Yet Another Engine Fan Post

[18Fiatsandcounting]

Yes, pictures would help here. I'm thinking something shorted out many moons ago, and the previous owner tried to rewire things but didn't quite get it right. The large pink wire is where a lot of the +12V connections come through, so if that is goofed up, you'd have all sorts of weird things going on.

Other than the horn and the fan, anything else not working? Lights? Hazard flashers? Wipers? Heater fan? Etc?

-Bryan

[CharlieB]

Surprisingly everything else seems to be working.
Please excuse my mess.

The small orange connector is the issue. The wiring diagram shows the gray/red wire going to the mysterious tachimetric switch, which I don't think I even have.
Thanks Bryan

[18Fiatsandcounting]

The wiring diagram shows the gray/red wire going to the mysterious tachimetric switch, which I don't think I even have.

I have to admit I never understood the tachimetric switch, although I have heard people referring to it. In a wiring diagram that I have, the tachimetric switch is connected to both the tachometer "sensor" connection to the coil, and to the idle stop solenoid. I really don't know what it does.

If it helps, the wiring diagram I have for this tachimetric switch is wired as such:
Blue, which looks to be the +12V from Fuse 9
Black/purple, which looks to be a ground
Brown/white, which goes ultimately to the brown wire for the tachometer sensor (ignition coil)
Grey/red, which goes to the idle stop solenoid on the carb
White/black, which goes to an idle stop switch but only on California cars.

-Bryan

[CharlieB]

Thanks Bryan,
It sounds like your wiring is a little different than mine, but same concept i guess.
So I'm trying to decide what to do with this corroded wire as far as replacement. Can I just remove it all together and not replace it? it doesn't seem to do anything, on my car anyway.
The large pink wire appears to be intact.
I have never had the idle stop solenoid plugged in and as far as i can tell, it has not had any ill effects.
Thanks,
CB

[18Fiatsandcounting]

I have several different wiring diagrams for the mid 70s, so no guarantee that what I'm seeing matches what you have. Heck, my diagrams don't always match each other sometimes....

Since this corroded wire doesn't seem to be harming anything, and everything except the fan and the horn appears to work, I would leave it be for now.

By the way, I think (think being very tenuous) that the tachimetric switch controlled the idle fuel circuit on the carb. You of course want the idle circuit to be active when idling, but there may be some other conditions where you want some flow of fuel into the engine for emissions purposes. Like when you have the engine at high revs and completely let off the throttle. That can lead to backfiring and a spike in the NOx emissions, so maybe the tachimetric switch turns on the idle circuit to avoid that?

Pure conjecture on my part, but hey, that's all I got for you at this point!

-Bryan

[CharlieB]

Bryan I think you're right. I need to stick with the task at hand, getting the fan and horn sorted.
I'll go through everything again over the next couple of days and see what's going on.
When I get those figured out, it would be nice to have an idle cut off solenoid that actually works.
Thanks
Charlie

[CharlieB]

Well I now have an operating fan and horn. I pulled all of fuses out 1 by 1 and scrubbed the contacts with sandpaper. I also replaced some dodgy wires at the alternator. Cleaned up a couple grounds and now everything is working like it should. I'm not really sure what exactly fixed the issue but I'm just glad everything is working.
So, I still need to o deal with this corroded wire. It sizzles when I turn the ignition on. Replacing the wire is easy, I just don't know that I even need it. I'll address that tomorrow. For the moment I'm going to bask in the glory of irritating my neighbors with my Fiat foghorn.
Thanks for the guidance with this guy's.
Charlie

[18Fiatsandcounting]

Awesome Charlie! Yes, sometimes contacts (and fuses) look OK, but they develop a transparent corrosion film on them that isn't conductive. So they look OK but don't work. Aluminum oxide is one of those beasts, and I don't like aluminum wiring for that reason. Aluminum is conductive, but the transparent oxide is an insulator. The work of the devil, I tell you....

And yes, we need to look at that sizzling wire. Not good. I thought it didn't go anywhere, but maybe it's got a short to ground? Perhaps just remove its connection at the fusebox and see what that buys you? At least it should stop sizzling!

-Bryan

[CharlieB]

Bryan my description of the corroded wire was confusing at best, sorry.
Here is a picture of the wire still connected at the fuse panel. It is connected at the same terminal as the larger pink wire.
From the fuse panel it runs of the the inline fuse you see in the photo. Returning from the inline fuse it runs through the firewall and connects to C4. From C4 it connects to nothing, its just a bare end wire. The Gray/Red wire from C4 has a female fitting on both ends. 1 end goes to the idle stop solenoid (which has not been plugged in for the past 6 years at least) and the other end is unplugged and is resting near the coolant overflow tank.

And here is the relevant wiring diagram.

I'll work on it later today and see what happens.
Thanks,
CB

[18Fiatsandcounting]

OK, I see. Since you no longer have a tachimetric switch and a functioning idle stop solenoid, and it appears that this smaller (sizzled) pink wire was for those, I'd be inclined to just disconnect it.

Is the wire currently "sizzling", or are you just looking at the evidence of what happened in the past? Maybe this tachimetric switch or solenoid went bad, fried the wire, and so the previous owner just disconnected everything?

-Bryan

[18Fiatsandcounting]

PS: I *think* the tachimetric switch is located in that tray of relays that is mounted under the glovebox. This switch should have 5 wires to it: white/black, grey/red, brown/white, black/violet, and dark blue. (variations may exist) If you find those 5 wires, that's where the switch would have been (or still is).

-Bryan

[CharlieB]

Bryan,
When I turned the ignition to "on" there was a faint sizzling sound.
I'll disconnect that wire and report back.
Thanks,
CB

[18Fiatsandcounting]

OK, understood. Is there a fuse in that red inline fuse holder? If so, I'm kinda surprised it didn't blow, unless the short is not through the circuit that goes through that fuse.

Yes, disconnect that sizzled pink wire and let's see what that buys you.

-Bryan

[spider2081]

I'm kinda surprised it didn't blow, unless the short is not through the circuit that goes through that fuse.

I don't think the overheated wires are fused by the inline fuse. In fact I don't think the pink wires that overheated are fused at all.
A black wire from the alternator output post is connected to the batteries + post at the starter solenoids battery terminal. Another black wire at the alternator output post connects to the ignition switch terminal 30/1. when the ignition switch is in the "start and on" positions ignition switch 30/1(black wire) mates with terminal 15/54 (pink wire) This wire connects to the top of fuse 9. There are 2 pink wires in this single spade connector. One is the one mentioned from the ignition switch the other is to the inline fuse holder 28/4. This in line fuse is for the electric fuel pump circuit. One end of the in line fuse holder has 2 pink wires. One comes from the mentioned terminal at fuse 9 the other goes through the fire wall to connector C4. C4 mating connector is simply a jumper connecting the pink wires to the gray/red wires. C4 has 2 wires in each cavity. 2 pink wire and 2 gray/red wires. The gray/red wires do not look over heated so I think they can be ignored. The pink wires look over heated so I think this is the path with the issue. The pink wire is shown going to the "Thermostatic switch" This switch is used to control the distributor dual point relay. If the ignition system has been modified to a single set of points or electronic ignition the relay and thermostatic switch are no longer used. Disconnecting/removing the pink wire from fuse 28/4 that goes to C4 should have no effect on the engine operation. Installing a new wire to replace the overheated pink wire from the top of fuse 9 to the inline fuse holder 28/4 should be done. 28/4 is the electric fuel pumps fuse and the pink wire is the power feed for that fuse.

[18Fiatsandcounting]

I'm kinda surprised it didn't blow, unless the short is not through the circuit that goes through that fuse.

I don't think the overheated wires are fused by the inline fuse. In fact I don't think the pink wires that overheated are fused at all.

I see what you're saying and mostly agree with it, but I was thinking if something like the pink wire to the fuel pump were to short to ground, current would go through the ignition switch, to one end of Fuse 9, through the overheated pink wire to fuse 28/4 for the fuel pump, and then to the ground short wherever it happened to be. My puzzlement is how could you get enough current flowing through that fried pink wire to cause the insulation to peel off, yet not blow fuse 28/4, or fry the ignition switch?

That fried pink wire is pretty beefy, so there must have been a fairly hefty current flowing through it. At least 10 amps for a fairly long time I would guess based on size, and other than the starter motor, there's almost no single device in the car that would draw that kind of current for any significant time, except for a ground short.

It would be worth checking inside that red inline fuse holder (28/4) to make sure someone didn't replace the fuse with a bolt or the like. Stranger things have happened....

-Bryan