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Hi all,
I'm wiring up my tach today. as near as I can tell, one wire would have gone to the + terminal on the coil and the other to a 12 v switched source (near as I can tell). So which went where is my question. There is a red wire and a deep purple (or black, I'm pretty colorblind) coming out of the back of the tach. Which is the trigger wire and which is the ignition switched wire?
 

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tach wiring

Any tach that I have wired I had one connection to
each side of the coil. I have never hooked one up
that came standard on the vehicle however, like your xr7.
 

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The tach connections plug into your existing wiring. There should be a red wire coming from the ignition switch connector, then it plugs into a pink wire that leads to the firewall disconnect. Unplug those two wires and plug the tach in between. The pink wire is a resistance wire and is a carbon core so handle it with care.
 

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My tach doesn't always work...anyone know why?
 

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Royce, please excuse my ignorance here.

I'm installing the MSD 8920 Tach adapter like Kirk was. I found the pink resistance wire you described, as well as two other red ones. One is red with a yellow stripe supposedly feeding the brake warning light and the other is red with a green stripe coming from the ignition switch. I'm a little puzzled by what you mean by "connecting the tach in between those two wires.", the pink and the red ignition wire?

My entire ignition system is MSD and it was previously running to an Autometer Tach. My stock tach was completely disconnected. I now want to implement the stock one again and need to know which is considered the "trigger" wire for the tach. I know with the stock ignition, it passed through the tach in order for the car to run. I've already reconfigured that years ago when the stock tach was disconnected.

I think all I need is just a little more clarification and I would be forever indebted to you. Thank you.

Mark
 

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Mark,
Kirk is installing an XR-7 tach in a standard Cougar. I am describing the stock hookup in my previous post to reply to his question.

To run the stock XR-7 tach with an MSD use MSD's instruction sheet and wire it accordingly with the tach adapter. I run that setup in one of my cars with an MSD6AL and Pertronix converted stock distributor. Works great.
 

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I understand what you mean about Kirk's question. Like I said, I'm ignorant with this one. Which wire did you tap into as the trigger wire? Was it the one from the ignition switch, the resistance wire, or the one that goes out to the brake light warning light. Thanks again for not blowing me off.

Mark
 

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Mark,

There are two wires coming from the tach. You use the trigger from the MSD unit. None of the wires originally hooked to the tach are used.

I used the schematic from the MSD tach adapter. It was straightforward as can be. Don't remember exactly what I did other than follow the directions. Took all of five minutes to hook up. This was ten years ago and the details are fuzzy. I hid all the MSD stuff inside the console behind the clock so it's not easy to see either.

If you can post the schematic I can tell you the answer to your question.
 

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Discussion Starter #9
well.....

Well, I got it hooked up and it worked great, but then I took the clester out to do some more work on it, my 15 month old son proceded to remove the needles from the tach and speedo. They weren't in the greatest shape and the backing had already been butchered by a p.o. (That's why I got it cos I didn't want to hack up a hood one). Anyway, I decided to ditch it and do a custom cluster with autometer gauges. Only problem was the new tach and speedo are 3 3/8 inches and the holes are 4 inches, which was an excuse to go with a brushed alluminum dash piece and I figured I should do a matching piece for the top of the console. Will take some pix of how it turned out. I think it'd be easier to go with a 5 inch tach and speedo, but I had to skimp somewhere as this was an unplanned expenditure. Maybe somewhere down the road.
 
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