Testing headlights for right voltage?

Best way is to measure the voltage *drop* on both positive and negative.

Set the DVM to 2 volts and measure between live on the bulb and positive on the battery. Do the same between ground and battery negative. Something like no more than 0.2 volts would be ok.

You could start by cleaning all connections, switches and relays in the path. However, if the voltage drop on both positive and negative is similar, it's unlikely to be the cause.

And higher powered bulbs will show more voltage drop.

Might just be easier to fit a new 30 amp cable (via a fuse) direct from the battery to the lights and use a couple of relays to switch from the original circuit.

The message from Alan Simpson < > contains these words:

I very much doubt this is the problem, but if you want to test it, check the voltage across the back of the bulb (with the bulb in circuit) and compare to the voltage across the battery (with the same lights on). You shouldn't see more than half a volt or so difference.

I would be inclined to check the reflective lining of the headlamp for signs of going dull. It has been known to happen on cars of this age, or earlier for that matter.

PDH

The message from "Paul Hubbard" contains these words:

Bother - that was the bit I /meant/ to write after the "I very much doubt this is the problem" bit!

There is in my case, it's called a Bakers Cyst. DaveK.

The message from "Dave Plowman (News)" contains these words:

There is - it's your popliteal fossa.

I do recall seeing a headlight unit once that was doing a very good impression of a goldfish bowl. :o(

PDH

Have you been listening to Viv Stanshall again? I warned you about that.

The dim dip circuit could be the problem. This puts the dip beam on at reduced voltage if the ignition and sidelights are on. Don't beleive me? Take the front sidelight bulb out and see. You would not believe how many cars I have seen pass the MoT with blown sidelight bulbs because the inspector tested them with the ignition on.