Wiring Question -- Which Wire?

[Dustang83]

I just made a discovery tonight. The wire that I currently have connected to the Red/Lt Green wire going into the main harness (through the driver's side firewall) is reading only 11.4 volts while the engine is running. I traced the wire back to the key cylinder, and it actually has a 1.1kohm resistance built into it. Keep in mind this is in my 1980 Fairmont Futura. I am wondering if the Red/Lt Green wire going into the main harness requires this resistor to be inline with it, or can I hook up a different wire that I tested reading 13-14V at idle. From what I understand this wire powers the TFI module, and also the ignition coil, so I don't want to hold back voltage to them unless they require it. I would appreciate any input, thanks
-Dustin

 

[HISSIN50]

Dustin, one of the old(er) timers like JRichker will be able to say better, but I believe that Ford has used that wire color for the alternator switch wire forever. This might be part of the circuit you're seeing (though I need to check schematics because I thought the alt wire was of small gauge - smaller than anything going to the Ignition itself. There might be a tee with a smaller tributary splitting off however).

On the alternator aspect: Fox and SN mustangs have a 500 Ohm resistor built into this wire (in parallel) in case the battery light burns out (the regulator is on the far end of the wire, and supplies ground when the alt is not excited, and removes ground when the alt excites). On your older car, this could be a similar situation.

Just an idea for your or someone else to agree with or refute.

Good luck.

 

[Dustang83]

HISSIN,
Thanks for the reply. That's a good call on the alt switch wire. I've been studying several schematics for a while now and the wire that you're describing is Light Green/Red instead of Red/Light Green. Don't know why Ford made them so confusing, but anyways... I have that wire already connected correctly with the required inline resistance. The charging system is working properly for me.
I wish I still had my donor car here so I could just pop a multimeter on the Red/Lt Green to answer my question lol Any other ideas?

 

[HISSIN50]

Actually, that alternator wire is both colors. I have the sinking suspicion it and the TFI wire you're looking at are one in the same at the ignition switch.

You probably have been looking at them already but just in case:

alternator wiring and ignition switch wiring

Good luck and bump for ya Dustin.