Diagnosing Dodgy Headlight

[number49]

Hi all,

Mazda 3, 57 Plate (2007/2008) 1.6D TS2

I have had a problem with the drivers side headlight. The bulb 'went', was replaced and was ok for a night or two then 'went' again. It is a normal H7 type bulb (NOT Xenon/HID's)

All other lights are working ok so would assume it's not a fuse.

I have just inspected the bulb and compared it to a new one and there is no obvious blow. I then tried the new one and the light still isn't working.

What basic steps can I take to diagnose the fault? ( I should be able to borrow a multi meter if needed)

I suspect either the bulb holder or cable to be the cluprit but have no real experience with car electrics.

Any advice welcome.

Cheers,

Mike

 

[Mursal]

To test, connect the suspect bulb across the terminals of a good 12volt battery. One terminal to the body of the bulb, the other terminal to the wire. Doesn't matter what way round you connect.
If it works and it doesn't in the car, you have a fuse blown (dedicated fuse for that light) or a bad connection. Try the fuse box should have the fuses labelled? And/or wiggle the wires going into the light unit with the lights turned on, it may start to work. Might need to leave the car running, or it wont start.

Good luck

PS
The Multimeter will be plan B .......

 

[Belle427]

turn on the lights and give the connections a wiggle, you can also remove the connector to check for corrosion on the terminals.

 

[number49]

Cheers for the replies. Will give them a try.

 

[number49]

I've found the dodgy connection, the bulbholder is corroded/melted and cleaning/scraping the terminals has got the light working for now...

Before I replace the bulbholder I want to know what causes the damage and how do I stop it from damaging the new one? Is it just wear&tear or is there likely to be a fault?

 

[Mursal]

New one will probably last the life of the car, but usually loose connection causes heat and therefore melt. Not to get to technical. the current flow is quite high to the bulb, so any looseness/corrosion will generate heat.

As long as you found the fault, happy days

PS
A local breaker might have one?

 

[TicklyT]

An initially slightly dodgy electrical connection may tend to overheat, causing oxidation on the contacts, leading to a poor connection, more overheating, more oxidation and failure.

Make sure the contacts are bright metal, clean and dry on assembly.

Address any obvious signs of water ingress.

Some (many?) advocate lightly greasing the electrical contacts with petroleum jelly on assembly to mitigate the effects of condensation causing oxidation, but that may be of little benefit for headlamp connectors, as the lamps get hot.