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66 Mustang pink resister wire

tarafied1

tarafied1

Well-Known Member
Another question for the electrical gurus (Mid). I have this 66 Mustang 289. All stock (for now). It sat 30+ years. I just got it running with a carb rebuild, new cap/rotor, points, plugs and wires. The coil was also replaced. I did not change the condenser until second set of points. It will run good for a while then die. I eventually discovered that the plastic rubbing block on the points looked melted and point gap was going away. I replaced points again, this time new condeser as well. Same thing. So I figure I have a problem with points getting hot. Sure enough if I run it a short while, pop the cap, the points are smokin hot. I have it wired the way it appeared to be when it was parked. But I did also have to replace the starter relay (solenoid) and the starter. There is no wire from the solenoid "I" side. Only "S". Anyway, I checked the voltage at the coil + side key on, it's batter voltage. I also disconnected the points and checked coil - with key on and get the same (battery voltage). So my thought is someone bypassed the resister wire at some point in it's life because, shouldn't there be a wire from the "I" side of the relay that's at 12V during start and the coil positive at ~6V when key is in run? My 67 is so modified it is no help looking at it.
 
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Maybe found my issue, or one of them. The ground wire looks pretty sad. Maybe a bad ground. Even with 12v it shouldn't get hot to the touch... If it will stop raining long enough I'll try to clean and/or replace that wire.IMG_7555.jpg
 
Got this schematic from Mach1 Driver (THANKS). What color(s) should the wire from the "I" relay be? And I presume it's the 12v when starting per the schematic so what does the pink wire look like at the coil? Not still pink...

IMG_7558.jpg

IMG_7554.jpg
 
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The I wire is brown.
You'll see battery voltage at the coil with key ON but car not running, as there's no current flowing through the system, so voltage will be high. The way to test for the resistor wire is to measure resistance from BAT to + side of coil with key ON, but engine not running. You should see at least 1.5 ohms. This is not fail-safe, as there can be extra resistance at various connections. Best to measure from pink resistor male plug at ignition switch to the + side of the coil.
 
Midlife said:
The I wire is brown.
You'll see battery voltage at the coil with key ON but car not running, as there's no current flowing through the system, so voltage will be high. The way to test for the resistor wire is to measure resistance from BAT to + side of coil with key ON, but engine not running. You should see at least 1.5 ohms. This is not fail-safe, as there can be extra resistance at various connections. Best to measure from pink resistor male plug at ignition switch to the + side of the coil.
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thanks, I will check that. Do you have a theory on why the points get hot to the touch? I haven't had a chance to fix the ground wire in the distributor yet but I figure a bad ground could cause that. I hope its that easy anyway
 
It sounds like you have too much voltage at the coil. Turn the motor over until the points are closed, turn the key to ON, and read the voltage across the Bat. and Dist. terminals on the coil- it should be between 4.5v and 6.9v. If more than that you have a problem with the resistor wire.
This is from Average Joe Restorations- a good source for free wire diagrams:
1748694852169.png
 
I'm gonna check it tomorrow maybe. It rained me out Friday and today I spent the day with the wife! Thanks for the tips and the diagrams and schematics!
 
That crusty distributor is awful! If I were you (and had your money), I'd replace it.
The 66 engine gauge harness is reproduced by Alloy Metal Products, and is a good buy with good quality. For something like $70, it would be worth it to replace what you have, instead of trying to fix it...
 
Kentucky Mustang and others have the harness Mid mentions for about $40. That is really cheap if you're wanting to keep everything stock.
 
Mach1 Driver said:
It sounds like you have too much voltage at the coil. Turn the motor over until the points are closed, turn the key to ON, and read the voltage across the Bat. and Dist. terminals on the coil- it should be between 4.5v and 6.9v. If more than that you have a problem with the resistor wire.
This is from Average Joe Restorations- a good source for free wire diagrams:
View attachment 36490
Click to expand...
Okay, cleaning the ground didn't fix the heat in the points issue. I unwrapped the harness and coil was wired to key on 12V. "S" terminal was spliced but eventually went to the the 32 red/blue wire. Brown 262 was not hooked up and dead-ended in the tape. I have found the yellow wire going to voltage regulator (655 I guess). I also have the temp sender wire not shown in this diagram but it's red/white. And I think the oil pressure sender was hooked to a white/red wire but not shown here and I'm not sure if that was correct. I also have a solid red wire in the plug but wasn't hooked to anything. I'm gonna hook the relay and coil after I make new wires (harness is butchered). We'll see if the points still get hot to the touch after that. If that fixes it I will buy a new harness as you guys recommend
 
I wired everything as it was supposed to be. No power to the coil + wire or the brown wire when key was in "start". I think that's why the billy rigged it. I'm gonna order new harness and 16A wire. I'm guessing ignition switch might be bad (no power for ignition). It does work the starter.
But I bought a ballast resister and hot wired it so I could drive it at least.
 
655 yellow is the ammeter line, and connects to the alternator harness. 654 red is the other ammeter line and goes to the battery side of the starter solenoid. Be careful with these two wires, as they are always hot and not fused.

Do my resistance check on the pink resistor wire before trying to splice it in. It cannot be soldered and must be butt spliced.
 
Midlife said:
655 yellow is the ammeter line, and connects to the alternator harness. 654 red is the other ammeter line and goes to the battery side of the starter solenoid. Be careful with these two wires, as they are always hot and not fused.

Do my resistance check on the pink resistor wire before trying to splice it in. It cannot be soldered and must be butt spliced.
Click to expand...
I found the pink resister wire is hanging under the dash near the headlight switch unplugged! What is it supposed to be plugged into? If I jumper 12V to it the coil has power at low voltage and car runs fine. There should be a key on 12V source under the dash somewhere...
 
There is a short female bullet with red/green wire coming from the back of the ignition switch. The pink resistor wire plugs into that female bullet.
 
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