Somehow I will bet you have electrical grounds that need a good cleaning
So many electrical things come back to life just doing that
i think you might have some idea what’s going on —being real good with the electrical end of our cars
Clean the negative ground of the battery --to the cars frame located under the battery tray
Polish the metal until shinny and clean at all contacts
You will need to remove the battery to get to that connection
Remove both battery terminals and clean them Good
They make a wire brush tool just to clean the terminals
Check the batteries fluid if it is possible with your kind of battery
Add Distilled water to top it off
The battery and alternator are the source of all power to the car so a good place to start
Clean the negative ground and all terminal ends --of the regulator behind the fire wall on the passenger side
Do all electrical cleaning with the negative terminal OFF the battery
Grounds as Tony recommended. After that, there is an overload to the circuit breaker on the headlight switch. Inspect the dimmer switch electrical prongs for heat damage. The connector to the high beam may be loose, causing heat/excessive draw to the wire, or shorting out.
Replace the dimmer switch and use new electrical connectors. If it still does it, a wire may be damaged, causing an overload.
After that, I recommend my relay wire harness. It uses 2 relays to directly connect the battery to the headlights. The headlight switch acts as the trigger to the relays, so vert little current draw goes through the headlight switch.
Best of all, there is no cutting or splicing of wires. The relay wire harness plugs right into the stock headlight plug. They are 70.00 each.
Jake, the main ground you want to check is the forward lamp harness grounds that feeds the headlights, cornering light, park lights, and turn signal indicator. If they are not making good contact the lights will often flicker and appear dim, and usually not just go completely out on both side, ... but, in terms of grounds that is the main one you want to check. The forward lamp harness comes through large grommet on the radiator support to the bottom left and right of the radiator, then a black wire connects to the frame as seen below. These are prone to corroding and/or becoming loose with 50+ years exposed to the elements.
The Forward Lamp Harness grounds are easy to check so that is why you start with them. My next guess would be a faulty headlight switch. Perhaps the Circuit breaker or other contacts on the inside of the switch are corroded, shorting or not making connection. If you don't have the switch out of the car yet you can see the illustration in Fig 12-2 on page 12-4 of your 1963 Cadillac Shop Manual. I don't have any 63 switches on hand but if memory serves you can open up the casing and check the contacts inside the switch. If you need a switch it sounds like Russ has what you need.
Yep, they fall into many pieces.. little springs and such if memory serves. You need to be prepared if you plan to open one up. That is why a good replacement switch from Russ or someone might be a good option if you are in a pinch for time.
The 63 headlight switch is a walk in the park, compared to the tilt wheel turn signal switch. I would like to sit in a small white room with no floor drains, no furniture, nothing on the floor.
Whenever I do a headlight switch or tilt turn signal switch, I take it apart in a deep shoe box. If anything goes flying, I have a much better chance at recovery.
I did a carb once (looong time ago now) off some old piece of crap. I thought I had everything going well and I tipped it up and my balls fell out on the floor. :-(
Bloody hell, chasing two little tiny shiny balls to every corner of the friggin workshop floor.
Found 'em too.... wasn't easy and never fell for that drama ever again.
In Jasons second picture you can see how bad some grounds can get after being 50 plus years old
The boys here will get you fixed so just check off one thing at a time that is suggested
You are in expert hands with the subject of our cars-- on this site