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Factory tach and center gauges without changing harness?
The tach itself wouldn't that big of a deal, except that it's constructed with Ford proprietary wiring - which is why they guys are steering you the direction they are.  If it were an aftermarket tach, it wouldn't be tough at all to simply run your own lines and following the manufacturer's instructions for installation, as you're thinking... but Ford engineered these things to work off specific voltages and resistance, so your results might turn out a lot differently than you're hoping for.

As for the center gauge cluster, I'd probably just replace the gauges with aftermarket units and follow their directions.  You'll have 'almost' the factory look, but won't have to mess with the factory harness.  Member jpaz has a thread going right now about swapping in some aftermarket gauges that look pretty awesome.  https://www.7173mustangs.com/thread-cent...ges--33369

There are also some other threads floating around where others have done the same with excellent results.

I'm with the guys on this - digging into the factory harness looking for something that's not there isn't the best way forward, IMHO.  Tach and 3-gauge cluster cars came wired with those circuits from the factory.  I also bought a tach cluster and harness from a friend on another site a long time ago, thinking I could just swap things and it turned out to be very much NOT what my car needed (tach cluster, sure... but not so much the 3-gauge cluster, and the fact that it was from a '73 where mine's a '71).  So I gave up on that idea and went with an RCCI clock/tach conversion and haven't looked back since.

Not saying you can't do this, or trying to discourage you in the least.  Just echoing the other guys in saying there's an easier, possibly safer, way to do what you're wanting.

Hope this helps!


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One of your questions was about the actual plug going into the cluster. Yes it is different between gauges and idiot lights. Gauges have a smaller / shorter plug. One of my cars had the harness all hacked up and yes I did change the whole thing from headlights, engine and under dash.
It is difficult to find the exact harness you need. Each harness is different depending on what options your car has, Air, vert, gauges, tach, etc. 71 & 72 is also different in a few places than 73. I hate wiring.
If you do change out the harness it is easier to pull the whole dash out.  If you do that then go ahead and replace your heater core, lol. One of those snow ball deals.
Couple pics of back side of dash and the hacked up harness PO had done that I removed. Note the spliced wires going to the plug for speedo.
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When a man is in the woods and talks and no women are there is he still wrong??
(12-28-2018, 12:37 PM)TheDude Wrote: Sorry, I must be thick headed, but I'm not really getting what the issues are with just running wire from the coil and sensors under the hood to the back of the tach and other gauges.

I actually do have a complete wiring harness as well from the donor car, I just am having a hard time understanding why I would need to use it other than to make things look factory. What's the issue with just bringing up those cables from the engine compartment to the dash?

Is the connector on the back for the speedo / tach pod substantially different? Obviously it would have the extra wires in it for the idiot lights and none for the tach. Is the actual plug different though?


It's not really an issue, more that the guys are trying to steer you to a more robust and reliable setup. 

I have done the non-gages to gages conversion with the harness in place and it's kind of a PITA. You'd need to source the correct tach cluster connector, as well as the dash harness side connector for the center gauges. You then need to swap the connectors on the speedo cluster, easiest way is to remove the pins one at a time and move them to the correct locations on the new connector. The wires for the center gauges will be left and you'd need connect them to the connector. Regardless, the ammeter will never work unless you rewire as midlife noted previously. At that point, it would be smarter to have Rocketman do the voltmeter conversion on that, as it's more accurate anyway. 


For the tach, you need to dig into the harness and connect it inline before the ignition power wire mates tot he engine compartment harness at the fuse box.

To be honest, if I were to do it again, I'd leave the idiot light harness intact, get a Rocketman tach conversion on the warning light face and also run aftermarket gauges that fit in the factory center pod. Idiot lights are more in your face when something happens, than a gauge that's totally out of your field of view. 


Here is an article that may or may not help. As for the ammeter you may want to put a voltmeter in there instead. 


Here is rocketmans converted ammeter:

(12-29-2018, 04:42 PM)SteveO_71 Wrote: Dude,
Here is an article that may or may not help. As for the ammeter you may want to put a voltmeter in there instead. 


Here is rocketmans converted ammeter:


Thanks! That is exactly what I was looking for.
Oh jeez, Pazjer's hack-n-whack conversion how to lives on....

[+] 1 user Likes Hemikiller's post
(01-07-2019, 09:07 PM)Hemikiller Wrote: Oh jeez, Pazjer's hack-n-whack conversion how to lives on....


Let me check your shorts!

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