I asked about this sometime last year, but cannot find it in the archives: I need to hook up my electronic speedometer on my Jeepster but cannot remember how to hook it up: it seems pretty simple if I’m not mistaken. Does anybody remember that.?
Is it the Jag/Smiths type of transducer that looks like an angle drive but with wires instead of a cable? Is the Speedo a Jag matching period instrument? Both should have a short pig tail/multiplug IIRC If so do the wire colours match? If they are both Jag items the diagram will be in the Haynes book and is probably like the early S2 tach with just a dedicated pair of wires running between the two.
Subject to answers on the above I’ll look it up.
Thank you Peter: I don’t have the Haynes manual nor am I going to get it. It’s the newer S3-style transducer with two wires out, two wires go into the speedo and just not sure how to hook them up in terms of power.
No, didn’t expect you to look 'em up, just confirm their origins. Both should have green and yellow wires.
Green is ign switched power +ve
Yellow is the sensor/sender link.
Speedo probably has a black wire -ve earth.
Thank you. Plus 20 speedos.
Did it work??? 20
The wires on the transducer do not match those on the speedo: transducer has a yellow/black, and a brown. Speedo is yellow and green (I have none of the intervening wire harness).
Just don’t want to hook up the +ve to the wrong side, and fry something.
Brown is power unfused, green is power, yellow is signal.
I only see two wires out of the transducer, and two wires out of the speedo…?
Tha diagram doesn’t label speedo ground color, or even definitively say its a wire - hence my conditional mention of a black wire st speedo head. It is probably a panel/casing earth. The transducer diagram doesn’t even show that, so either there’s no sensor earth or it too has negative through the sensor body to power unit castings? An electronics oerson will know the needs but positive feed and negative earth can’t hurt (I assume - hahaha).
I believe the transducer is just a switch that gets constant 12v and chops it up. No ground required. The yellow wire goes to the instrument and as soon as the Instrument gets ignition power it translates the pulses into needle position. Ground should be through the case; the dashboard is grounded, the wood has a steel backing.
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Ok… but what is the second wire for, on the transducer?
Power in, signal out?
Maaaybe… just wanna make sure, if true, to not hook it up back asswards!
I‘m only careful with my go ahead because the tach I wired up on the little test stand hasn’t worked so far. …I think I just figured that one out, no ground, brilliant 
I have a tach somewhere, if I can figure out a transducer I can tell you positively if you’re that worried.
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FWIW, this is the speedo.
**
The transducer green wire is 12V and co-connected with the green wire at the speedo, powering both. Diagrams do not show where the junction is. The yellow wire goes from transducer to speedo - and eventual lack of markings on the transducer may indicate that wires can be connected either way?
Speedo ground should be speedo body, as David says. It’s weird that ‘+’ and the transducer connectors are clearly marked - being electronic ohming between either and speedo body will both show high(?) resistance. But if different; the resistances offer no explanation as to which is which…?
Frank
xj6 85 Sov Europe (UK/NZ)
^^
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*…I have a speedo here (mph even) and figured out why my tach (v12 rpm) doesn’t work. Oops
Anyways, green and brown are power wires and yellow is signal so I imagine that should work.
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No joy: I really need to find a way to understand the basic theory of operation of this system.
I hate flying blind.
Does this help?
The theory, in essence, is that the transducer takes 12v+ and turns it into some sort of signal (wave form?) that the speedometer can use.
Transducer failures are common. Maybe you have a dud?
I think you can use a voltmeter to determine if the transducer is creating a signal. That is, at least tell you if it is …or isn’t …outright dead.
Cheers
DD