The fuel out starter inhibitor system is an optional extra, so yours may not have it at all.

Thanks for the good info.
The black wire problem ive seen before. The starter inhibter relay I overlook if its in the manual i was looking in. Will let you know the outcome mon.

Another thing I thought of (but you may already have checked) is the control signal wire that connects to the starter solenoid.
This wire is notorious for breaking on the 4Y engines (among a list of other wires that break).
So, if you are hunting a starter problem on a 4Y in a 7F, make absolutely sure the black control wire at the solenoid connector is not broken. Physically pull on the wire, even if it looks OK.
I have seen them break but still be held in place by the wire insulation a couple of times.

You are referring to the "starter relay" located in the relay & fuse box in front of the battery??
The wiring in my manual shows that WHITE/blue tracer is power input to relay.
Large BLACK wire is power out of relay (leading to starter solenoid).
Small BLACK wire is the relay control signal wire (coming from starter NEUTRAL circuit of the combo switch on steering column).
BLACK/yellow tracer is the grounding wire for the starter relay operating coil.
There is not any diode in the starter relay circuit (though the relay might have an internal snubber diode).
The difference in the Ohms you refer to is likely just because you are measuring the resistance of the operating coil in the relay when plugged and measuring infinity when unplugged.
You are aware of a separate fuse in the box that serves the starter relay circuit??

If this is an LP powered truck, another possibility (maybe slim chance) is that the truck features a cranking inhibitor relay to prevent operation of the starter when the fuel cylinder is empty. First thing to determine is whether the truck has a basic "Low fuel" pressure switch (mounted in the LP regulator liquid line plumbing). If the truck does not have a low fuel switch it will not have the fuel out starter inhibitor.
You can determine if the truck was built with the fuel out inhibitor relay feature by looking on the inside of the cab front panel for the actual inhibitor relay. You will have to remove the toe board sheet metal panel to see this. The relay would be mounted to the panel just to the right of the power steering hoses and to the left of the inching cable.......just above where the inching cable attaches to its anchor. The relay is one of the round canister type and will have 4 wires serving it.....ORANGE, BLUE, WHITE, and BLACK. The BLUE and ORANGE wires have bullet style connectors in them (for bypassing the relay if relay fails). If you find this relay where I described, unplug the BLUE and ORANGE wires from each other and then plug the ORANGE and BLUE wires (that lead off toward the dash above) together. If the starter engages after connecting those 2 wires together, it means that the "fuel out starter inhibitor relay" was interrupting the circuit to the starter relay fuse.................but this does not prove the inhibitor relay is defective.
If this system is in the truck, the fuel out lamp on the dash and the WHITE wire of the inhibitor relay are both provided with a path to ground (when the low fuel switch closes).
Even if the low fuel lamp is burned out........the inhibitor relay still functions. Which means you will not see the lamp telling you that the tank is empty, but the starter will be inhibited by the system.