I will edit this post because it was a lot to unpack and there is more to add, but for now, I will post the resistance numbers for the currrently available VDO gauges. You need these numbers to have a speedo shop modify a Porsche OEM combo gauge to work with our fuel and temp senders. Palo Alto Speedo read through this data, and it was what they needed to set my gauges for a VW fuel sender and VW temp sender.
Fuel sender
For a VW bug/Current VDO:
Empty- about 73 Ohm
Full- about 10 Ohm
The stock tank unit is about 10 ohms full 73 ohms empty.
For a Porsche 356 OEM gauge: Empty should be 6 ohms, full 200.
Oil Temp
For a VW/Current VDO, I found a topic where it said that the resistance needed to be high when it was cold, and the resistance low when it was hot. This is exactly what the poster did. It read 1240 ohms cold, and 210 ohms hot.
For a 356 OEM Oil Temp Gauge: 28 ohms at normal room temperature, about 74 F
the resistance increases with temp rise and at 180*F measure around 40 ohms
VW Oil pressure: The sender has a 100 ohm resistance and the gauge should read 40 psi. 150 ohms will make it read 60 psi. However, the idiot light is either on or off. There is no conversion, as a result. It is just a matter of plugging the idiot light wire into the 356 OEM idiot light bulb socket/spade.
From the VDO website
Fuel Sender 221-012 (VW tank), VDO Lever arm fuel sender 12/24V for Classic VW beetle 73-10 Ohm
Oil Pressure Switch 230-504
Temperature Sender 323-417 300-1000 ohm
