Are the last 4 lights on a ckt of there own or are there other lights in that string. If there are others, remove the bulbs and see what that does to the voltage. LED s will cut the current by a third, remove 3 of the 4 bulbs and check your voltage. If it is only the 4 bulbs you can use a buck-boost transformer wired as a transformer not autoformer. Use a 16/32 vmodel (sized for the load) wire it up 16 v sec. the only problem with this approach is is each bulb burns out it will increase the voltage to the remaining bulbs. causing them to fail early. Best solution is a bigger feeder (ga) or lower current lamps (LED)
