Putting an 81-85 electronic distributor in your '79 RX-7

Back to Modifications Page

DISCLAIMER:

Working on cars can be dangerous. Heck, *life* can be dangerous. Be careful and observe proper safety and you should have no problem. We're also working on the ignition here, so there is a potential for zapping things, including yourself. If you don't feel comfortable with that, get someone who is to help you.

AND I WANT TO DO THIS BECAUSE...?

Well, have you had to adjust the gap on the points yet? Both pair? GM had a nify solution to this problem by including an access panel in the distributor cap that allowed you to set the dwell (a more accurate measurement than gap) while the engine was running. No such goodness from Mazda. It's either set them with feeler guages, or set them, put it all back together, check dwell, take it apart, re-adjust, lather, rinse, repeat...

Updating to the later-style solid state electronic distributor means no more points, and, as a bonus, you get to actually power the coils at a full 12V +! You see, those big, ceramic resistors there on the shock tower are primarily to keep too much current from burning out the contact points. No points means no resistors means full alternator voltage to the coils! Additionally, you can also eliminate a pair of relays designed to provide full voltage to the coils while cranking - don't need 'em if you've got full power all the time, right?

So, to recap, you get simplicity, reliability, and usually a stronger spark. Who doesn't want that?

 

OOOO, POWER AND SIMPLICITY! I LIKE IT! WHAT STUFF DO I NEED?

OK, you're going to need an 81-85 distributor first. You'll want one from a 12A, since the GSL-SE (13B) distributors' advance curves are different. Make sure your distributor has working ignitors on it (test procedure is in the factory and even the Haynes manual), and you'll want to grab about a foot or 18 inches of the distributor harness from the donor. That'll be the wiring with the connectors for the ignitors, mainly. Failing that, the two terminal connectors used on the ignitors are very common on most imports; you can snag them from wherever you find them. I did! The factory connectors have nifty rubber boots on them, though. you may want to liberate the coils as well, or ourchase an aftermarket coil or coils 9if you buy just one, put it on the leading), since the points-type coils may not be up to handling full voltage. Mazda specs different part numbers for electronic- and points-type coils. Having said that, I'm using one of my old points coils on the trailing, and an Accel Super Coil on the leading. Works fine so far...

 

HOKAY FINE, GOT TH' GOODS. NOW WHAT?

Put it all together! What, you want more detail? Well, all right...

Physically installing the distributor is fairly easy, just be sure you rotate the engine to TDC first, then orient the new distributor the same as the old. Actually, you can skip the TDC thing and just position the rotor on the distributor correctly, but putting the engine at TDC give you a reference in case you forget which way the old dist was pointing. with the engine at TDC, you just set it with the rotor pointing at where L1 would be if the cap was on.

A little more difficult is the wiring, but not overwhelmingly so. The wiring on the electronic distributor is incredibly simple: all it has is +12V ignition to each of the ignitors (and a condensor to reduce RFI) and then the negative trigger out to the appropriate coil from each of the ignitors. That's it. The super-easy method is to run three wires (ignition, leading trigger, and trailing trigger), but I didn't want to chop up mmy factory wiring too badly. I did run a fresh ignition wire (since the points dizzy didn't use one), but I made an adapter harness so that I could use the original coil trigger wires (which also keeps me from having to rewire the tach). I did remove the ceramic ballast resistors on the front of the left strut tower, connecting the coils' plus side directly to the same ignition source as the distributor, which used to be the source for the ballast resistors. I also removed a pair of relays designed to short around the ballast resistors and give the coils full battery power while cranking, but not while running. These two relays are located between the battery and the headlight assembly support.

That's pretty much it. You could splice into the factory wiring rather than making an adapter, but either way, all connections should be soldered!
If you're not making an adapter and/or don't have the plugs for the ignitors here's a couple hints: the ignitor connection terminals are arranged into a "T" shape. The upright of the "T" goes to an ignition source to power up the ignitors, and the top of the "T" is the coil trigger, which goes to the "-" terminal of the coils. The Leading ignitor is the one on the front of the distributor. The coils' "+" terminals should be connected directly to ignition 12 volts, not through the ceramic ballast resistors.
One could leave the resistors and relays (and I did for a while), but one of my goals was to clean up the engine bay. Removing extraneous bits is one way to do that!

dist harness thumbnail

Here's a diagram of the adapter I made

 

Back to Modifications Page