#4 Fuse blowing in an unusual way?

Here is an update: I removed the multi-function switch, and tested resistence on the DB/O wire to ground and got 4 millions or so Ohms. I'm new to electrical work, but from my limited knowledge this tells me I have a short to ground somewhere between the connector and the fuse box?

UPDATE #2: I saw that there is another circuit on a T/W wire from fuse #4 (see attached diagram) to the headlight switch. So I disconnected that harness and tested the T/W wire in the harness. It was reading OL on the meter to ground. Went back and tested the DB/O wire on the multi-function switch and now it was reading OL. Looks like it was the headlight switch. To further investigate I tested the pins on the headlight switch according to the test table attached. When I tested across D1 and D2 (with the wheel turned all the way left, in detent) I get resistance that fluctuates between open and closed. Will be ordering a new headlight switch. Thanks.

Okay. I replaced the headlight switch and the multi-function switch (because it had some issues with the intermediate wipers anyways); however, fuse #4 is still blowing when turning on the lights. It doesn't seem to matter if I open the door or not (maybe it was just a coincidence before). What should I do now to find/narrow down the problem?

Hi, I have a bit of an update and need some advice. Here is where we are:
1. I'm not measuring resistance from the T/W to ground on the headlight switch anymore (with the fuse pulled out of course).
2. Now, I was getting resistance from the BR wire at the headlight switch to ground.
3. After pulling a large, diagonally situated, black plug against the firewall behind the battery on the driver's side (just below another white colored vertically situated plug), I am not longer seeing resistance on BR to ground at the headlight switch.

So, this tells me that the short somewhere from that big plug onward. Does anyone have a detailed wiring diagram, that shows the connectors and locations involved w/ the BR wire.

Update: I think I have misunderstood the fundamentals of testing for shorts in a circuit. As such, I think I need to learn some more and re-assess. I think this thread has been a bust and can be deleted. I will open an new thread, once I have a better understanding and can formulate my question better. Thanks.