Converting Headlights to H4 Halogens
by Ulf Nyman
All this talk about Sealed Beams, H4 and their predecessor that we Europeans call "plain old headlight bulb" makes me remind you all about VOLTAGE. When I upgraded my 1971 Kombi to H4's I happened to measure the voltage at the bulb's socket. It was just under 10 Volts. If you look at the scheme for your VW you can understand why.
Let's follow the funny ways of the plus lead, starting at the battery pole going to the starter motor, the fuse block, light switch, relay and finally to the light bulb (I probably forgot one or two). Every connection lowers the voltage a bit, especially when the electrical system is getting old. All bay window busses are old by now. :-) Ok, ok not the Mexican and Brazilian ones....
The remedy is a bypass operation. A new heavy gauge cable from the battery (put an inline fuse near the battery) to the dashboard ending up in two new relays, one for short beam and one for long beam. The old system operates the relays. Put in new cables and bulb sockets and WOW, what a difference! Two or three volts makes a big difference in light power. Let's do the math.......
This is what we should have:
The Voltage should be about 13 Volts.
The resistance in the bulb about 2.8 Ohms.
The current is then 4.2 Amperes.
This gives about 55 Watts.
This is what my '71 Kombi had:
9.6 Volts.
The resistance is relatively constant at 2.8 Ohms.
This gives a current at 3.4 Amperes
And a power of 32.6 Watts
55 Watts instead of 32.6 is a 41 % improvement! This, plus the H4 upgrade allowed me to use sunglasses anytime ;-)
Schematic for New Wiring and Relays:
Al Brase writes:
I agree that these are a great way to improve nighttime vision. I had a set of these (Brazilian Hella, I think) clear back in the 80's and they were great. Two caveats however:
1. They don't have the alignment bumps on them that sealed beams have, thus necessitating manual alignment.
2. They do, over time, get tarnished inside in the silvering. I used mine for 7 or 8 years and could definitely see some degradation inside. This is why they are not DOT legal [in the US] and what DOT is protecting us from by making us use sealed beams. Sealed beams are mediocre, but at least they won't get worse! I'm sure they could be taken apart and resilvered, like the lights on your 1934 Duesenburg J, but it might be cheaper to buy another set for spares in a few years.
[Editor's Aside: Unca Joel Walker once noted improved headlight intensity on his older Vanagon after extending a fresh, heavy gauge ground cable from the battery directly to the grounds on the headlamps.]
