so my ongoing charging quest with this car continues... been on the back burner the last couple months,,, to rehash, the alternator was removed and tested at 2 different stores and tested OK, i had the battery charged and tested yesterday since its been sitting, and the store said it tested OK. I finally poked around with a volt meter at the alternator harnessd and got the following results:

alternator harness with key off: large wires = battery voltage (11.99), small wire= no voltage
with key on- large wires= battery voltage (11.99), small wire= 1.75 v
with engine running after GP shut off= large wires= 12.65, small wire= 14.5-15v, at this point the reading across battery terminals is 11.57v

when poking around with meter probe on the back of the alternator harness, the readings seemed to be varied depending on where i made contact (at the wire vs deeper in touching closer to the alternator pin itself... sometime 11.75 ish to 12.75 ish.. this leads me to believe that the harness wires/contacts maybe be suspect.. they are pretty corroded, the wire connect contacts are corroded and the harness contacts that plug into the alternator seem pretty worn, and opened up where they may not be making a tight solid contact.

my questions: where do i get a new alternator harness? i've looked around online but cant find a place that sells it.
is there anything else that could cause a higher voltage at the alternator but lower reading at the battery?
do those voltage readings when the car is running seem right?

one other thing i think i should mention is there is an electric fan on the radiator that seems to run all the time if the key it on. not sure if that is normal or some thing the PO put on..

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1981 240D ... 265k
1977 240D ... 265k
1977 240D ... 250k