2-wire speed sender electrical test
The testing is the same for all 2 wire senders, screw-on or OE integrated style.
1. Using a multimeter set on AC voltage
2. Probe one side of the sender wire with the red lead, the ground wire with the black lead. (senders that have been removed from the vehicle (screw on) wires are interchangeable
Spin the sender shaft with a drill (screw-on style) or spin the tires. You should see voltage on the signal wire. Most speed senders will output between 8-18V AC. NVU speedometers will read down to 4V on most occasions even though the specification for aftermarket products is 6V.
You will see the voltage climb as speed increases. You can also see this VIDEO for screw on-types
YES I SEE VOLTAGE ABOVE 6V-speed sender is good. IF SPEEDOMETER DOES NOT OPERATE CHECK CALIBRATION AND SIGNAL AT PLUG/SPEEDOMETER CONNECTION.
YES I SEE VOLTAGE BUT IS IS BETWEEN 3-6 V
I DO NOT SEE ANY VOLTAGE OR IT IS VERY LOW
Speed sender is most likely bad or going bad. You can as a last resort beofre contacting the speed sender manufacturerfor the output signal strength specifications. You may also want to try changing the speedometer input sensitivity on air core speedometers.