Help! 78 New Yorker Fuse box issues

Like Robert said pull the fuse box and check the wiring on the back side also.

Where exactly did it spark?
Which fuses are blown?
It sounds like you have a wire shorting out somewhere. Brake lights and headlights should be in separate circuits. If both of those fuses are blowing then you need to chase the wiring after the box.
Check the box to find out which side of the fuse has power coming in and which side goes out to the lights. Once you do that, check for a direct short to ground between the fuse connection going out and a chassis ground. If you have a short look for bare or damaged wires. You can move the harness around to see if the short goes away as the wires move.

A bad turn signal switch could cause the problem too. The brake lights and front side markers are joined at the turn signal switch. If it shorts out it can blow both fuses. The headlights are on the same fuse as the side markers.
I don't think the lights will work if the switch is unplugged. You can unplug the flasher and see if the brake lights still work after replacing the fuse.

I had similar circumstances with the 69 Coronet. Two steps have been taken since then:

1. Put a battery disconnect switch on in case of the worst
2. I stay out of the area behind the fuse box because I do not have the skill/info to go there. I get competent help from another Moparter on-scene.

Be careful.

I could only look at a wiring diagram for a 76. hoping it is simlar.

both of those circuits show a fusable link.
also you have some weird relay for power under the hood as well it seems.

but check first under the hood for burned fusable link. I don't think headlights have any other fuse.

Thanks for you input guys. I busted out the Haynes manual and looked at the wiring diagram and like andrew said a fusible link powers the head light switch and fuse block, the diagram said to follow the alternator wire back behind the engine, spark spark, Theres the problem, burnt fusible link. Disconnected the battery, Spliced a fusible link from the Dobas old harness and Shizzam! Im back in Business! Thanks again for your imput guys! I'm 18 so im still learning, and wiring isnt my hottest subject but i'd say i knocked this one out really easy. And to think i was about to take it to the shop.

You fixed the problem but you did not fix the cause. It has a 100 percent chance of burning that link up or worse if you did not use the correct fuse link.

the cause was a broken flasher arcing on the dash. Or a the horn relay was grounding on the dash because the fuse box was loose under the dash.