[Doctor john]

When restoring the dash in my 1967 LeMans, I replaced the dash harness and turn signal switch. The front, rear, and intermediate harnesses were replaced within the last couple of years. Everything works well but I noticed that the front parking/turn signal lights turn off when headlights are turned on. They work fine as turn signal and emergency flashers and as parking lights, but when the switch is pulled to turn on headlights they go out. Is this how they are supposed to work? If not, what could be the problem? I was going to check the bulbs to see if they are single or double filament.