I was getting ready to swap and noticed that the 79 (the shiny one in the photo) has two less electrical connectors than the 80 - one on the bellhousing and one on the tail shaft. It's not even tapped for them. Does anyone know what they do?

note: the middle switch of the 79 is missing a wire; I need to solder on a new one

 

Probably the "4th gear" and "top gear" switches that drive some of the emissions controls. The one they both have would be the reverse switch, which runs the backup lights.

 

can't really say. only one i use and feel really necessary is the one for the backup lights.

 

DD has it right. The two extra ones are there to tell the 80 when to do some nasty emissions stuff like shutdown trailing plugs and so forth. I use them to turn off my efan when I'm in 4th or 5th gear

 

The J-spec swap tranny in my '80, interestingly enough, has only two switches; reverse, and one of the two high-gear detectors (can't remember if it's 4th or overdrive.) Ended up bypassing the other connection with a jumper.

 

When your doing the swap use the crossmember from the 80 transmission because the 79 has a different design and will no fit.

 

I did the measurements:
The front switch's leads (on the bellhousing) are shorted in all gears except 4th, and they're open in that gear. The rear one is shorted in all gears but 5th. The middle one is indeed for backups lights - it's only shorted in reverse. Why they didn't just have it switch to ground and save an extra lead per switch is beyond me (I was really hoping that that one switch was actually two, for the E-FAN hack.).

In doing the measurements, I noticed that the two switches, particularly the one for 5th (the rear one), sometimes got stuck open from the sludge inside the transmission. So for anyone trying to get the stock emissions to work, CLEAN THE TRANSMISSION SWITCHES! Hmmm, maybe my engine going into advance at inappropriate times is why the engine died...

I think at least one of them aides in controlling the trailing ignition vacuum advance for emissions sake. This makes sense since, as stated on page 103 of the Haynes manual and implied on page 101, the vacuum control valve isn't present on automatics or at all on 79's.

On page 85, it mentions that the relief solenoid valve (for Cali 79 models, which is the same for federal 80 models) turns off when the transmission is placed in 4th of 5th below 3krpm and above idle. The relief does something in the air control valve which I'll look up another time.

Finally, the diagram on page 89 shows that it does affect the trailing ignition.

The car probably doesn't differentiate if it's in 4th or 5th. Rather, it was just easier to use two instead of one, particularly to accommodate the 4 speed model.

It's probably best to short out those extra leads in the general case for this swap so the car doesn't always behave likes it's in cruise mode. For my purposes it doesn't affect anything except for doing the EFAN hack. That's a nice hack btw, Tim. I won't be copying it anytime soon since the tranny is already in the car.

DivinDriver - Maybe that transmission was originally a 4-speed? just a guess

 

Those two switches are tied in series with the OEM tranny
wiring harness and you just have to use one plug coming up
under the brake master to hook into it. Easy hack if you have
the oem harness otherwise you would have to make one up.
I'll show you next time we see each other. I basically run my
ground through that series for the efan relays.

 

interesting tim. nice to know there IS another option to controlling the efan. will have to get with u on that sometime.

 

Yep; As T_G mentions, the two switches are wired in series, so there's no way the car can differentiate 4th from 5th.

The history on my trans is that it was a J-car takeout, imported to the US by K Watenabe Corp back in the early 90's. They used to be a great source for used rotary engines & trannies that were taken from scrapped out cars in Japan (mainly due to the hellishly aggressive vehicle inspection laws over there) but perfectly serviceable. A lot of RX-7 racers were regulars there.

It's doubtful that it was modified from 4-speed to 5-speed at that time - - it would have been a whole lot easier to just buy a 5-speed, as parts rarity was not an issue back then - - but I don't have any data on J-spec trans builds from that period, so it's possible. In all other respects it is identical to the trans that came out of my 80 at the time.