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Found these gauges today


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The car I salvaged these from is a '77, which had the Lucas fuel injection, and I don't think I'm going to go and switch out all my wiring to run a V12 with that setup. In fact, just to rebuild these engines is expensive as it is. I just want to use the gauges with my car, which I think is possible. The place I work at deals with Subarus and Jags, so there might be a technical manual there that might have the schematics on an old smiths tach, but alot of their older books hidden in locked cabinets. Also, if what I think is a resistor is, in fact, a capacitor, what's with the stripes? I've never seen a striped cap before in my life - Not even in older stuff.

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I suppose you're right. I guess that a couple of alternatives would be to either A: Use the circuit board from a 280 tach, or B: Just find a way to adapt the face of the Smiths unit onto the 280 tach. Also, I just found an XJ6 tach at the junkyard today (who'da thought another one would show up!), but the stupid thing only goes up to 5000 Rpm before it redlines, so I'm not sure I could get that to work on my engine, unless I somehow solder that 6 board onto the 12 tach. Guess I'll have to take another picture - this time, of the 6's board...

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  • 1 month later...

So today, I decided to do a little experimentation, and de-soldered that striped component (which I'm positive is a resistor of some sort) and soldered in a 10K potentiometer. I then, pulled out my stock tach, and hooked up the wires to the Smiths unit, fired up the car, and notice that it works. However, it only runs up to about 3500 RPM then dies off a bit. I have the red wire with the female bullet connector on the bullet male of the tach, the green wire on the spade, and the black wire on the ground of the tach body. I know I'm close to getting this to work properly, but I still think I'm missing something here. I pulled open the stock Z tach, and noticed that the ground wire also goes into the tach circuit. I wonder if I need to use that black wire on the same terminal as the green one? Since it might just be a second signal wire, but I'm not 100% sure.

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  • 2 weeks later...

Okay, so the 'resistor' replacement trick didn't quite work, but I came up with a proper solution. I had a tach from an XJ6 sitting around, so I used the circuit board from that, and soldered it to the XJ12 unit. Hooked it up today, and it works perfectly. Also, the two big guages are installed in the car now with brackets welded to the cans made from the stock gauge cans. All I need now is a proper fitting speedo cable, which I'm sure I can have made at a shop or something. I'll post pics of the gauges installed with new LED backlighing working next time.

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