73 FJ40 Won’t Start

[Nolacajun75]

The starter solenoid takes a good few amps to throw, especially when they're old and tired. It's also a big electromagnet (inductor) so current lags behind voltage, which can cause the ignition switch to arc.

While the bulkhead relay (not solenoid, since its only function is to actuate another set of electrical contacts) is not original, its not a bad upgrade in a system which is known to have a weak ignition switch.

While some of the wiring needs tidying up, it looks like some effort has been made.
I'd recommend printing out the toyota diagram as a starting point, and then editing it to bring into line with what you have.
You'll probably find that it's not actually that much different, and then decide what to do.

FWIW, my money is on a corroded ignition switch connector wire/terminal

Okay Roger that tomorrow I will draw out a schematic of what I have going on.

 

[Nolacajun75]

Only different note, can anything behind the gauge cluster cause this problem. Looking behind my gauge cluster I noticed this small transistor looking thing with three wires coming from it that was not connected and broken. This little transistor looking thing be purchased and replaced. I don't even know what it's for. Plus the back of my gauge cluster looks kind of rough. Not sure if it's causing any issues or not though. I don't think it would cause this type of starting problem though.

 

[73FJ40]

While the bulkhead relay (not solenoid, since its only function is to actuate another set of electrical contacts)

For the record, the relay in question is what was used on millions of Ford vehicles here in the US as a starter solenoid, which is why it's referred to as such.

 

[DeskJock]

That transistor is a work around. It could work as a low voltage/ amperage relay.

 

[45Dougal]

That "transistor looking thing" is a solid state voltage regulator which has been added because the mechanical voltage regulator in your fuel gauge has stopped working.
You could replace it with an LM7807 or similar, or alternatively you could try and clean your fuel gauge and get it working again. This is probably your best bet off your more mechanically minded.
This is why your temperature gauge has stopped working btw, because along with the fuel gauge it uses the regulated 7V as a supply voltage.

 

[45Dougal]

For the record, the relay in question is what was used on millions of Ford vehicles here in the US as a starter solenoid, which is why it's referred to as such.

Yea same here. In the old days, the solenoid was also used to push the starter gear into the ring gear, and the word stuck.

 

[Nolacajun75]

and the plug connections, which, Nate's instructions will help understand that issue.

I've kinda lost track of what worked and what didn't. did routing positive 12 volts to the solenoid cause the starter to engage and turn the engine?

Yes