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Speedo transducer testing
Donners90 - 19/10/04 at 11:35 AM

I have a speedo transducer from an LT77 gearbox and I'm trying to establish whether it works or not. Can someone tell me how to do this with it out of the box (on a bench)?

Cheers

James

loafersmate - 19/10/04 at 11:56 AM

If it has 3 wires (hall effect) then you will need to connect 12v (maybe 5v, check wiring diag in haynes)to one of them, ground to the other and there will be a pulse generated on the 3rd when you move a piece of magnetic metal past the end. If it only has 2 wires then one is ground and the other the signal. You may get a small bulb to flicker with a 3 wire type or a multimeter for 2 wire.

Cheers

Ben

Donners90 - 19/10/04 at 09:10 PM

Thanks Ben.
It has two wires, one brown and one yellow/black. Is it possible that the brown is +ve feed, the yellow/black wire is the signal, and the body is -ve? I ask as I have discovered that other (Ford) testing procedures require 3 wires for similar transducers. These testing procedure say to use an oscilloscope to measure a square wave, but I was trying to find a 'homemade' way of doing it.
Cheers
James

loafersmate - 20/10/04 at 07:24 AM

The output from a 2 wire will be an AC pulse which you 'should' be able to see on a multimeter. One of the wires should be ground and the other is the signal generated by the magnetic trickery in the sensor. Whip a piece of metal past the sensor end and see what you get! (maybe mount something in a drill and hold the sensor near with the signal line connected to your tacho)

Cheers...........Ben

wilkingj - 10/3/06 at 07:43 PM

Just in case anyone else is trying to find out...

I have just got mine working, but not calibrated yet.
Greengauges Speedo and LT77 Sensor.
Yellow wire to +12V Brown Wire to the speedo, and had to ground the red wire on the speedo Greengauges say to do this for Quenched oscillator type.

I have got a clue what the sensor is. But it is for a LT77 Box.

Also there are different ratios for the sensors: (Same Speedo head on the SD1's??)
sd1 notes are;
1-black 20 teeth 3.08/1 [final drive]
2-orange 23 teeth 3.45/1
3-red 22 teeth 3.9/1
Although I am using a Ford 3.62 Diff, so will need to work out a new ratio on my speedo head (switch settings).