Picked up John Sneddon's excellent book on Australian built Minis. One thing I noticed is that the Lucas headlamps were upgraded in Oct 1969 from 60/45W to 70/55W. How can you tell the difference? I have some spare used Lucas sealed beam lamps and can't find anything obvious that identifies whether they are the 60/45's or 70/55's

_________________
1970 Cooper S SPO41

If there is no ink stamp on the back then you could use Ohms Law to work it out. You just need to measure your ohms readings.
http://www.bowdenshobbycircuits.info/ohmslaw.htm

Thanks, had forgotten my high school physics

_________________
1970 Cooper S SPO41

Right logic, but the cold resistance that you might measure with a multimeter will appear to be much less than the hot resistance (about 2 ohms) when the wire is carrying 5 or 6 amps at 60 to 75 watts. This is also why most bulbs "blow" at switch on when current is much higher for the first fraction of a second.
A more accurate method would be to connect the light to a car battery and measure the current (if your multimeter has a 10 amp setting). 5 amps => 60 watts and 6+ amps => 75 watts
Don't leave the multimeter connected for more than a few seconds as 5 or 6 amps might heat it up.
Dave D

Thanks Dave

Sent from my SM-A305YN using Tapatalk

_________________
1970 Cooper S SPO41

pdpsing
I dug out two old Lucas sealed beam headlights and measured currents.
60/45 was 4.2 amps at 12.2 volts on highbeam and 2.6 amps at 12.3 volts on low.
?/? was 4.9 amps at 12.0 volts and 2.9 amps at 12.3 volts ( did not see brightness difference)
The ?/? did have very dirty markings until I tried to wipe them..... bad idea.
The 60/45 calculates at well below 60 Watts but I assume it is meant to have 13-14 volts in a running car, not 12.2 volts from an Aldi deep cycle.
The cold resistances were about 0.5 ohms but multimeters were just guessing this low.

Thanks Dave. Bought a multimeter this morning so I can test mine

Sent from my SM-A305YN using Tapatalk

_________________
1970 Cooper S SPO41