I was repairing the erratic fuel gauge and think I have it fixed but may have damaged something else.

My 4 instrument panel bulbs do not work, the ones controlled by the rheostat. The dimmer rheostat wire is grn/brn and goes to instrument panel C5 which has a foil lead to a little rectangular box with the upper right corner at an angle. The box is shown in the 700/900 faqs under electrical instruments/Fuel Gauge Fluctuates or Fails to Work/ and the writeup is Cluster Cleaning/Disassembly and Connector Wires. There is a picture there and the box i'm referring to is in the the upper right corner. What is it? I think it is something to do with the instrument panel lighting. I wanted to see a foil under this box, took it off and now my 4 instrument panel lights do not work. I did solder the bottom 4 pads of the little box to ensure a better electrical contact (may have damaged it). What is the little box? It looks like there is a little PC board inside.
Another picture of the little box is at the top down a little farther in the faqs by 3. Poor Instrument Panel Contacts. [Response: Tom Irwin]
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Mine:3-940s running, 1-740, 2-940 parts, dtrs:3-940s running