M1088A1 Starting Issue

[Ronmar]

I believe matthew is correct, 15PSi low oil switch(S27) is on a little manifold on the drivers side of the block a little above the oil pan just forward of the starter...

That provides the ground path to energize K11 and the dash low oil idiot light. When it hits 15PSi it opens the circuit to ground, puts out the dash light and de-energizes K11 which shifts control power from the start switches to the alternator.

 

[BeetTrucker]

Is this what you are referring to?

 

[BeetTrucker]

This is the one that I got.

 

[MatthewWBailey]

Is this what you are referring to?View attachment 933992

I have a 2004 A1 with '99 dated 3126 and I have the same One-Wire oil sender. The big angled one is the sender for the psi gauge. The one below it is the switch which activates the idiot light and K11. Trouble is, Cat is sourcing the 3 wire sender which seems to be off later models and C7's. I'm not sure how to wire in a 3wire sender to the one wire trucks. That's a @Ronmar or @GeneralDisorder question or other masters on here.

BUT, it's the pressure switch that needs replacing if you're not getting K11. Unless, as I my case, it's not fully connected. Check the wire connector and make sure it's fully plugged in and not corroded. Those plugs are tricky.
In this photo, the device in the lower right is the psi switch. It's connector is not in frame but it's a pesky little bugger to get snapped together properly.

 

[Ronmar]

That silver one is the gauge sender. The switch Is in the background of your pic(black plastic body against the block, harness toward the rear). Also seen lower right of Matthews pic, against the block, painted yellow.

that parts picture you added of the 3 wire oil pressure sensor, looks like it may be an oil pressure sensor for the HEUI system(found up on the HEUI pump?

the part that will cause no idiot light/no crank is a simple 15PSI oil switch. Its not a cat part, the ones used on the LMTV were made by Nason. If you unplug yours and jump across the two pins in the truck side cable you should get a low oil idiot light in the dash when you turn on the ignition…

can be replaced with a common 15PSI low oil pressure sw. The Nason has 2 leads, one connects to ground and the other runs up into the dash wiring. A standard single terminal sw will work, you just need to get the correct wire of the two (one that feeds up to the cab) attached to the single sw terminal and it will ground thru the switch body to the block like most auto applications do… the wire you want is the one that lights the oil light when grounded(ign sw on)…