IC is short for integrated circuit. If you want to know what is inside that black plastic cover you can look up the circuit by the part number. But that won't help much unless you have some education in circuit theory. But for just us few that want to know...the inside is a solid bit of material with some chemistry differences at very specific locations that change how the material reacts to current. They grow this stuff. No parts in there at all. Now that we all are clear on what is in there...:). There is an "op-amp" and some bias resisters that make it work. OP-Amp? Short for Operational Amplifier. The difference in the one part number to the other one posted by Denny Graham is the material and it's ability to conduct current. Higher rating means more current. lower rating means less. So, for the fuel gauge you don't need much. For the heater? Well that will take a lot more. And a radio? 6 volt has a "vibrator" and tubes to heat. That will take as much as heater. "Vibrator"? That is how to make radio frequency A.C. from D.C. voltage.
Weeds: Black is ground. One Red is 12 volt in. And the other is 6 volt out. Should be clearly marked.
Are we having fun yet?
Enjoy.
