put my multi meter on the small start connector (pos) and up against the frame then hit the start button and got 24v. Shoulds i trace the ground cable... Or should i make small ground cable straight to the frame. Going through all the bundles of cables looks like a hassle.

All 3 major ground points are painted with CARC so they don't function. I think they thought that star washer would be enough to cut thru the paint. Every truck seems to suffer from this. RE drill frame on both sides to make a clean attachment for the Alt gnd, Starter/batt gnd, and cab ground. The starter ground is kinda hidden but behind the bolt circled in red...
All kinds of things start working after this very big job.

 

[Ronmar]

In the case of the ground for the aux relay look in the wire bundle adjacent to the starter. They put in a plug on that ground lead to connect to a thermal sw in the forward end of the starter motor. Stops cranking when motor overheats…

If you have one it will be plugged into a receptical on the front end of the starter motor. If you dont that plug has a jumper in it and is taped back into the wiring bundle near the starter.

or you can make a new aux relay ground lead. and run it to a convenient ground point.

as Matt said, check your grounds, mine were a mess also!