Rad Fan intermittant - killing the battery

[SJ]

Patient: 1988 5000Q

Symptoms:
Battery goes dead after car sits around a couple of days.
Been doing this all winter.
Very intermittant.
Couple days ago found out it was the radiator fan that was going on by
itself. Even though the car was not driven for two days.

Troubleshooting so far:
Disconnected the fan after-run thermoswitch, and the problem remains.
Disconnected ground from the fan motor. Attached lamp with long wire to Hot
terminal of motor. Lamp is inside the car now so I can see it go on when the
problem occurs. No results on this yet.
Schematic shows 3 relays that control power to the fan -
relay 2(2nd stage)
relay 12(3rd stage)
relay 15(after-run control unit)

The most likely culprit is the 15 relay listed as "Rad cool fan After-run
control Unit". I cannot figure out how it works. The schematic does not show
the relay guts, only the pinouts.

I know pin 30 is power in , and pin 87 is power out.
I think pin 5/T (thermoswitch) is one end of the coil and 6/31(ground) is
the other end of the coil.
But I'm at a loss regarding the functions of pin 3/15 and pin 4. Pin 4 goes
to the A/C programmer, so I figure this pin is internally connected to the
coil. A/C is switched on, fan goes on.

Pin 3/15 is connected to the A/C Hi-Press sw, and the center hot lead of the
Rad cool fan thermoswitches, and the hot end of relay 2(Rad cool fan relay
2nd state).
For this circuit to work, 12 volts must always be present at pin 3/15?  Even
with ignition off?

Looking for some BTDT on this problem.



SJ
85 Dodge PU, D-250, 318, auto
85 Audi 4k - - sold but still on the road
88 Audi 5kq
90 Audi 100q