instrument cluster weirdness

[wolfsbrg8v at bellsouth.net (wolfsbrg8v@bellsouth.net)]

Last night I replaced the instrument cluster, which has developed a broken trace on the flex circuit, with another used one, supposedly from the same year Scirocco (84) and which looks visually identical, MFA and all.  The replacement unit works fine -- except -- ONLY when the headlights are off. As soon as the lights are switched on (even the parking lights), the tach, fuel gauge, temp gauge and instrument lights all die.

I researched this in the .org archives and a couple similar problems are in there, and the advice was to check for a ground problem, and there was no response as to whether that solved the problem.  Anyhow I can't see how a ground problem could suddenly develop when all I did was exchange the clusters.  I was very careful to disconnect the battery first, take my time wrestling the cluster out, etc.

Anybody ever had something like this happen?  Are there differences in the pin-outs of the cluster connectors from year to year in that era, 1983-85, that could account for this weirdness?  Any help most appreciated!

Leo
84 Wolfsburg