Well, I don't have any 7806 chips handy (to output 6v) but I do have one of the voltage regulators I made (adjustable). The Runtz device used the 7808 simply because your generator will provide 7 to 7.2v through your voltage regulator so your gas gauge won't see 6v...but a lot of folks don't know that or maybe they do know it but they don't always remember. Important...it won't output 6v unless something is wrong with it. Runtz used the 7808 chip because it was cheap, 8v is close to 7.2v and they didn't want to make an adjustable gizmo. There is no LM7807 chip...not a popular voltage choice. If your 6v gauge has not been exposed to 12v it may not have been re-magnetized and if that is the case voltage may make a bit of difference...it also depends on how the electromagnets in your gauge were wound (a complicated swamp we're going to avoid today). Explaining the variables of electromagnetism can head into deep water quickly.
If your needle moves correctly and through the entire range and your sending unit is good for 0 to 30 ohms, you can (a) fill your tank (b) disconnect your battery (c) install the device I made (which installs just like the Runtz thing) and (d) carefully adjust it using a tiny screwdriver until your gauge reads F. Tip: you can connect a wire or patch cable to the fuel gauge and then to the device I made so you can do this without having to crawl under the dash and then install it after you've adjusted things. You will need to connect it to the power wire going to the gauge using the thumbscrew connection, connect it to ground (using the black wire and connector) and then connect it back to the gauge using the patch wire (connect to the back side of the device and then connect the patch wire to the correct gauge post). I can't offer anything for sale on this forum, but if you'll please send me a PM I can tell you more. There are some images below that explain this a bit...
~ Jon 1952 1/2 ton with 1959 235 | T5 with 3.07 rear end
