Speedometer not working

[ksamson]

Hello Roadsters, I have a Ron Francis Roadster harnes. I have a 200MPH Autometer Speed gauge. I have a electric 2-wire sending unit. I believe I have everything connected correctly. I was a little fuzzy with the 2nd gray wire that goes to the ground.

1. Green Wire to Sending Unit
2. Gray Wire to Sending Unit

3. 2nd Gray Wire to a ground?

Any help would be appreciated.

[Retirement Toy]

Yes, the gray wire goes to ground. the instructions are not clear, but that worked for me. Remember you have to calibrate the speedo, instructions should be in the box the speedo was in.

[ksamson]

Thank you, correct me if I am wrong but it should still spin while driving it even without calibration? Correct?

[Walt]

My harness only has one grey wire that is with the green at the speedo, I grounded it to the frame and worked fine , also I have the 160 mph autometer set.

[ksamson]

ok so do you have a 2-wire sending unit?

[Walt]

Yes the green and the grey both come from the sending unit on the tranny, this is a stock T5 and ford speed sensor.

[skullandbones]

Thank you, correct me if I am wrong but it should still spin while driving it even without calibration? Correct?

Don't know about the 200 mph model but I would think it would have a similar calibration procedure to the 160 version. They don't move until you calibrate them. You can start the calibration steps to see if you are getting power though. I remember calibrating mine right after I went to register my car since I didn't have a secure place with a 2 miles stretch to do it while I was illegal. It is a good feeling to see it work!

Good luck,

WEK.

[edwardb]

Don't know about the 200 mph model but I would think it would have a similar calibration procedure to the 160 version. They don't move until you calibrate them. You can start the calibration steps to see if you are getting power though. I remember calibrating mine right after I went to register my car since I didn't have a secure place with a 2 miles stretch to do it while I was illegal. It is a good feeling to see it work! Good luck, WEK.

This may not apply to your situation, but the Speedhut speedometer in my Mk4 build worked immediately once it was wired up. The needle was deflecting at first start when I spun the back wheels, and I was getting an indication when I did the go-kart a few weeks ago. I haven't started any calibration steps yet. I suspect it's not accurate (may not even be close) but this brand at least moves the needle without calibration.

[stevem]

I have the autometer speedo from FFR. Worked after grounding the gray wire but was way off until calibration.

[Doutie]

Hi guys, I'm a truck mechanic and large trucks use the same technology and I thought some basic explaination might be helpful. In the tranny is a special gear, whose teeth pass by the sensor and create the signal the speedo reads. As a tooth approaches the sensor it creates a positive voltage, at the center of the sensor 0 voltage and as it leaves it causes a negative voltage. Between your green and gray wires coming out of the sensor is a (AC, alternating current) voltage. The speedo head counts the number of teeth going by the sensor to determine how fast you are going. The calibration process tells the speedo how many pulses per mile your arrangement needs to read correctly. When diagnosing a nonworking speedo I will jack up the vehicle, set my volt/ohm meter to read AC voltage, connect the meter to the two signal wires at the back of the speedo and run the rig. As I increase the speed the AC voltage increases, maybe three volts at highway speed.
If I have no voltage then bad wiring to the sensor or bad sensor. If I have a voltage signal then I have a problem with the speedo itself. Most of the speedometers
require a keyed voltage source and a ground so those must be checked before tossing the speedo.