Unfortunately we are going around in circles. I already gave the same info that was linked by Andy. It's not readily apparent however. I will try this approach. A linear voltage regulator can be purchased for $1-$1.5. The kind I'm speaking of comes in several "packages". The one I mentioned and supplied a pic is a TO-220 (Japan), they also come in TO-39 (Texas instruments) and TO-252 D-PAK (Motorola). These are just bodies and connection variances. All surface mount. The actual IC inside is made by various companies and packaged into the "body" with "permission". TO= Transistor Outline (package). D-PAK= DECAWAT PACKAGE.
The point is that Runtz is a 3 pin linear voltage regulator IC in a usable package. It was designed to be a DIY user friendly install. With all due respect, it was over designed. It is obsolete. This is a small issue with a giant blog. Of which I am participating in, due to Covid Lockup Syndrome. I have had both shots and still hiding from something or someone. I'm just following the voices in my head.
You can add capacitors for added accuracy/stability to the VR input and output pins. Not needed for our gas gauges. You can mount them on a pc board or rig them separate. You can add heat sinks, not necessary for the amp draw/wattage of our gas gauges. As I said before, these linear voltage regulators take a very unsteady higher input voltage and supply a very steady output voltage. These devices have built in thermal overload protection and short circuit current limiting. They are identified by letters (L , LM, etc. depending on manufacturer. National Semiconductor, Fairchild Electronics, etc.), then 78 and then the output voltage. KA7808 has a 8V output. All kinds of output voltages are available. XX7806 is 6V output.
A person wishing to build their own "Runtz" or VR can use any method they wish. As stated, wire them direct from battery. If I tried it, I would just solder wires directly to the three TO-220 pins and cover with heat shrink sleeving as the Hamb link shows. No heat sink. If I ever needed a reducer for a gas gauge, I would buy one from Classic Trucks for $6. Wire it direct from battery (just in case) and use an inline fuse to protect gauge. If the Runtz is wired direct, meaning no spikes, why is thermal overload protection and short circuit protection such a big sales feature? (Rhetorical)
Remember when getting all technical about this, that our gas gauge are inaccurate due to temperature variations. The gauge itself is a slow reacting, slosh dampening, needle to hash mark mismatched design to begin with. I'm like Carl, I don't look at it much or worry if it's not aircraft accurate. You will learn where empty is soon enough. Just get about 6V to it and be done. Lots of guys run them on 12V. Voltage drop keeps them going. So just run 14 feet of wire to them.
