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There are others in there with similar symptons - ie, it fixing itself on toggling the lights.

You can see it really clearly if you use the dimmer when in the car. It's really erratic and will jump up and down in brightness if you don't have the cap added.

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I'll give the cap a shot. Cheers for pointing me in the right direction

If you're reasonably good at soldering then it's no problem to do. The major worry is damaging the VFD or the fill nipple on the side. Make sure you don't damage that and it's a breeze.