Just installed a new starter in friend's regal 3.8, and hooked all wiring up to it, then the battery, and the car doesnt seem to get any power exept the headlights and the horn.... Fuses inside and in the engine bay check out ok... what could the problem be?

Would it be that hard to include the year of the car?

If you put the old starter on does it work again. Could be a bad starter or you installed the wires wrong or left a wire off.