Ignition wired backwards
 

I think the ignition in my '79 may be wired backwards. The Trailing wire from the distributor is running to the leading coil, and the lead wire runs to the trailing coil. I checked the timing for the first time today, and trailing fires well before leading. Leading is right on the yellow mark, trailing, which should be on a red mark past leading, is about that distance in the other direction ahead of leading. Both of the adjusters are as far retarded as they will go.

The thing is, it runs fine (doesn't sputter or stumble or anyway), and has for a couple years. I just never bothered to check timing since I didn't have a light (the previous owner replaced the plugs and wires, I just assumed they did it right since I didn't have obvious problems).

Would it do any damage if I switch the two wires and it isn't actually wired incorrectly right now?

Looking at the wiring diagram, I think the coils are wired normally. The one closest to the front of the car has a yellow wire with a red stripe, the one closer to the driver has a yellow wire with a green stripe. The diagram says red for trailing, green for leading. The 'T' wire out of the distrubutor currently runs to the rear coil, which I think is leading:

https://cimg1.ibsrv.net/gimg/www.rx7...2340215da5.jpg

Ah, points. So many opportunities to run crappy. :)

This system had semi-firing trailing so the tach wire had to be hooked up to the leading coil.

The trailing coil is supposed to be in the front hole. It prevents the high tension leads from having to cross over each other before they get to the cap. Though from your picture it is a little bit hard to tell under the coiled cord from your timing light (I'm assuming).

Yes, the wires do cross over each other there. Far left wire on the distrubutor, labeled T, is running to the rear coil. It's possible the previous owner swapped all of the wires so that the leading position acts as trailing and vice versa, right?

Mostly I'm just wondering if I switch the two wires so they don't cross, what's the worst case scenario? No start, running poorly, or something worse like knocking, detonation, or damaging the engine some other way?

You're not boosted so that eliminates at least half of any potentially engine damaging problems caused by incorrect timing. In other words, set it all the way it should be from the factory and try it out. Using your timing light, you can set the dizzy to the correct place to get the L mark on the pin. Then of course adjust the trailing vacuum diaphragm slider until the T mark lines up. If this runs really crappy for you, it could mean you've got other problems lurking about.

Hmm, has your engine been rebuilt? It is possible that the dizzy drive gear located on the eccentric shaft has been installed backwards. This happens from time to time (I've never done it) and can wreak havoc while trying to get your timing set, leading to a lot of confusion and frustration.

Well, that was it. I switched the two wires and it started right up. I was able to get the timing for both leading and trailing right on the marks, and while it isn't a huge improvement, it doesn't backfire coming down from high RPM anymore and seems to coast at really low RPM a little better.

Gave myself a big scare the first time I tried to restart it though, I hadn't gotten one of the wires reconnected all the way and it shorted against something, thought I'd killed my whole electrical system.

Still surprises me that it ran just fine for 4000 miles with crossed wires and effectively no trailing plugs, I guess they must've been firing too early to have any impact on how the car ran. Just another example of 'don't trust the guy you bought the car from' (or in my case, one of the three owners it passed through after being taken out of long term storage).

Oh, and I'm pretty much positive the engine was never rebuilt. It only has 80k miles and I just replaced what I think was the original air pump belt earlier this week.

I'm glad you got it working!