Headlights quit working on my son's 88 Ranger. Had been an intermittent problem before which he says cycling the dimmer switch would usually cure. Sometimes right away, others not(after about 10 minutes would). No joy this time. Checked fuse which was good. Checked connections at lights. A little corroded, cleaned. Wires seem a bit bit loose in connector but still making good contact. Searched forums, saw some problems with connectors, light switch, and or dimmer switch. Any way to isolate to one or the other. Don't have my haynes manual readily available so no wiring diagram to work with. Is there a relay in this system? Truck is stock. Was mine since new until I gave to my son. Thnx for any help.