Sounds like the buzzer may be grounding through the tach. Is it an in dash tach or separate tach mounted on the column or someplace else? Where is the buzzer supposed to ground?
Yea that is what I was trying to determine... where the grounding was occurring, because there is a direct ground which is causing the contact (point of highest resistance) to heat up.
Maybe the resistance is too high for the buzzer to get enough current or the buzzer requires more current -
Who swapped the original speedminder stuff onto your replacement speedo?
OR do you have a repro speedo and speed minder mechanism as ONE unit?
And everything else is original?
IF you have repro speedo speedminder needle contacts etc...
DID you fully service your original parts? FULLY clean ANY contacting points for harness connections?
Did you ensure the plugs are actually contacting with zero ohms resistance?
The tangs on the bottom of the highram?
The packard terminals, did you remove the metal terminal ends from the harness plugs and use a fine wire brush and clean them and lube them with connection compound?
The resistance (current load) BEFORE getting to the highram may be too much for the circuit... There is NO DOUBT in my mind that a reproduction contact is going to be inferior by orders of magnitude to the original delco component.
For cleaning original harnesses...
I pin a harness down to a 6 foot long 2 foot wide piece of plywood with a sheet of paper which I draw out all the connections - label all the harness ends and wire colors, then unwrap the harness, clean the connections, and repair any damage, prior to rewrapping in harness wrap and installing the plastic ends which I run through the dishwasher a few times (in the utensil baskets).
I made a tool to remove the terminals from the plastic plugs using a piece of stainless tig wire which I hammered flat and then filed to the correct width. I made a loop on mine to wrap around my thumb so I can use both hands to manipulate the plugs under a dash etc when fixing wiring problems on "restored" cars... Sorting out wiring and glass fitment issues on "professional restorations" could be a FULL time job if I wanted it...