Ok, going through a 1980 Williams Black Knight and I am trying to get the GI lit. Here is what I have done:

Reflowed any connectors on power board
New GI connector, etc. with trifurcon pins
Check all fuses, etc.
Checked continuity across multiple parts of the GI sections.

When I measure the VAC at the bulb sockets for GI, I am getting the correct 6.5-7 VAC at the tabs on all. Connector going out of PS measures the same as well.

Am I possibly missing a ground or something? Could this be the GI relay? No GI works even the backbox as well.

Let me know if anyone has any ideas!!

Yes, new bulbs have been put into the backbox and some areas in the playfield. No change, but tabs appear to have correct readings for VAC. I will get some pics of the wiring connections to include here.

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Still no GI after disconnecting that connector.

Going to drop a pic of all my boards in case something is out of place. Game plays fine, just the GI out though

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I’ll check the connector again, but didn’t come across any shorts. The thing that is throwing me is all the GI in the cab and backbox has the 6.3-7VAC when I check it. Backbox basically comes out of the power board right into the light panel pretty much.

I’m going to try and disconnect the GI to the playfield and see if the backbox gi comes up. I disconnected the backbox gi and no change

No change if I separate the backbox or cab gi.

Yes, when I measure the vac at the sockets I get the 6.3-7ish. Quick question on that, both tags should measure the same?

That was it, I desoldered, cut back and stripped some new wiring for both that lug and the lug on the other side of the transformer. GI works fine now. Had looked at that beforehand, but they didn’t seem bad or needing to be resoldered.

Thanks again @PINTEC, I knew it was something small I was looking over.
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This is correct. Measured both tabs in respect to ground.

I believe I did measure across the bulb at one point and did get the “0” reading.

I even checked continuity through the connector in the backbox to the transformer at one point and it beeped on each side.

Game had incandescent bulbs in backbox during my testing and I swapped them out right before I cleaned up the transformer wiring. If you look closely, the playfield GI still has them(for now).