Brake lights 65 vw beetle

[Windsurfa1]

My brake lights work fine during the day. When I drive at night , and turn on my headlights. My brake lights dont come on, though my headlights and running lights , signal lights all work!! 12v converted.

[GArBa]

easiest explanation: bulbs wired incorrectly or wrong bulb used in the socket so that the brake lights are fed back 12V from ground when the headlights are on.
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cars:
'97 type 1 1600i
'14 type AA Seat Mii (sadly dead after 270.000 km)
'22 type C1 T-Cross
'23 type AC3 Hyundai I10 (VW no longer makes small cars!)
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moped:
'82 Benelli Magnum 3v

[ashman40]

I believe in '65 the taillight assemblies grounded thru the fenders and then thru the fender bolts. This grounding connection is notorious for causing trouble as the connections start to corrode/rust. What is likely happening is your brake lights are grounding backward thru the parking light circuit. While the parking lights are OFF the different bulbs in the circuit provide multiple paths to ground. If your taillights have a bad ground the current will prefer the path thru the parking lights. When you turn on the parking lights the brake bulbs loose their path to ground and stop working.

TEST: Remove the taillight lens covers and with a jumper wire (a jumper wire with alligator clips will be easiest) ground the metal body of the light assembly to a known good ground point. Test your brake lights with and without the parking lights on. They should work as expected. This confirms your taillight housing ground is bad.
Fix is to run a dedicated ground wire. Affix one end to the metal body of the light assembly and run the wire into the engine compartment along with the three other wires. Ground the other end to the side of the engine compartment with a sheetmetal screw. If you don't like the idea of adding holes in the body of the car, run the wire to an existing ground point. Just make sure it is clean and provides a low resistance path to ground out of the elements. Coat the ground point in dielectric grease to protect it from corrosion.
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AshMan40
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'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[KTPhil]