I've another research project that I could use everyone's help on

I've a '75 with a 5 speed manual. I'm trying to identify the sensors/switches/electrical items coming out of the trans. Unfortunately nothing seems to fit in the manuals and wiring diagrams I have. I've just ordered a diagram from Midwest so maybe that will have an answer, but figured I'd ask the group

I'm 99% sure this is the reverse switch:


The reverse lights on the car were not working when I started this process so this is obviously something to look into. What's odd is that it looks like the PO replaced the switch with one from a later model? The yellow wire coming out of this wasn't actually hooked up to anything in the car's electrical...

I'm not sure what this one is - it's on the passenger side in the center of the transmission:



It has the numbers 0343 & 8b on it. As you can see the two wires are in tough shape. The ground was attached directly back to the trans (via a terrible slice job), and the positive had a rubber sheath (heat shielding?) on it.

Anyone know that this mystery electrical is?

I'm pretty sure the first one is the reverse switch, however I have no idea why it has three wires. I think I have read somewhere that there was a device to adjust the idle in neutral or when switching between some gears, maybe that's it.
The second sensor seems to have been added on later, isn't that the location of the fill plug for the transmission? Maybe it's a level sensor to monitor the fluid level in the transmission...

Is it possible that this transmission isn't the original for your '75 spider? Given the hack job on the ground wire, and the fact that things look odd, I'm guessing that someone changed some parts around.

Yes, the first switch (the one with three wires) is the switch for the backup lights, and it engages when the transmission is put into reverse. I'm also mystified why it has three wires, unless it's from a different model transmission. Maybe from an automatic transmission? From some wiring diagrams I have, the backup switch has one blue/white wire and one white wire.

The second switch (with the numbers you quoted) is part of the emission control system, and the switch is engaged when certain gears are selected (3rd and 4th if I recall). On earlier cars, this switch controlled the fast idle electrovalve which is located on the driver's side of the engine compartment up towards the top and somewhat towards the rear, with one vacuum tube leading to the intake manifold and one vacuum tube leading to the carburetor. On later cars, I believe this transmission switch was still there but instead controlled some aspect of the Exhaust Gas Recirculation (EGR) system. I'm not sure where a '75 spider lies between these two options.

In summary: First switch is the backup light switch, and the second switch is part of the emission control system.

-Bryan

I had this question on these same sensors when working on my ‘78 spider, which has 5 spd manual. For starters, go download http://www.njfiats.org/joomla/images/st ... Spider.pdf. This is the electrical diagram by Brad Artigue for '78 spiders. NJfiats.com is a site with a great wealth of information. They have a wire diagram for '76 model as well, but not '75. Anyway, the '78 diagram has the very switches you show.

Next, I mapped out what the switches do and found them in the referenced electrical diagram...

The switch on the side of the tranny is a simple 2 wire, black goes to ground and grey has spade connection. This switch is normally open, and closes when in 3rd or 4th gear. It is switch #192 on page 4 of referenced '78 electrical diagram. It is one path to activate the 190 fast idle electrovalve on the carburetor (I have ADFA carb)... that is when in 3/4 gear AND clutch pedal is disengaged. Note with age on wires, you will have to use a lot of imagination to match the colors.

The switch on the rear of the tranny is dual purpose, switch #25 on page 3 and 4. The light blue wire is a common 12V supply. The common makes contact with the white wire when in reverse (to power backup lights as stated earlier) and the red wire when in 5th gear (drive EGR bypass electrovalve 190/2). Though I suspect the '75 does not have EGR, so as suggested earlier, likely from a different car. My car has the red to a 1 pin connector, and the other 2 to a 2 pin connector, as shown in your picture.

I have some picture notes that explains it better than words, but I could not figure out how to upload pictures easily, though I see it can be done. If anyone can help me with that, I can upload my pictures.

I hope that helps!
David

DustyDave wrote:I have some picture notes that explains it better than words, but I could not figure out how to upload pictures easily, though I see it can be done. If anyone can help me with that, I can upload my pictures.

David, I think you have to upload your photos to a third party site (imgur, Google photo, smugmug or the like) and then provide a weblink to that. The advantage is that the server that hosts the FiatSpider site doesn't have to use a lot of memory to store pictures, but the downside is that if the link is broken or the third party picture hosting site goes out of business, your pictures won't appear on the FiatSpider forum.

-Bryan
PS: Thanks for correcting some of my earlier information on these switches. Learn something new every day with Fiats!

Thanks so much everyone for the great information! I'll have to deep dive the wiring PDF linked and take a look at the other wiring diagrams that are in the mail... Considering everything emissions related was gutted by the PO I'll have to see if I even have wires to hook that up to. Time to dig around the interior wiring and see what's left.

For image hosting I personally use Github, however you could look at just putting images up on Dropbox or similar as well.