70 Mach1 tach conversion question

[miketyler 15]

I had Midlife convert my under dash harness over to tach cluster. I need to buy alternator wiring harness for the car and notice the alternator harness is different for tach cars. From the pics, it looks like it has three terminals on the alt instead of two. Is the alternator different between tach and non-tach cars or?

 

Edited June 21, 2011 by miketyler

[TexasEd 190]

Here is a good reference site with pictures of the various instrument clusters for 69 & 70.

http://1970mgr.org/_DifferencesGauges.htm

Tachometer equipped interiors were arranged from left to right: Temp, Speedometer with Trip Odometer, Tachometer, Fuel. The ammeter and oil pressure gauge is deleted and an oil pressure warning light and charge indicator light moves to the lower tachometer face.

 

So in a factory tachometer equipped car there was no ammeter, just a warning light on the tach.

[miketyler 15]

Yes, I get that. My question now is what else must change as a result of the conversion.

 

Here is the alt harness for cars without tach. So I should purchase this one? I would have to look at back of my alternator to see if there are three posts on it to accomodate the harness made for tach cars. It looks like to me that tach cars may have had a different alternator?

 

Edited June 21, 2011 by miketyler

[TexasEd 190]

Sorry, you are looking for which harness goes on the alternator.

 

Are you using the original alternator or a newer model, I know that makes a difference and a newer alternator can burn out an old gauge.

 

I would check with midlife on what you need if you can't figure it out.

Edited June 21, 2011 by TexasEd

[miketyler 15]

I have a PM sent to him, figured someone here had been there and done that.

[stangs-R-me 120]

Both use the same alternators ... the extra terminal is just used with the one and not the other.

 

Yes, you need to get the Tach specific front harness as well as the Tach specific alternator harness.

 

OR, you can do as I did and swap in a non-tach cluster alternator gauge in place of the Tach cluster temp gauge and add the Shelby styled pod in place of the ash tray with aftermarket oil psi & temp gauges. Requires some minor wiring, but you keep the non-tach front harness & alternator harness PLUS you end up with REAL temp & oil PSI gauges !!

 

See attached circuit drawing PDF ... it ends up being very similar to Cougar XR7 (which has full instrumentation and uses the Mustang non-tach front harness & alternator harness).

 

Doug

[miketyler 15]

Assume you are talking about headlight harness? I have a new one already but don't see any designation for a headlight harness with or without tach? I see them as with or without sportlamps. The tach alternator harness connects the same way as the non tach but does pickup one more terminal on the alternator. Maybe there are leads that are present but otherwise arent used on the non tach version

[Powershift 19]

You can also do a standard 3 wire tach conversion. My buddy, Miles Cook, did it to his '69....

 

http://business.highbeam.com/435580/article-1G1-140145713/install-6970-tachometer-gauge-cluster-redline-gauge

 

"Thanks to Mustang Country, here's what we know: Redline's three-wire tach conversion means it's no longer necessary to replace a car's entire underdash, non-tach wiring harness with a tach version. A car's existing non-tach harness can be altered to work with a tach cluster, since the tachometer itself is wired separately and is no longer connected through a factory Ford harness. Wire cutting is also not required: The existing harness's main plug is simply repinned according to a factory Ford wiring schematic that's available from most Mustang parts houses. In addition to the speedometer (with its cable) and tach working on their own, relocating the wires in the cluster's main connector means all the secondary items in the cluster will work properly, including the high-beam indicator, the turn signals, the fuel gauge, and the in-dash lights for nighttime illumination."

[stangs-R-me 120]

Assume you are talking about headlight harness? I have a new one already but don't see any designation for a headlight harness with or without tach? I see them as with or without sportlamps. The tach alternator harness connects the same way as the non tach but does pickup one more terminal on the alternator. Maybe there are leads that are present but otherwise arent used on the non tach version

 

1969 front (headlamp) harnesses are different between Tach & non-tach cars and the fact that 1970 & 1969 headlamp harnesses are NOT the same slipped my mind yesterday.

 

The hood scoop T/S wiring was separate in '69 where it was incorporated into the Mach 1 (Sportlamp) harness in '70.

 

So maybe they incorporated all the wiring for both Tach & non-tach in the two '70 headlamp harnesses to avoid having FOUR different harnesses.

 

Doug

[69gmachine 15]

Assuming you're installing the complete tach cluster, I would recommend making the alternator light functional by adding the wire however you do it to the alternator. The factory 69/70 altimeters always burn out shortly and are completely useless after a year or so of use (notice the needle never moves off center?). The light however will tell you the alternator is NOT charging, and you can bank on it. If that light is on, you are not charging the battery.

[miketyler 15]

I think Midlife adds that wire as part of the conversion. Ideally would be good if it came on with key on but I suppose oil light already does that and helps to make you visually aware that the key is on?

 

There is also a good article here on the repinning of the plug for tach conversion.

 

http://www.boss302.com/tach.htm

Edited June 22, 2011 by miketyler