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Since your truck has two solenoids, you have the auxiliary intake heater -- kind of a useless appendage, unless you live way up north. You can see the heavy wires running from the large glow plug in the intake to the solenoid -- ignore this solenoid, and focus on the other one. The second solenoid is for the glow plugs in the cylinders.

Use a test light and see that there is 12 volts on one side of the large terminals - key off - this is the battery feed. Now, disconnect one of the small terminals, and key on - time is short so hurry . Use your test light on the small terminal and the post where it came from -- which one has 12 volts? This will determine which wire is hot and which is ground.

The "hot" is supplied form the switched battery circuit, the "ground" is supplied by the PCM. The ground is timed depending on temperature - ambient and -- (hmm, coolant or oil, need to check)

When all of the wire purpose is figured out, then you can test at key on (for a few seconds) the small PCM ground and the large solenoid output post. The small ground and solenoid output should operate at the same time. To test the small ground, you will need to put the test light clip on a positive battery post.

The control wires you asked about are separate from the PCM
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