Trivia question of the day

J

John Barbieri

True Classic
What is the purpose and function of the yellow wire with the red stripe in this pic? Hint, it connects to its own terminal on the starter on my carburated 79 1500 and traces into the wiring harness coming out of the firewall.
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If it connects to a spade terminal on the starter then it's the signal wire that tells the starter solenoid to engage the starter. The ones on my Xs are usally just red but we know how Fiat loves to follow their own wiring diagrams.
 
carl said:
If it connects to a spade terminal on the starter then it's the signal wire that tells the starter solenoid to engage the starter. The ones on my Xs are usally just red but we know how Fiat loves to follow their own wiring diagrams.
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No, as you can see, it does not have a spade connector, it's a small rubber elbow grommet like a mini spark plug boot and pushes onto its own terminal on the starter solenoid. There is a spade connection on the lower side of the solenoid for the trigger and its a green wire.
 
John Barbieri said:
No, as you can see, it does not have a spade connector, it's a small rubber elbow grommet like a mini spark plug boot and pushes onto its own terminal on the starter solenoid. There is a spade connection on the lower side of the solenoid for the trigger and its a green wire.
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This powers the gulp valve thermoswitch as part of the emissions system. You can see it on this part of the wiring diagram (page 1 on Mira)

This is a peculiarity of the early carb 1500s.
1979
CDFE8CD2-6CB5-4D98-9238-8E3A2AC1EC97.jpeg

1980 (carbed)
43C86D28-BAAE-49B6-A97B-2B709744457A.jpeg
 
kmead said:
This powers the gulp valve thermoswitch as part of the emissions system. You can see it on this part of the wiring diagram (page 1 on Mira)

This is a peculiarity of the early carb 1500s.
1979
View attachment 23681
1980 (carbed)
View attachment 23682
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Not on mine. This wire goes into the wiring harness, back into the cabin somewhere and powers my instruments and all my accessories while the key is in the start crank postion and it isn't the same color as any of the wiring diagrams I've seen.
 
I would look at the connections from the other direction, where does the instruments intersect the white with red wire.

I suspect the issue is around fuses 1 and 2. Of course I am just as likely wrong :)
 
Maybe the PO made the same mistake you did thinking this is a yellow/red wire and not what it really is, a white/red wire. I don't have a 79 wiring diagram, but on my '86, yellow/red wires power the switchgear lighting....if you get a '79 diagram and yellow/red wires power the switchgear and/or instrument lights, maybe we got a smoking gun; maybe the PO grafted this wire into the instrument panel lighting circuit?
 
I just looked at my '79 carb model's starter again to be sure. No such wire goes to the starter. There are the two large cables (battery and alternator) on the large threaded post, and a red wire that push-connects to a blade terminal. That's it.

I'm thinking if your dash only works during cranking, then attaching that red/white (white/red) wire to the starter was the problem. That connection to the starter is only hot during cranking. So I would guess the wire in question should attach to a constant "switched" source to power your dash any time the key is "on".
 
That wire and connection are on the wiring diagram, I don’t know about the connector. I would think the wire originally was connected to the same exciter wire for the starter main post not the starter solenoid. Which means it is always hot. I suspect there is some other nefarious wiring around the gulp valve thermoswitch and the rest of the running circuits.

Given the push on of the connector it should just go onto the main stud of the starter not the solenoid.

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kmead said:
I suspect there is some other nefarious wiring around the gulp valve thermoswitch and the rest of the running circuits.
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The wires for things like the gulp valve, carb cooling fan, and such are very bizzare on this car. They have all sorts of really odd connections and routing. For example one lead (don't recall which of those it was for) went from the source, around the engine bay, through the firewall into the cockpit, looped back around with no connections, back through the firewall again to the engine bay, and connected to something else near the source. Another example is the orange wire; it connects to a bunch of totally unrelated stuff, just branching after branching after branching. Or the one to the AC compressor that goes from the hole in the firewall to the drivers side and near the rear trunk before looping back up to the firewall and then to the passengers side before going back to the compressor. And sooo much more. After removing all of the harness covers and separating every wire I was shocked at how many miles of excess wire I was able to eliminate when simplifying all of it. Also eliminated a bunch of unnecessary and faulty connectors. And while I'm bitching about X1/9 wiring harnesses in the engine bay, why are there so many separate holes through the firewall with bundles of wires? Why not pass ALL of them through one hole to eliminate the extra leaks, and add master connectors to make servicing easier? I swear, most of the harness had to be built on the car, installing attachments after routing, so they cannot be removed without cutting things.
 
Consider the time. Master connectors were years in the future after the X was no longer made. VW went to them in 1993 on the A3 series cars.

As for the routings and extra wire I wasn’t in the meeting at the time but I know the type of people who make that sort of thing happen.
 
Isnt the wire to the oil pressure dummy switch red and yellow? Also that would match the elbow rubber piece on my '78.

Edit. The OEM 78 wiring diagram shows that as yellow gray but I could have sworn it was red/yellow was I changed the grommet from a female spade to connect to my new VDO sender.
 
Looking at the wiring diagram, the red-white wire is bypassing the thermoswitch when the motor is cranking: It's powered only when cranking, and it is connected to the opposite side of the switch from the key-on 12v. The effect is that the car always acts as if the thermoswitch is closed when it is cranking, no matter the engine temperature.

Also looking at the '79 wiring diagram, the instruments that were not working properly are not powered directly through fuse A (key-on switched power). They are powered off of the seat belt alarm system (we have already mentioned that the '79 1500 has many strange and wonderful eccentricities) which is expected to behave differently when cranking and when running. I expect that that has a lot to do with the original problem.

Dr.Jeff said:
I just looked at my '79 carb model's starter again to be sure.
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Not completely surprising to find a '79 that doesn't match the '79 wiring diagram. Very few changes exactly correspond to the model year, especially in the early years before the design details stabilized.
 
I believe I posted about that post on the original starter a few years back and it is indeed a controller for the gulp valve as noted by kmead. When the starter is engaged the solenoid completes a circuit that keeps the gulp valve closed. Once the starter is released, so is that circuit and the gulp valve can function normally. Whether the colors on the wire are correct or not is another matter. But that socket head connector is the giveaway. Useful device for those of us with fully functioning emissions equipment. The deal is that I had to get innovative when I replaced the original starter with a gear reduction starter and there is no source on the new starter to supply that wire the necessary voltage.
 
Hi Larry,
I just installed a mini starter in my '79 X 1/9. I left the white/red wire unplugged, the car started fine and ran without issue during my test drive. Your thread said that you got innovative when you installed the Gear Reduction Starter. Please let me know if you believe there may be a problem with this wire disconnected and how did you create an innovative work-around.

Thanks,
Tommy
 
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