hi tail gate bulb keeps blowing as soon as new one fitted 2007hse

Does this happen immediately, within a second or so? Another member of the failed FL2 clutch/DMF club, twice.

yes it dose

One of two things I think.
A short circuit in the cable feed to the lamp or the lampholder itself, and as the current rapidly increases and finds it's way to ground, the filament acts as a 'fuse' so to speak.
This could take some finding!
Less likely is a bad batch of bulbs, but I've only ever seen this once. Another member of the failed FL2 clutch/DMF club, twice.

Well if they are 12v bulbs (and not 6v motorcycle ones) they can't be getting more than 12v from the battery so I would test the bulbs by putting them directly across the battery. If they were taking too much current the fuse would blow. Check the bulbs are OK, previous comment about rapid current increase is highly unlikely.

The CHMSL lamp (Centre High Mounted Stop Lamp) is a 16W filament.
Therefore, in normal conditions it will draw 1.3A. In addition the rear two stop lamps are 21W. Add it all together and you get 4.8A. The circuit is protected by a 5A fuse, bit to low to my liking but nevertheless a 5A fuse will withstand 135% of its current rating for ever and a day to cope with transient peaks and spikes. A filament bulb cannot draw anymore current than it's rated wattage.
The fuse is there to protect the wiring, not the bit on the end, in this case the bulb.
A short circuit can draw a huge amount of current, even a 0.5mm cable with a 5A fuse can draw 100A or so and will rupture the fuse within a few m/s.
The weak link here is the filament, it wont withstand the fast inrush of current in a short circuit situation to ground as a 5A fuse.

In addition, never ever attach anything direct to a car battery without a fuse in parallel unless you want acid all over your face! You could end up looking like Wayne Rooney. Another member of the failed FL2 clutch/DMF club, twice.

The bulb wattage determines the current draw. A short circuit before the bulb on the feed side would stop the bulb illuminating. A short on the earth side would make no difference.

Yes, that's what normally happens
But if the filament keeps on rupturing, it can only be caused by overload from somewhere.
Unless something daft like shock to the filament during fitting........... Another member of the failed FL2 clutch/DMF club, twice.

thank you for replies