Mustang II Member
Joined: May 2008
The wiring makes an L from the firewall down the drivers side and across the front to both headlamps. It really could not be switched around. Most likely with old wiring you either have bad/loose/corroded connections or some wiring is split or missing insulation.
You can pull the connectors off and spray brake cleaner into them to clean them really well then make sure they are good and dry. Buy some di-electric grease from any auto parts store and put some in each of the connector holes then plug it back in after checking to make sure none of the connectors are bent or broken. That should help with your dim lights unless one of the bulbs is just worn out which did happen with those old glass single beam lights. Try swapping the headlamp bulbs and see if the same one stays dim then you will know. It is a cheap and easy way to give you safer and more reliable connections as it also waterproofs them.
1964-1/2 Mustang 260 Conv, 1966 Mustang 289 Coupe, both projects
2001 F-150 Lariat for daily use.