Comanche Dies With Electrical Load?

You have a dirty or corroded contact between the battery and the wire that powers (headlights, tail lights, hazards, blinkers, etc).

The wire to the starter is not bad (it is a very large wire that connects directly to the battery clamp. The car would not start if that was bad.

The smaller wires that come off the positive battery clamp run everything but the starter (so your problem might be where the wires separate from the large wire to your starter).

I don't think that brake fluid leaking into your fuse box could cause this problem. I am guessing that brake fluid is not conductive, and that it cleans off dirt and corrosion. If so, it should not cause a bad contact--if anything, it should help a bad contact.

The problem is not caused by any one (single) wire in the fuse box. If just one wire were responsible, it would either be a short, which would ruin a fuse or melt a wire, or it would be an open circuit which would disconnect just one thing (such as just the tail lights).

MOST LIKELY CAUSE OF THE PROBLEM:

Most likely the problem is at the positive battery clamp (where the wires split off to the starter and the rest of the car). That clamp sometimes gets corroded by battery acid. You may have to remove the positive battery clamp by cutting off the wires, peeling back the insulation, and attaching a new positive battery clamp (they cost about $2 and are available at car part stores).

Some cars split wires off to the starter and the rest of the car at the positive battery clamp, while other cars split the wires a short distance from the battery.

TAKING OFF A BATTERY CLAMP FROM A BATTERY:

Your engine should not be running when you take off the battery clamps.

You should always take off the negative battery clamp first, because if your wrench accidentally taps a grounded piece of metal, it won't short. (A short could damage sensitive electronics in your car). The negative clamp is smaller than the positive clamp and it is connected to a black wire.

Once the negative battery clamp is off, you can safely take off the positive wire (it won't short if your wrench touches ground because the negative clamp was taken off).

When reinstalling the battery clamps, put the positive clamp on first. (That's the large clamp with the red wire).

Sorry to harp on making sure your battery is good, but batteries can give good voltage readings and be bad when tested under a heavy load like cranking the engine. I personally would replace any battery over 4 years old, but you can connect your digital voltmeter across the battery and have a friend crank the engine with the ignition disabled. The battery voltage must measure greater than 9.6 Volts after 10 seconds of cranking. If not, your battery can't supply the minimum voltage to run the fuel pump and vehicle's computer electronics etc properly.

Another reminder is that you can't measure the battery voltage after turning the engine off without waiting at least an hour to allow the "surface charge" to bleed off and get an accurate reading. Or turn the lights on for a minute and that should bleed the surface charge off so you can measure the engine off battery voltage which should be 12.5 Volts or more for a charged battery.

Make sure to disconnect the battery cables from the battery to clean their metal contacts with a wire brush before reconnecting them.