I recently extended an existing 20 amp/12g home circuit by tapping into an end-run duplex outlet and installed two new exterior wall lights controlled by a digital timer-switch. The additional length of wire is 30 feet. The bulbs in the new lights pulse and flicker continuously and eventually burn out much faster than normal. I have tried different types and wattages of bulbs but the result is always the same. Most of this circuit is seldom-used and holds only normal-use receptacles and ceiling lights. There is no problem with any of the other bulbs in the run. What could the problem be?