to get from the outer surface of the tail light bulb with original tail light housings on a bus up to 1971 to ground – the chassis, which is directly connected to the negative terminal on the battery. First, the ground current leaves the outer, round surface of the bulb and into the cylinder that surrounds it. That’s one interface. The cylinder is  crimped around it’s circumference to the the reflector/housing. That’s another interface. But there’s also a small tab at the  cylinder to housing interaface on the passenger side of the housing. The tab is riveted to the housing and may or may not be electrically welded to the bulb holding cylinder. Sometimes, it’s just pushes against it, dependent on a long term, rather high elastic limit (search this term on this site to understand it’s meaning) for long term, permanent pressure against the cylinder. It’s not even welded. The tab is there because VW didn’t trust the crimping as being a reliable current path, they felt the need for the tab. Without a weld on the tab, that’s an interface. With a welded tab, maybe – maybe not. Welds corrode and can make poor conductors. Tab into rivet – that’s another interface. Rivet into housing, another interface. Lucky current flow through lens mounting screw, another interface. A screw into the housing for an add on ground wire, another interface. Screw into crimp on connector on wire, another interface. From connector into wire, another interface. From wire into connector on other end of wire, another interface. From connector to screw screwed into body or chassis, another interface. From screw into chassis, another interface. If I counted right, that’s 12 interfaces and every one  of them can result in a no current flow and thus no ground and thus, poorly working tail lights. But the tab pressed against the cylinder can result in poor current flow and everything can look fine, but still – funky tail light/brake/turn signal function. But the other 11 can also contribute to bad lighting. But you can eliminate 9 (I think it’s nine, maybe eight. I’m too busy writing this stuff to bother worrying about that but you’ll get the picture and I’m still not getting any donations and this post is something you will find no other place but on this site and it’s golden. Punchline coming right after this)  of them simply by soldering the end of your ground wire right to the cylinder the bulb inserts into and soldering the connector at the end you attach to the chassis with a screw. Your lights will be brighter than when the vehicle was new. Make sure the bulb mounting cylinder is clean (electricity will not flow through corrosion or rust but don’t leap onto new fakes unless your originals are too far gone to save), along with the surface of the bulb. Use dielectric grease or anti-seize compound watered down with WD-40. You should be able to wiggle the bulb with your fingers while it’s on and it should not flicker while doing this. Now you know the bulb is really in right. You’ll never touch the bulbs again unless the bulb fails. And this is effective in many models of VW and many other places besides the bulb housings. Just think when you’re working. Inspect any electrical item you deal with – even if you’re trying to fix an original  6 volt  Ghia horn relay – for interfaces and use an ohm meter to determine their viability – zero ohms is what you want. Rivet? Maybe smashing it a bit (you gotta hit them hard to be effective so be careful of the surroundings) is an option for better contact. You can’t bypass them all but if you know where they are, you can really fix things. The fewer splices the better. Solder everything. Heat shrink tubing. Crimped connectors – take off the colored plastic if you do crimp so you can actually see your work. You can’t see through plastic. If a bulb  does fail and you get pulled over and the cop gives you a fix it ticket where you pay money because the bulb went out, start your own “Occupy General Electric” and refuse to pay the fine.  Tell the judge – why should you, dear reader, pay a fine, because the light bulb made by a huge, multi-national corporation failed?  It’s unethical for you to pay the fine.  If a fine is ethical at all, it’s General Electric that should be footing the bill.  We’re just innocent, victimized consumers. It really makes absolutely zero sense for anyone to pay a fine when a product they did not make fails. Do you get a fix-it ticket when you get a flat tire? Really, this is just wrong.