Hi beam stay on

This could be a faulty relay or a failed headlight dimmer switch. The relay in question should be in the power distribution box under the hood. The cover of this box should identify the headlight relay(s). Pull out the relay or relays in question. If the part numbers are the same as on another relay, such as the air conditioning relay, a quick basic test is to swap them. If the problem moves to the other system when the relays are swapped, it is 99% sure that the relay is faulty. If there is no identical relay to swap, a proper test is to briefly apply battery voltage to the two control (usually smaller) pins of the relay. If the relay clicks, then it is probably good. To be certain, you can use a multimeter to check for a connection or "short" across the two power (larger) pins of the relay. When voltage is applied to the control pins, the meter should beep or light up to indicate contact on the power pins. If unclear about which pins are which, note that most relays will have a diagram printed on the side to indicate which numbered pins perform which function. In this diagram, the coil graphic is for the control side, and the broken, angled line with an arrow is the power side. Whatever you do, do not keep voltage on the relay for very long, and if it starts to get hot, disconnect immediately. If the relay(s) check out OK, it almost has to be the dimmer switch.