Fellow w123 Caretakers/Guru’s/PP board members,

I’ve happened upon a vexing short and, at the end of my abilities, wonder if I could tap the wisdom of the board to short it out.

I’ve a Hunter green 1985 300TD and was grafting a USB-2 port from a new sound system into the passenger side window switches when I created a short.

Instrument cluster and center console lights went out. Then I found that by jumping from the blue wire to the red or green wire the cluster lights would turn on.

However, all was not normal.

While with the jump the cluster lights would come on there were irregularities

1) They were on all the time, not just when the headlights were on.
2) The rheostat now dimmed not the cluster lights but the shifter light
3) The buzzer that indicated the headlights are on when the key is in no longer functioned

How odd. I thought and started to try to get to the bottom of things.

My first guess was the short was in the cluster circuit board, I swapped it out with one than another good board and no change in symptoms. Cluster circuit board ruled out.

My next thought was that the short was in the plug. Took that apart, no short.

Next try was the headlight swithch. Got a new one, swapped it in, symptoms exactly the same.

Any thoughts on what to try next?

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