If you are using all led bulbs, check the polarity . Led bulbs will only work in one position . Quick test, take out one of the bulbs and hold the leads from a 12 volt source to the contacts of the bulb. It will only light if the polarity is correct. That will help you identify which contact on the bulb is positive or negative.
Also, I agree with above comments about poor ground. Common cause of this problem.
