Mark

Please reference rotate.aero/forum/test-equipment/224-fuel-quantity-test for fuel quantity basics and test box usage.
Please reference rotate.aero/forum/767-28fuel/765-surge-tank-sensors for one example of using the test box.

There is a cable connection issue when it comes to using different manufacturer Fuel Quantity Test Units.

Some, have reverse polarity BNC connectors.
  
     
  
On this Viavi  box, the LoZ and Comp connectors are males. The HiZ is female.

Most co-ax test cables are male on both ends, which connect to the HiZ BNC connector.

You must have a set of special cables made up (male on one end and female on the other.....
  
     
  
.....or what I call "gender-bender" adapters to use for the LoZ and Comp BNC's.
  
     
  
These are somewhat hard to find. I ordered some from a place called Show Me Cables .