Wow! Looks just like any other 81-83; 'cept it's a '79!
DISCLAIMER:
Usual stuff. This is taken from my own experience, and it assumes some knowledge and ability with auto repair, particular electrical wiring in this case. If you get hurt, it's not my fault. You've been warned! Actually, there shouldn't be any problems here, but if you burn down the car, don't come crying to me; I'm assuming some common sense here. And, of course, your mileage may vary!
WHY WOULD I WANT TO DO THIS?
I did it for the oil pressure guage included in the later guages, and the voltmeter that works all the time, not just when there's a problem. I also prefer the amber text and illumination to the white/green of the earlier guages. The only drawback is that you lose the clock. My radio has a digital clock built in, so no prob there.
OK, WHAT DO I NEED?
First, of course, you're going to need the aforementioned guage pod. As far as connections, they're all the same, but some have federally mandated 85 MPH speedos (now wasn't THAT a ridiculous idea?). These are actually more accurate at low speeds due to the greater relative sweep of the pointer, but i prefer the 130 MPH speedo for testosterone induced reasons. :) Along with the pod, you'll want to get the connectors and about 6-8 inches of the wiring harness. You may also want to get the AC control lens so that its text matches that of the guages. Find a really twisted up wrecked Rex to do this, so you don't deprive someone of an otherwise rebuildable RX-7, OK? 'Course, if it's in a wrecking yard anyway, it'll eventually be crushed. Oh well. Grab as many parts as you can! It's giving its life to save yours, make it count!
GOT THE STUFF, NOW WHAT?
From here, there are two ways to go: you can cut the connectors off of your 79-80 and simply solder the 81-83 connectors on, or you can do like I did and fabricate an adapter harness. I've done this on most of the mods I've made to mine so that they are reversible, should I ever get the resto bug and want/need to return to factory original.
Check out the two diagrams below. the first is the pinouts of the two pairs of connectors, the second is the pinout for the adapter plug that will need to be fabricated should you go that route. On the first diagram, you'll note that there are more pins on the 81-83 than on the 79-80. Fear not, these are mostly idiot lights that you don't have sensors for. Incidentally, these diagrams are based on info from the wiring charts in the Haynes manual for first generation RX-7s - they're not always complete, but very useful for stuff like this. Also note that most of the colors for the same purpose match. This helps somewhat for those of you cutting and replacing the connectors. Basically, just match up the same connection on each connector.
For those of you not wanting to cut your original wiring, we'll have to make a male plug to attach to the cut end of the 81-83 harness, and plug into the 79-80 connectors. The second diagram gives the layout of the plug. I cut disks of appropriate size (measure your connector) out of 1/16" plastic. I used sheet Styrene from a local model shop, but almost anything the right thickness and nonconductive will work. The right thickness is determined by the pins used. I used .093" Molex pins from radio shack (The didn't sell the pins separately, so I had to buy the whole connector - check other electronics stores). You'll need 18 pins, total.
I have since created an accurate template for the disks on AutoCAD. I have a GIF version of it that you can download and print out. Just resize it until the 1-inch dimensioned line at the bottom actually measures 1 inch. I have also posted the AutoCAD DXF file that the GIF was generated from.
Now you can drill out those holes with, I believe, a 3/32" drill (test first). You'll also have to drill a hole in the center to clear the indexing pin on the 79-80 connectors. Now cut out the disk. If you want to be ultra-neat, you could use a hole saw, but heavy shears will work fine. A perfect edge here isn't necessary for correct function. In fact, you could simply stick the pins into the connector, but this is neater, and easy to reconnect should it come loose.
OK, time to wire it all up! The second drawing shows the wires you're going to need. I made my adapter about six inches long - there's plenty of space behing the guages. Get everybody cut to length, then strip about 1/8" insulation from the end of the wires indicated in the diagram. Crimp Molex pins onto each of the wires (there is actually a special crimper for Molex pins, though I used standard crimpers at the time); it may be a good idea to solder the conections if you know how. Now insert the pins through the holes until they click in - remember that the diagram shows the side of the connector that the wires will stick out of; the pins will stick through to the other (back) side. It may be necessary to hot glue 'em all in - go right ahead, but make sure it'll plug into the factory connector first! In fact, plug it in, then hot glue it while it's plugged in - the pin orintation will be near perfect. There is one additional wire you'll need - the brown w/ yellow stripe wire will need to be extended out to the engine compartment, and an oil pressure sender installed and connected to it (don't ask me how - somebody put an 81 motor in mine before I bought it!). Tape everything up to prevent any shorts, plug your adapter into the 79-80 connector, then plug in and install the guage pod. The 81-83 pod fits and secures exactly the same way as the 79-80. Don't forget the speedo cable!
Turn the key to "on", all the guages should begin reading (tach should zero), and most of the idiot lights should come on. Check lights, high beam indicator, signal indicators, and the idiot lights you can trigger yourself (brake, rear defrost, HL motor). fire it up, make sure tach and guages work, and you're done!
