Those are "controlled lamps", just like on the playfield. I would test for DC voltage at those vs. the other controlled lamps in the game that are working properly. If you find a difference, you probably have an issue with that controlled lamp string. Could also be a bad socket. Try removing ALL the controlled lamps with a problem and see if you get voltage at either socket pin. Test with red lead in socket, and black lead on ground braid in head. If it checks ok, test one bulb at a time until you find the bad socket. Should see about 6VDC at one of the leads in each socket.

Ultimately, it's going to come down to a bad socket/bulb or a shoddy wire connected to the lamp section of the MPU/driver board in the head.

This is a Williams system 11.

In that case it would be Q66. Wouldn't hurt to check the other things I mentioned as well.
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There is no such thing in this machine. Controlled lamps are strobed, using the same power source for all strands. You are confusing this with the GI strings that DO typically have multiple fuses for each string.

The suggestions seem to be pointing the OP in the opposite direction regarding what the transistor actually does in the lamp circuit. Just replace Q66. It's the most likely cause and it's $1. Also, a transistor can test good and still be bad under load.

For future reference, the Q65 transistor grounds the circuit. It does not "provide voltage" in any way. The bulb sockets should ALWAYS have (+) DC voltage (through Q66). This transistor grounds the circuit to light the lamps, just like with a coil/solenoid in a pinball machine.

You see, there are two items at work. First, the voltage supplied to the lamp sockets (which is probably ok unless you have a bad socket/bulb or broken wire) , and 2nd is the ability for the game to ground those circuit and in turn, light each lamp.

Everything here is correctly stated. If the strobing circuit (voltage circuit) is working properly, the socket will have it's + voltage.

I see what you mean now. If the strobing circuitry is not working properly, there could be a problem with a transistor or other component in that circuit as well. I left out Q65 (the grounding trans.) in my response above (now revised).

It's time consuming enough to pull the board so I would replace them both at the same time. If that does not work, check output of U53 (pin 11).

I realize this. Nothing new to me here but thanks for trying.