C325 questions

[Tarheel Blue]

Now that the old 300 is out of the bay, I thought that I’d take the opportunity to tidy up things a bit. I have been diagnosed with a very severe case of the “while I’m in there, I might as well” desease!

Thanks to Jeff’s post about the C322 connector and the other two, C321 & C323, I’ve decided to make all new mini harnesses to all of the connections between the firewall and the engine. That brings me to something that I can’t stop wondering about.

C325 connects the firewall harness to three things on my engine;

+ side of the coil

Oil pressure sensor for the gauges

Water temp sensor for the gauges

What I can’t seem to get my head around is that the R/LG wire on the harness side is LARGE

I’m guessing AWG 10? And then on the engine side of C325 the R/LG is more like a 14-16 AWG

Why?

I’m used to sizing wires in residential construction based on anticipated amperage. If that thinking carries over to automotive DC wiring, then Ford must have imagined a large load on that R/LG wire. But then they connected it to a MUCH smaller wire @C325.

As long as you’ve read this far I’ll ask another question. I’ve seen mentioned that the EVTMs and the wiring diagrams (schematics) indicate color/ circuit/ wire size.

I’ve never been able to see ANYWHERE an indication of wire size. Am I missing it somewhere? Has anyone else ever seen wire size?

 

[ArdWrknTrk]

You need to look in the front of the book.

If you don't have a physical copy, I can't recommend enough that you find a used one on eBay for around $25.

Evidently I'm going to have to pull up the '85 and paste the pertinent pages in this thread.

That might take a while but I should have time on the overnight.

[Tarheel Blue]

You need to look in the front of the book.

If you don't have a physical copy, I can't recommend enough that you find a used one on eBay for around $25.

Evidently I'm going to have to pull up the '85 and paste the pertinent pages in this thread.

That might take a while but I should have time on the overnight.

Thanks Jim,

I’ve had a physical hard copy of the 1985 EVTM as well as the factory service manuals builders book, c size prints of the schematics, etc. for years now and that’s probably where it says that gauge is indicated. I just have never seen a demarcation that would indicate gauge.

[viven44]

Is R/LG the one that goes to the coil positive ? I wonder if the larger gauge wire is part of / continuation of the resistance wire. Also, is there actually more conductor or just more insulation ?

[Tarheel Blue]

Is R/LG the one that goes to the coil positive ? I wonder if the larger gauge wire is part of / continuation of the resistance wire. Also, is there actually more conductor or just more insulation ?

That’s an interesting question, but I don’t know yet as I’ve not snipped it off at the connector. Might should do that in the morning. And yes, it connects to the much smaller wire that ends at the coil horseshoe.

[viven44]

That’s an interesting question, but I don’t know yet as I’ve not snipped it off at the connector. Might should do that in the morning. And yes, it connects to the much smaller wire that ends at the coil horseshoe.

Well, that snipping is sort of irreversible, I am not sure you need to do that :) Those old wires don't like to be soldered back, and you will need to use heat shrink crimp fitting to get it back together.

My best guess is that it is one of the idiosyncrasies of the wiring.

If you have a current clamp meter, might be a good idea to see how much current is flowing through the positive coil R/LG wire while running.

[ArdWrknTrk]

Well, that snipping is sort of irreversible, I am not sure you need to do that :) Those old wires don't like to be soldered back, and you will need to use heat shrink crimp fitting to get it back together.

My best guess is that it is one of the idiosyncrasies of the wiring.

If you have a current clamp meter, might be a good idea to see how much current is flowing through the positive coil R/LG wire while running.

https://forum.garysgaragemahal.com/Pre-Emptive-FIRE-tp58908.html

 

[viven44]

https://forum.garysgaragemahal.com/Pre-Emptive-FIRE-tp58908.html

Thanks. That’s a good recall of that wire being discussed… So it does look to be the resistor wire or at least an extension of it. Also.. the reason for the heat on it is power dissipation through the resistance wire, and therefore a bit more insulation to keep things protected? That makes it look like a lower gauge wire.

[ArdWrknTrk]

Thanks. That’s a good recall of that wire being discussed… So it does look to be the resistor wire or at least an extension of it. Also.. the reason for the heat on it is power dissipation through the resistance wire, and therefore a bit more insulation to keep things protected? That makes it look like a lower gauge wire.

I think it's almost like a fusible link, with an insulation that won't burn.....

[ArdWrknTrk]

Thanks. That’s a good recall of that wire being discussed… So it does look to be the resistor wire or at least an extension of it. Also.. the reason for the heat on it is power dissipation through the resistance wire, and therefore a bit more insulation to keep things protected? That makes it look like a lower gauge wire.

Total recall, it's my Superpower! 🤣