i recently found the cluster grounds on an '85 300TD were bad. there is a trace on the PC board that starts at the round plug pin and follows over to a soldered tab on the board, from the tab the ground goes to the speedo pod in the middle. the trace was bad from the pin, and the solders on the metal tab were cracked. this bad ground situation caused all sorts of strange behaviour in the gauge cluster lighting. i ended up running a wire between the ground pin on the round plug and the soldered tab, and re-soldering the tab, and this fixed the issue. something to look out for.

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punkinfair