Are you sure itís the front park lights and not the front signal lights coming on when the brake is applied? Iíd first recommend you double check this. The front park lights are not tied into Eng. Edís duel brake/turn light circuit. His internal circuits for the park and main headlights are completely separate. It would make more sense if the front turn signal lights were coming on as they are tied into Edís turn circuitry.
If youíve double checked the wiring and think you have it right, Iíd check if the problem is in the Black box wiring or your connections to the black box. To do this, get a 12 Volt power source. I use my trickle charger (allows for me to play with the circuits inside the house), but if you donít have one, use a 12 volt battery. Hook the negative terminal to Engineer Edís ground wire. Now take the positive feed and connect it to the wire identified as the brake light feed. You should here the two relayís click. Now you should have power to the output wiring going to your rear brake and signal wiring (only these feeds out of the black box should be live). Take your volt meter and with your negative hooked to the negative terminal of the battery (or charger) and test the wires designated for your rear brake and signal outputs. They should be live. Now hereís the clincher, check the wire coming out of the box, intended for the park lights. If that wire is not live, then the black box is working as intended and you need to re-look at your wiring to and from the box. If it is live, then itís something to do with the black box.
Assuming the B Box is working correctly, check the two wires coming out that are intended to go to the rear brake and signal lights (make sure theyíre clearly marked with tape or something so you donít get them mixed up). One of those wires is connected to your park light circuit OR when your brake switch is closed, youíre also feeding power to the park light input connection to the black box. If I remember correctly, my 91 harness the park light wiring was all brown. It should be easy to determine which of these wires is connected in some way to that circuit. If youíre sure itís not, then check the feed going to the park lights, to see if it goes hot when you apply the brake (it shouldnít, if it does, this is your problem).
I canít see it being anything other than these few areas. Write back if you find something unusual after completing these checks.
P.S. Sounds like you are, but make sure you have and are using the wiring diagrams specific to the 93 harness.