Techtip21

SAVVA Technical Tips No 21

Replacement bulbs

Many of us own vehicles manufactured some years back when headlight bulbs were of
wattage of around 60/40. Most American cars went to seal beams in the late 50’s but
many English and Continental cars stayed with bulbs into the early 60’s. Today headlights
with bulbs are not only rather useless but also possibly illegal when it comes to C.O.R.’s.
If you use your vehicle in the evenings and have developed a phobia about the lack of
illumination, and, added to your concern, the current lack of painted lines on the roads
consider upgrading the wattage of the light bulbs, or if possible, fit seal beams.

I scratched around the shelves of the local Midas parts store to see if there was a
stronger wattage bulb that I could use in a 1960 Bentley which was fitted with 60/40’s.
I found there was a QH (quartz halogen) bulb available that fits into the original Lucas
fitting that increases the wattage to 100/90 – a vast improvement, and only R35.00 a bulb.
Apart from the increase in wattage the lights now have a clearer beam rather than the older
yellowish one.

I also have a 1935 Buick that had very ineffective 6-volt bulbs. Here I did what many
purists would consider unthinkable and fitted 6-volt seal beams – problem solved. I can
now use this car in the evenings.
Many owners have converted their 6-volt systems to 12 volt hoping to improve the lighting.
Unfortunately this change over won’t help, as the voltage used on the bulbs has nothing to
do with the final illumination. (Unless of course if the wiring is too thin) Whether you
use 6, 12 or 24volts, what counts is the wattage rating of the bulb. Therefore a bulb rated at
100 watts will give the same illumination on 6,12 or 24 volts.

Whether you have fitted upgraded bulbs or not, may we also suggest you take a voltmeter and check
the voltage at the bulbs terminals. So often, especially with older wiring the plug-in contacts or
the light switch contacts are worn or dirty reducing the voltage to the bulbs quite considerably.

In many cases, especially with six volt systems, cars have been rewired with wire too thin for
the voltage. Keep in mind, every time you half the voltage you have to double the wire size.
A six volt system therefore requires a wire size double that of 12 volt. If you find the wiring
is too light with a resulting a voltage drop at the bulb the only answer is to double the wire
size or fit a headlight relay.

Eric