Trip Computer XJ-S

Does anyone know what the amplitude (voltage) of the square wave signal from the fuel and speed interface modules to the trip computer are on a ‘88
XJ-S? This would be what the trip computer is seeing on the orange and yellow wires.
I know the speed signal is 800 pulses per mile, and fuel is 8000 per gallon US. I have read 10v and 4v…
My trip computer records gallons used quite accurately, but mileage registers only occasionally. Speedo and cruise both work fine, so I am assuming that the differential mounted sensor and the speed interface module are ok.