Wiring a Smiths tach

argatoga

argatoga

Can't Start His Wank
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Oct 4, 2005
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Location
Zagreb
Car(s)
'08 Pontiac Solstice GXP
My MG has an unconnected Smiths tach (well the light is connected). I'd like to wire it up and see if it will works. What needs to be hooked up to the tach for it to work? According to http://www.geocities.com/mg12a/mg12a/intro.html I need to do the following:
Power goes to the coil (+) and to the ignitors (2) ( located on the distributer. These wires are heavy gauge, and black with white striped tracers. The yellow/green wire from the ignitors go to the corresponding coil ( leading or trailing) (-) side. To get the tach to work, the tach must be connected in series with one of the yellow/green wires. Disconnect the black/white wires going to the tach. These wires have bullet connector ends, one connects to the ignition switch. Cut the y/g wire, and connect the ends to the 2 bullet connectors on the tach. They can be hooked up backwards, so if it doesn't work, just swap em.
Click to expand...

So am I to split the y/g wire and have the tach connected in-between the coil and ignitor?

Also if it doesn't work can someone recommend a good replacement which will fit the look of the other dials.
 
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Do you have a photograph of the Smiths tach in question? Jaguars used a (possibly similar) Smiths tach into the early 80s when Smiths bailed out of the automotive market. If I can see it, I might be able to advise you if it is correct (as BL and Leyland Leftover cars often shared more than a few parts.)


Smiths instruments are back in production thanks to a successor company of Smiths, called Caerbont Automotive Industries. So you can get "new" gauges now.

Edit: It looks like your assumption is correct - plan B would be to connect a new wire from the (-) negative side of the coil to the tach, and then run another one from the tach to ground.
 
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Anywhere on the chassis or body should do. You could even "reuse" bolts in the firewall, floor, whatever. Just check them with the multimeter before assuming they're a good ground.

And you don't have to be able to solder to make this work. Go to a NAPA and get some Crimp And Seal connectors of the appropriate type and size for the particular wire gauge. Crimp them on, then use the built-on heatshrink tube to seal it.

Almost no factories use soldering to make such connectors. They all crimp them, so don't be afraid of crimping! Get some good crimping and stripping tools then have at it.
 
Ah good, crimping will make things easier if I go that route. I didn't think of using an existing bolt (too late for my brain to function).

I only see one bullet connector on the tach above. Is there a female one hidden on there? Unfortunately my tach has become one with the dash and won't remove itself easily, forcing me to look up at it from a bad angle.
 
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No idea - but there should be. Someone may have swapped out the tach for another one - Smiths tachs are notoriously interchangable; some Smiths tachs are one-wire and rely on some other method for grounding.
 
Well I gave it a look at before dropping it off at the mechanic the other day and it looks like I do have two bullets. When I get it back I'll see about wiring it in.
 
I got around to trying this. I hooked up a new cable from the tach to one of the negative coil connections and another cable to a ground (an unused screw in the engine bay). No dice. I swapped the two and it didn't seem to work. The only cables running on the back of the tach are the ones listed above.

Is there an easy way to test the tach? And what would be a good replacement?
 
Check into the Spridget forums and make sure it's hooked up properly.

You could replace it with an Autometer gauge, and in fact that's a good way to test it - hook up another tach like the Smiths is hooked up and see if it works.
 
I have a cheap sunpro tach in my Jeep from autozone and it has worked perfectly for years, even in the dust/rain.
 
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