Tail Light Bulb keeps blowing

[Littlegun]

Hi Guys,
The RHS rear Tail light bulb keeps blowing, just the running light part of the bulb, not the stop light part.
It must be getting too hot as the plastic divider in the tail light housing, looks like it has melted.
Have replaced it with a NARVA brand,the rating numbers matched.
I was on my 3rd when it blew this morning.
Has anyone had this problem

Regards Rob

[glend]

Sounds like you have a short in the wiring to that lamp somewhere. The BCM (Body Control Module) sends power to that running light. There is a wiring diagram in the Service Manual, Section 8 I believe, might be worth having a look to see where it goes from and to to find the problem. If you can't be bothered then consider an auto electrician.

[Pipeliner]

A short will blow the fuse, not the bulb. Bulbs usually only blow like that if the voltage is too high - possibly the voltage regulator on the alternator has died, allowing the full alternator voltage to be applied to the circuits. Although why that would affect only one bulb is beyond me.

Have a probe around with a voltmeter, both with the engine running and not running, and see if the voltage is significantly different between them.

Totally off topic, I once had an alternator regulator fail completely in a Ford Transit coming from Poland to UK (in 1970) - wouldn't charge the battery at all, so we bypassed it in order to keep going. When we arrived in the UK the pitch sealing the top of the battery has boiled and the lead plates inside were warped and distorted - but it still started the engine!

[glend]

Guess I should have been more clear. The power to the rear lights is shown in diagram 8W-51 in the Service Manual. The power is supplied via a power relay and fuse, but more than one lamp share that fuse. My suggestion of a short meant a short to another power source which would be only affecting the wire to the right rear lamp probably after the junction block. I share Pipes view that something else should be affected as well.

[coopers]

Assume you have a tow bar fitted? Have a look at where the trailer electrics are spliced into the lume.

Do you have electric brakes? Have a look at the controller wiring.

Also, a long shot, but check that no wires are hanging down under the rear bumper onto the exhaust tip. My lights were shorting out and found the insulation on the wiring to the trailer socket had melted/worn through on the exhaust.

[Escapable]

Firstly, I am with Pipeliner on the voltage problem.
If there is a short to something else, this will still be only the supply voltage and may blow a fuse elsewhere, but not the bulb.
First thing to check is that when we change bulbls we tend to copy the original... it should be a 6w bulb or if it is a como with the Brake light a 21W (brake) and 6W (tail). Note that the 6W should not be melting anything altho the 21 may if on for long periods.
Overvoltage can only be caused by the alternator giving too much voltage, this could be caused by dirty or corroded battery connections and terminals, thus tricking the PCM into forcing the alternator to give more - this would be evident by corrosion on the terminals and even around the battery compartment itself.
Is it a replacement alternator and if so is it internally regulated?
Are there any other electrical problems (dash blacking out/resetting?)
Best to clean the terminals completely, both the connections and posts using emery paper.
This can of course be tested with a meter on the terminal posts (NOT the connections) and then onto the connections - these readings should be EXACTLY the same, noting use of a digital meter AND with the headlights on high beam.
Note also that this voltage should would be considered high at 14V or so and would be a case of dying battery although I would assume some starting problems?