If your speedo needle has the shakes, you need the Stabilizer unit.
The fuel gauge mounts inside the speedometer just above the center of the mph dial.
It sometimes happens that the speedometer works fine but the odomoter does not. The units occupy the same housing and the fact that the odometer does not work is not any indication of trouble with the speedometer itself. There are instructions on line for disassembling the speedometer and tinkering and fixing the odometer gears within. The work is pretty tricky and involves tinkering with the gears. There are speedometer specialists out there that do this professionally and can receive, repair and return your speedomter with all repairs done. You can do a search on "Beetle Speedometer Repair" and a couple of videos will come up and also ads for specialists who work on VW Beetle speedometers. Here is one that is clear and thorough by a guy who did his speedometer overhaul and posted thorough directions (note: speedometer dismantling and repair is not for the faint hearted !!) so copy this url and paste it to your browser: http://dragonflypower.com/VWspeedometerHow2.htm