Classic cars forum & vehicle restoration.

[nqtraderman]

My car uses the pre focus dual filament headlamp bulbs and I'm thinking of upgrading it to Halogen bulbs. I know you can get a pre focus Halogen replacement bulb but they are 3x the price of a standard modern Halogen bulb.

Would a modern Halogen 3-pronged bulb fit into the back of the pre focus unit and secure with the spring clip ?

If so then it would then be an easy job to make up 3 spade terminals to connect it up.
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1954 Sunbeam Alpine

[Phil - Nottingham]

Only if you are very lucky - by definition the PF bulbs and the halogens have lugs to give exact focus ie postioning of the filaments to get best light output with galre/dzzle. It will be very unlikely they will swap over.

Old prewar lamps had to be manually adjusted to focus them each time a bulb was changed
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Phil

[MVPeters]

The quick answer is "No, they won't!".

Your original bulbs have a BPF base, circular with a small alignment indent.
More recent H4 halogens have a P4T (I think) base, larger & with 3 extended lugs. They won't interchange.
(By the way, BPF headlights don't have a spring clip, just a twist-on bayonet, so I'm wondering if your headlights are in fact original ones).

The easiest upgrade is the 'expensive' halogen BPF bulbs.
The alternative is to change the headlight units for either halogen sealed-beams or halogen bulb units - either way you'll need to change the BPF plug on the wiring harness for a 3-pronged one.

Hope this helps.
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Mike

[nqtraderman]

You're right. My headlamps have the twist plug at the back. I was going from memory thinking they had a spring clip.

Actually I never use the car in the dark, it won't get a lot of mileage on it in truth so I probably wouldn't get much benefit from halogens. I'll just stick with the pre focus bulbs .. and put the money I've saved towards fixing the overdrive oil leak

Thanks for the reply, your analysis was spot on and very helpful.
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1954 Sunbeam Alpine

[Jim.Walker]

I'm not sure whether we are talking 6 or 12 Volt here. But 6volt British Pre-Focus (BPF) halogen bulbs are well worth the expense in my book.
I have one fitted in my 1959 6volt Triumph motorbike and the improvement is tremendous. Easily comparable with a normal 12volt bulb output.
I can't say how much improvement it would make on 12volts. But if you are on 12volts it might be better to consider changing your BPF light units to halogen types. The 12volt Wipac Quadoptics fitted to my car are amazing compared with the old Lucas BPF type units.
Jim.
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Quote from my late Dad:- You only need a woman and a car and you have all the problems you
are ever likely to want". Computers had not been invented then!