28 replies to this topic

[Keith Novak]

Before I put an engine back in, I plan on re-routing the harness from the PPF to the passenger compartment through the AC hole. What do you do with the plugs for the transmission? I'm pretty sure one is reverse lights (don't need) one is the clutch switch for ignition (important), and I forget what the 3rd does.

I'm pretty sure it's in Dave's construction manual that I loaned to a friend who's considering a build.

[Jim Boemler]

I only recall two connections (4 wires total). Never thought about using the AC hole -- what's the point of that? I always thought about re-routing the harness that runs along the PPF, so that it runs along the inside of the tunnel instead. That would make it easier to remove the PPF for trackside clutch/tranny replacements. Never did it, since it seemed legally questionable.

[Keith Novak]

There are 4 connections. 2 plastic connectors and 2 single wires. I figured each multi-wire connector had a separate function and the single wires were both sides to the same circuit. I knew what they did once and since forgot. I'm pretty sure now one isn't the clutch switch so they could be completely unnecessary. Dave W recommends retrouting through the pax compartment for the same reason...easier when you have to pull the PPF for trans or engine. Being on the rule writing committee I'll take his word for it that it's legal even if it doesn't say it is.

The AC hole is right there so instead of going down through the body, along the PPF and up by the bell housing it will be easy and with it not coming up through the gap between the bell housing and the fire wall it seems a lot cleaner install. There's too much stuff in that location any time I have to get in there to do anything. On the 1.8, with the motor a touch larger it's always hard to reach anything under the intake manifold so the easier I can make things for myself the better.

[dstevens]

I was just down there looking at it for the harness reroute. IIRC it's a neutral safety switch. I don't recall the re route being in Dave's book. It's in the shop, I'll check it when I get home. My plan was to extend the trans wiring if needed after i pull back that circuit from the loom. I've got a great split loom source locally (that's what our biz calls convoluted tubing) and I'm re skinning all my harnesses. That for sure will go in the build blog.

[Jim Boemler]

Just checked my spare trans. Four wires total, 2 in a nylong connector, and 2 separate. One set is for the neutral switch, one for the reverse. I have no idea what your third set of connections might be.

[Tom Hampton]

My 1992 / NA FSM says backup light switch and neutral switch.

[Tom Hampton]

From memory one of those switches has two separate pigtails that the wires connect to, instead of a multi-pin molex type.

Clutch switch is under the dash and is actuated by the clutch pedal. Some people disable this switch....so they can start the car without getting in.

The reroute is not in the not in the SM Constructor's manual. It IS in the installation instructions for his electrical cutoff switch kit. Its slick, its easy, and it makes dropping the PPF a piece of cake. +1000.

Edited by Tom Hampton, 05-16-2012 08:24 PM.

[Keith Novak]

You're right. It is 4 wires, 2 spade type with plastic sleeves and 2 that are more a dowel type. What does the neutral switch do? (I could look this up but I'm assembling the bottom end and and poking my head back in from time to time. Call me lazy...I'll admit it freely. )

[Jim Boemler]

I think it's used for the cruise control. I had thought about wiring it so the car would start with either the clutch depressed OR in neutral, but again not completely legal.

[Keith Novak]

Cool. Now that it's legal to remove the cruise control components I guess I don't need either.

[dstevens]

From the looks of the schematic it's telling the ECU you are in neutral. My 90 had no cruise control and it's still there and the diagram shows the CC upstream of the switch on the trans with a capacitor between them. My WAG would be that the ECU wants to know if it's neutral so it can set idle or some such.

[Tom Hampton]

Yep....both the clutch switch and the neutral switch are wire-OR'd into pin 1V on the ECU. So, the ECU knows when the car is NOT connected to the drive line...it doesn't know the difference between clutch and neutral.

The same terminal is connected to the cruise control unit.

[dstevens]

From what I can gather at Miata.net in cars that can throw codes when the switches fail there can be idle issues. Of course if the clutch interlock fails you won't have to be too concerned with idle. To the ECU neutral would be the same as the clutch in.

[Tom Hampton]

I have my clutch interlock disabled and I don't have any idle issues...except when I find a hole in the air intake tubing downstream from the AFM, or a vacuum leak.

[dstevens]

Not the clutch interlock, the one on the trans. These were early 2000s cars and I'd bet the ECUs are WAY different than our 1.6 NAs.

[Tom Hampton]

Ah. Yeah, those ECUs are completely different.

[Glenn]

Why do you guys remove the PPF doing a gearbox change? Just loosten and pull to the passenger side and hold in place with a strap!

[davew]

Sorry I was out of the office yesterday to make a quicker comment.

Glenn, if you are looseneing the PPF why not just get it out of the way completely. Now with a little wiggeling you can get the trans out without removing the exhaust.

I do not recomend rerouting the entire "PPF Harness" through the interior. I do recomend taking the main battery cable out of the harness, cleaning all the goo off and running it through the interior. Taking the goo off is the worst part! I route the small transmission wires along the brake lines still under the car with several zip ties.

The switch with 2 short wires, red on an original switch, green on a replacement, is for the back up lights. If it is not hooked up there will be no issues except the back up lites will not go on. There is no polarity on the wires. The green wire/replacement switch is the original Mazda cure for the "stuck in Reverse" problem. I always put in a green wire switch when rebuilding a trans.

The second switch with the longer leads is a neutral switch. It has nothing to do with starting the car (that would be the clutch switch under the dash). I do not know for sure if it ties into the cruise control or not, but it may. In an unmodified car, the computer will raise the idle when the car is in neutral over being in gear with the clutch pushed. My guess would be that it has something to do with emmisions. For our use, it does nothing.

Both switches can be left disconnected. I do not. It just does not feel right to me.

Dave

[Glenn]

Sorry I was out of the office yesterday to make a quicker comment.

Glenn, if you are looseneing the PPF why not just get it out of the way completely. Now with a little wiggeling you can get the trans out without removing the exhaust.

I do not recomend rerouting the entire "PPF Harness" through the interior. I do recomend taking the main battery cable out of the harness, cleaning all the goo off and running it through the interior. Taking the goo off is the worst part! I route the small transmission wires along the brake lines still under the car with several zip ties.

The switch with 2 short wires, red on an original switch, green on a replacement, is for the back up lights. If it is not hooked up there will be no issues except the back up lites will not go on. There is no polarity on the wires. The green wire/replacement switch is the original Mazda cure for the "stuck in Reverse" problem. I always put in a green wire switch when rebuilding a trans.

The second switch with the longer leads is a neutral switch. It has nothing to do with starting the car (that would be the clutch switch under the dash). I do not know for sure if it ties into the cruise control or not, but it may. In an unmodified car, the computer will raise the idle when the car is in neutral over being in gear with the clutch pushed. My guess would be that it has something to do with emmisions. For our use, it does nothing.

Both switches can be left disconnected. I do not. It just does not feel right to me.

Dave

By loosten I mean CRACK the tension off teh bolts, although most times I forget to and just ratchet it out of the way But then again I do remove the exhaust on most changes. I would rather EFF with thye exhaust than reinstalling those BS PPF frame assemblies

[FTodaro]

Both switches can be left disconnected. I do not. It just does not feel right to me.

Dave

thats ok you saved me 35.00 that i was going to spend to replace the broken wire I have on one switch. I will just skip it and see what happens.