Under hood wiring. - Vintage Mustang Forums
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post #1 of 18 (permalink) Old 07-30-2019, 04:15 PM Thread Starter
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Under hood wiring.

I purchased a new harness for the headlight,horn, and signal lights. It starts at the plug where the master cylinder is and runs around to the starter solenoid. At the end of the cable is a yellow wire and a black wire with yellow stripe. In addition there is another yellow wire that is by itself with a male plug end. Does anyone know where these wires go? The old harness did not have this.
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post #2 of 18 (permalink) Old 07-30-2019, 05:01 PM
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If my memory isn't failing me...

YEL/BLK - Battery side of Starter Solenoid
YEL (ring terminal) - Battery side of Starter Solenoid
YEL (male bullet) - Ammeter feed. Should be a matching wire in the alternator harness.

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post #3 of 18 (permalink) Old 07-30-2019, 05:10 PM Thread Starter
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Got it, but there was not a matching wire in the alternator harness. Should I cut and splice it in somewhere?
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post #4 of 18 (permalink) Old 07-30-2019, 05:22 PM
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Got it, but there was not a matching wire in the alternator harness. Should I cut and splice it in somewhere?
For now I'd insulate the end and find out what doesn't work. If it had a FEMALE bullet I'd say it might be for a radio noise suppressor but you said it is MALE. Do you have an ammeter or alternator warning lamp?

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post #5 of 18 (permalink) Old 07-30-2019, 05:35 PM Thread Starter
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I have the ammeter. If the gauge doesnt work then I know to hook it up somewhere on the alternator.
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post #6 of 18 (permalink) Old 07-31-2019, 10:20 AM Thread Starter
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I mentioned that there was not a corresponding female end. There is one but it comes out of the voltage regulator. It has a tag that says that this for radio suppressor only. But the yellow wire with the male end is hot since it is on the battery side. Any ideas? One more thing, can you wire the NSS backwards? I have power everywhere except, no crank. There is power at the plug on the ignition switch, bit nothing going to starter. Any ideas on this one.
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post #7 of 18 (permalink) Old 07-31-2019, 10:32 AM
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I have power everywhere except, no crank. There is power at the plug on the ignition switch, bit nothing going to starter. Any ideas on this one.
"No crank" suggests the starter relay is either not working or not being engage. When you try to start, is there power to the "S" terminal of the starter reply?
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post #8 of 18 (permalink) Old 07-31-2019, 12:57 PM Thread Starter
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I have power to the yellow wire on the back of the ignition switch. There is power on the battery side of the solenoid. The I terminal on the solenoid has power when holding the key in the start position. No power going to the starter. Replaced the solenoid and same thing. I was looking at the plug for the ignition switch. I should be able to jump the power wire to the wire that goes to the coil and back to the solenoid. Still nothing. This is a new wiring harness and I cant see the metal tabs that plug into the switch. I beginning to think the switch is not engaging the solenoid and the starter. The old plug I took out, you can see all the metal clips that the switch slides into. And before you say hook the old switch back up, the wires are too short. In one of my stupid moments I cut one wire way to short. Would this keep the engine from firing? It will start will my remote starter.
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post #9 of 18 (permalink) Old 07-31-2019, 01:40 PM
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I have power to the yellow wire on the back of the ignition switch. There is power on the battery side of the solenoid. The I terminal on the solenoid has power when holding the key in the start position. No power going to the starter. Replaced the solenoid and same thing. I was looking at the plug for the ignition switch. I should be able to jump the power wire to the wire that goes to the coil and back to the solenoid. Still nothing. This is a new wiring harness and I cant see the metal tabs that plug into the switch. I beginning to think the switch is not engaging the solenoid and the starter. The old plug I took out, you can see all the metal clips that the switch slides into. And before you say hook the old switch back up, the wires are too short. In one of my stupid moments I cut one wire way to short. Would this keep the engine from firing? It will start will my remote starter.
Hummmm..
The ignition switch start wire (not sure the color in your year Mustang or the harness you have) is connected to the S terminal on the starter relay. It energizes the relay, connecting the battery to both the big terminal going to the starter and the I terminal going to the coil (to bypass the resister wire). Do you have the S and I terminals wired backwards? If the ignition switch wire is connected to the I terminal nothing will happen.
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post #10 of 18 (permalink) Old 07-31-2019, 02:01 PM Thread Starter
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No, I have a brown wire going to the I terminal on the solenoid. A red with blue stripe going to the S terminal. With key in start position I have power at the I terminal. But nothing going to the big post that feeds the starter. The ignition switch has a yellow wire that runs to the battery side of the solenoid. This is what I meant about starter wire. If I have read the book correctly, this wire from the battery energizes the switch, so when turned it will send power to the other side of the solenoid to turn the starter. If I have something hooked up wrong, I have no idea what it would be.
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post #11 of 18 (permalink) Old 07-31-2019, 02:17 PM Thread Starter
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One more thing. Would the NSS stop it from cranking? I dont know how I could have it wired wrong, but knowing me I probably did.
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post #12 of 18 (permalink) Old 07-31-2019, 03:24 PM
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One more thing. Would the NSS stop it from cranking? I dont know how I could have it wired wrong, but knowing me I probably did.

of course it would, that is it's job.
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post #13 of 18 (permalink) Old 07-31-2019, 03:46 PM
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No, you can't wire the NSS backwards...it's a simple "on/off" switch.

I'm guessing that you're checking for voltage at the "I" terminal with the BROWN wire still connected? That would be a back-feed from the coil+.

No juice to the "S" post would indicate that either the NSS is interrupting the signal from the ignition switch or you have an open somewhere else. The ignition switch "S" terminal should be "HOT" with the key in the "START" position. If so, then your problem lies between there and the solenoid "S" post.

One thought.... you DO have an automatic transmission, right?
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post #14 of 18 (permalink) Old 07-31-2019, 03:50 PM
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No, I have a brown wire going to the I terminal on the solenoid. A red with blue stripe going to the S terminal. With key in start position I have power at the I terminal. But nothing going to the big post that feeds the starter. The ignition switch has a yellow wire that runs to the battery side of the solenoid. This is what I meant about starter wire. If I have read the book correctly, this wire from the battery energizes the switch, so when turned it will send power to the other side of the solenoid to turn the starter. If I have something hooked up wrong, I have no idea what it would be.
Power to the "I" terminal could be the result of a wiring problem ... remember it is the "S" terminal of the starter relay that energizes the relay and connects the battery to the starter (creates a connection between the two large lugs on the relay). So, with key in start see if there is power to that terminal. If not, you need to "follow the connection" from the ignition's start terminal to the relay to see why it's not getting to the relay's "S" terminal.

Also, just connect a jumper from the battery positive to the "S" terminal and see if the engine cranks then. That will tell you if the relay is good.
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post #15 of 18 (permalink) Old 07-31-2019, 03:53 PM
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PS @Woodchuck is correct. As the brown wire to the "I" terminal is connected to the + of the coil, it will have voltage whenever the coil has voltage.
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