Where is the negative side of coil on ford f100 with a 3.8 motor

If you look closely at the coil it should be marked with a + and a -.

Are you sure that it is a 3.8 l engine first of all second what type of coil is it the old style canister or the newer style HEI type I ask because if it is the canister type on all the ones I have delt with red was pos and black was neg now on the newer style the coil is designed to have to hot leads one constant and one pulse the distbutor tells the coil when to send the pulse to it hence the little ignition box on the distibutor, I have a 1986 with the 300 i6 and had run into a problem where I changed the coil the dist. And that finikey little ig box on the dist. Now I suggest that being u have an older f series ford go to ur Napa carquest or any auto parts store and get the tool made for the two nasty little basterds that hold the ig box to the side of the dist.