V8 250 saloon: headlight problems- please help

[sidfish]

Hello all

I hope everyone had a happy Christmas!

I am experiencing a curious and somewhat inexplicable issue with the headlights of my V8 250 saloon. When I start her up, the lights work fine but occasionally, after I park up, turn the lights and car off, and I start her up again, the headlights are dark and don't turn on. All other lights work perfectly. This has happened twice now and I have had to make my way home using the fog lights instead of the headlights.

The last time it happened was on Christmas day and I have not taken her out since - but what sometimes happens is that after a spell when i start her up again, the lights work as usual. Sometimes they remain dark. I would assume there is a loose wire somewhere but I don't know why as I recently tightened the connections.

Any advice would be warmly appreciated. Thank you and I wish you all a merry New Year!

All the best
Raul

[captain bobo]

I had a similar intermittent problem about 5 years ago which turned out to be faulty innards in the rotary light switch.

[Christopher Storey]

Either that, or perhaps even more likely, a faulty earth in the circuit

[sidfish]

Thanks for the replies! The switch is relatively new but I will check the earthing and if this does not work I will look to getting a new switch (again!).

All the best in the New Year

[tjt77]

hard to diagnose without actually looking at the car, but none of this is rocket science.. and very simple tools can help with diagnosis..you need a simple 'test lamp' to confirm power is flowing.
there are 3 common issues that may be the cause of you problems :- (1) poor ground or 'earth' connection between lamp unit and cars chassis.. (2) failing dipswitch ( quite common after 50 yrs of use) (3) failing rotary switch ( not common..but it does happen) firstly take a 'test lamp' with one side grounded, and check to see if you have power going to the block on inner wing where the bullet connector to lamp connects into the wiring loom after truing the lights on.... IF you have power there, than remove the headlamp and check that the power is making the final leg of its journey to actual bulb holder.. IF it does have power there. the most likely issue is a poor earth or ground..
no power at the connection block indicates the problem is elsewhere.. in which case, proceed to the actual switch and test for power there. The most common issue is generally corrosion in the bullet connectors.. or the plated brass holder that is bolted to inner wing to complete the circuit.. these can be cleaned out with an 'engine gallery brush'.. long and narrow wire brush designed for getting into smell holes.. generally if the dipswitch has 'issues' it will reveal itself when you dip the lamps and should be fairly obvious.. Im unsure if anyone else recommends applying WD40 to older switches, but I do and have been doing so far several decades in order to help older switches continue to operate .. as they get old they get crud build up and can stick.. a little lube helps resolve this issue.. id say that the majority of issue are a direct result of poor earth or found.. these are what tend to fail 1st..and its usually the connection between receptacle and cars body corrroding and creating too much resistance to allow current to flow through.. BTW.. ground or 'earth' wires are almost always black .. whereas 'power' wires for headlamps are blue with a tracer colour for high beam and dip.. good luck.

[sidfish]

Thank you very much. I have copied your excellent step-by-step guide to diagnosing the problem and printed it to make sure I have it offline. This is so incredibly useful, especially as I am just getting acquainted with doing more of the work myself.

Thanks again!

Raul