instrument cluster ground

RedFish said

The factory engineers added the single ground at the headlight switch which is the same result as speedo. The problem is over time the screws loose their connection to the copper pad and to the pot metal threads so the total resistance accumulates and varries from one point to another. A tinned ring terminal against the copper pad is taking a more secure , direct, dependable path. Soldering the wire to the copper trace would be optimal only if vibration and the yank factor were eliminated.
Not so much electrical theory or proof from a ohm meter, just attempting to improve upon the next 45 years service while renewing.
A lot of ground wires that aren't routed in a proper manner might repeatedly break the plastic bulb sockets when yanked too so... Who knows whats the best plan.

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It almost seems like we're barking up different sides of the same tree (and I'm pretty sure that's the most mixed metaphor that I've ever posted).

Since the pot metal chassis of the cluster is the common ground point for all the lights and anything else that draws power from the cluster positive (hot) it seems to me that soldering to the metal of the chassis would be the ideal, but soldering to pot metal is mighty difficult.

The point of the ohm meter reading was to show that the resistance of the cluster chassis is low enough that it makes no practical difference exactly where the ground wire we're adding is connected. Wherever we put it, the connection should be as low resistance as possible.

What I have been doing is just a ring terminal under the head of any screw that threads into the cluster chassis. I might sand the chassis and add an internal tooth lock washer and some grease to improve the connection, but any improvement would be very small. The treatment of the other end of the new ground wire should be similar and its routing and length need to be thought out to avoid problems down the road.

ATB

BC