The headlights on my 1999 Chev K1500 are acting funky. There are four headlights. Normally, I'll turn the low beams on and the two inside headlights come on and when I switch to highbeams all four headlights come on. Lately, when I switch to high beam, the outside headlights come on and the inside headlights go off. Low beam works fine (the inside headlights come on). Any ideas? Is it the headlight switch?