Headlamp on high beam..
 

The left headlamp does not come on unlike the right on high beam. But after revving, it comes on right after. Low beams are all right though. Where could the problem come from? Your input would help a lot. Thanks.

Your plug connectors are corroded. When you rev the engine the increase in amperage overcomes the resistance in the connectors. Unplug each one and spray with electrial terminal cleaner.