Comanche Dies With Electrical Load

Vehicle is an '86 Comanche 2.5L.
Tested the battery at standing and charging, came to 12.8 standing and 14.7 charging. The alternator relay clicks, though that doesn't necessarily mean it's in good working order.
Any electrical load applied; headlights, taillights, hazards, blinkers, etc. kill the engine.
The clutch master cylinder is leaking onto the fuse box, though I moved it as best I could as I don't have the funds for a new master cylinder right now and I'm not sure which fuses, capacitors, and relays do what on the fuse box as the writing is barely noticeable.
Any thoughts?

Just got done starting her up again. Fired right up the first time. Turned on the heater, wipers, blinkers, head lights, parking lights, stepped on the brake, put it in reverse. Did just fine. Turned on the hazards and she started to die. Turned them off, ran correctly. Turned them back on, ran just fine.
What kind of weird electrical gremlin is this?

Sounds like there is either an intermittent ground, or short. It could be caused by fluid; when you said brake fluid was dripping on the fuse box that raised a red flag to me. See if you can't suction or mop up the fluid in and near the fuse box.

Sounds like there is either an intermittent ground, or short. It could be caused by fluid; when you said brake fluid was dripping on the fuse box that raised a red flag to me. See if you can't suction or mop up the fluid in and near the fuse box.

Turned out the positive battery cable was split, mass amounts of corrosion, and there were only a few strands connecting it to itself. Cleaned it all up, soldered it together, and she works like a dream.

Nice fix. I've had corrosion in the positive cable before, it causes all sorts of weird stuff to happen.