The resistor on the back of my headlamp switch is burnt out, which means I can't use low beam. Now I don't think I'll ever really have the need to use low beam since high beam is already low enough (!), but are these resistors available, or if not, does anyone know if a modern substitute can be used? From what I hear, the resistance has to be just right to ensure the correct headlamp power is achieved AND that the back of the switch doesn't get too hot.

Any advice?

Maybe someone could check the ohms on their resistor then Martin could get one and silver soldier it in.

Ask and you shall receive. Cold resistance is useless so you have to measure the resistor under load. According to my equipment, the resistor on my 28 coupe headlight switch drops 2.7 volts and the current through the circuit is 5.4 amps. According to Ohm's law, this works out to 0.5 ohms of resistance. The resistor also dissipates 14.6 watts of power which means it will get rather warm. If you wanted to replace with a modern equivalent, I would recommend a 0.5 ohm 30 watt resistor. You could connect two 1 ohm 20 watt resistors in parallel. (You want about 2x power rating as a safety margin).

Best regards,
Ron

I found this on Ebay:
40 watt 0.5 ohm resistor

Dan.

The resistor that Billy Barker uses in his replacement heater switches may be usable for the dimmer resistor in the pre 29 headlight switch, I have no knowledge of it's value and specs, but the function is probably close to what is needed to dim the headlights.

The ebay auction is for 30 units? If that is what it is then I think the winner should have enough. LOL

What a great bunch of Chev Nuts this group is! Thanks for all your help people, and especially to RustyFender for doing those measurements!

Post Script: A kind soul from NSW Australia emailed me privately to ask if I wanted him to go through his spare parts bucket to look for one of these original resistors. I have accidentally deleted the email, so if you are reading this, please get back in touch, as the answer is YES! Thanks.