Brightening the Headlights

[Colin Morgan]

Looking at my Ruby headlights today, they do not seem as bright as they used to be.  The system is the original 6v positive earth set up - dynamo and cut-out - with the common 1950s 7" Lucas reflectors fitted and wiring altered to suit dipping of both.  The battery and reflectors are in good condition, so I suspect the voltage reaching the bulbs is not what it was.  I plan to have a go at cleaning up the various contacts on the live and earth side, but is there anything else that might help, please?

[GK5268]

The light output from a bulb will decay as it ages, just fitting brand-new bulbs may restore their brilliance.

[Mixer]

Hi Colin
Have you checked the voltage at the bulb? for a healthy circuit there should be hardly any drop in voltage.  You would find a distinct difference in upgrading to LED's, easily 100% brighter as long as your reflectors are doing there job properly.I was amazed at the difference front and back, well worth the outlay if you are doing a lot of night driving.You can always pop the normal bulbs back in for the purists. cheers.

[Renaud]

Hi Colin,
About the earth side of things, a good indication of wealth is to measure with a voltmeter between the positive of the battery and the earth side of the lamp while lighted of course. It should be zero volts in an ideal world but I'd say that more than 0.5 V would be an indication of poor earth somewhere. That can be then traced back from the battery plus to other earths.
The same can be done on the minus side evidently.
Sorry if what I said is obvious!
Hope that helps anyway.

[Ian McGowan]

Hi Colin I would switch on the headlights with the engine stopped, measure accurately the voltage at the battery terminals and then at the bulb contacts on each headlight. There will be some voltage drop, if this is significant, I would then work through the lighting circuit from the battery towards the bulbs measuring the voltage at every accessible point. This should enable you to identify the point of significant voltage drop, if there is one and allow you to address that issue first.
It is possible of course, that your battery is tired, or if you have one, that the battery isolator switch is introducing resistance into the circuit - check the voltage drop, under load, across this switch as a first job. It can go faulty and it has happened to me once.

[Colin Morgan]

Thanks - I will do a few checks with a voltmeter and see how it all looks...

[John Cornforth]

Hi Colin

The headlight current returns via the metal of the body/chassis, via any bolted joints such as the front wings.  Since the earthy side of the battery normally connects to the engine block (at or near the starter motor) there must also be a link to join the engine block to the body.  With a rubber mounted engine this link may only be provided by the copper petrol pipe and the bolts holding the tank to the chassis. Many owners fit an additional braided strap between engine block and body, or fit a lug midway along the earthy starter cable and bolt it to the battery/tool box.

As others have said, using a voltmeter across any switch, joint or junction will show up excessive voltage drop when the circuit is switched on.  I would aim for less that 0.6 volts total drop in the entire feed and return circuits, i.e. less than 10% of battery volts.

[Bill Dixon]

One item often missed is the dip switch.

[Stuart Giles]

A simple way to see whether you have an earthing issue is to temporarily connect a decent size wire directly to the battery earth connection; then touch the end of the wire to the headlight when it's switched on. If there's a noticeable improvement in the light output, the existing earthing arrangement would benefit from looking at.

Although I have a 12v system on my special, I have the headlights' earth connection cabled directly back to the chassis, the mechanical connection has a smear of dielectric grease on it.

[andrew34ruby]

Brightness of headlights while driving is not affected by the battery, but is very much affected by the charging system. Checking voltages and volt drop with a meter is good, but is best done with the engine at a fast tickover.