1979 F100 ignition switch wiring diagram positions?
 

Can anyone tell me what color wires go to which post on the back of the ignition switch? I have the following wire colors:

a. purple / white = to low brake switch
b. red / blue = to NSS
c. red / green = to instrument cluster lights
d. black / green = to instrument cluster, alternator and throttle solenoid
e. yellow = courtesy lights and hazards
f. black / green = radio, back up lights, wipers, accessories, directionals and to blue wire on column harness
g. orange = to heater

I have the following positions on the key switch:
1. Batt
2. Batt
3. Acc1
4. Acc2
5. Ign1
6. Ign2
7. ST
8. P1
9. P2

BATT is hot-at-all-times feed from the battery, which should be YELLOW. The YELLOW wire that goes to the back of the ignition switch should be very heavy gauge as it feeds the entire electrical system of the truck. I'm not sure if this is the case for '79, but I've seen applications where two thick wires go to both BATT terminals of the switch.

ST is hot-in-START and feeds the RED/BLUE wire to the NSS - which then feeds the 'S' post of the solenoid.

P1 and P2 are prove-out - meaning they are designed to ground out certain warning light bulbs when you turn the key, to let you know the bulb is out. Otherwise the only way to know if the bulb is good is under a failure - which is not desired. The only bulb that needs prove-out on these trucks is the brake warning light. Your truck has a temperature gauge, so no need to prove out a TEMP light as on some sedans. The OIL light (if equipped) doesn't need a prove-out circuit, since there is a brief moment that the engine turns over with no oil pressure, turning on the light. The ALT light (if equipped) stays on until the alternator begins to charge. However, there is no way for the brake light to come on unless there is a brake failure, so it needs a prove-out from the ignition switch. Thus the PURPLE/WHITE wire can go to either P1 or P2.

I'm a little sketchy on the remaining ones - one should be hot-in-ACCY (which is also hot-in-RUN), which powers the radio, wipers, etc. The back-up lights should not be part of this circuit as they should be hot-in-RUN. One should also be hot-in-RUN (only) which powers the heater, voltage regulator (which I think is what you meant by alternator), and throttle solenoid. These will be A1 or A2 - I'm just not sure which one is hot-in-RUN-ONLY and which is hot-in-ACCY.

I don't think that your list is completely correct because the throttle solenoid and the radio (d and f, respectively) are not powered from the same sources (one is hot-in-RUN and the other is hot-in-ACCY), yet you have them listed under the same color. Ford never used the same color to represent two different signals.

The I1 and I2 terminals are typically hot-in-START and hot-in-RUN (one of each) signals for the coil; RED/GREEN should go to the one that is hot-in-RUN. Typically the other one which is hot-in-START would go to the start-bypass circuit for the coil; however in some cases this is not used and instead the start-bypass circuit is powered from the 'I' terminal of the starter solenoid. However, again, I'm not sure which one I1 or I2 should be.

It's easy to confirm for yourself, however. Simply test continuity between the BATT terminals and any given terminal with a multimeter (set to beep function) for different positions of the key switch. That will help you map out the missing pieces.

I have the fat yellow wire coming in, have to verify which of the two batt positions it connects to. P1/P2 I can use for the brake warning then. On the radio/wipers/backup, that was from this diagram:

https://repairguide.autozone.com/zne...528004bba2.gif


what is a start-bypass? does that mean that one goes to the coil and still allows 12v during cranking, where-as it cuts power to everything else during cranking?


I also looked at this to start testing wires:
http://www.clubfte.com/users/mil1ion...nFaulttest.JPG



The other issue is that I'm connecting these wires to a universal wiring harness, along with custom gauges so most of the original wire colors don't help out so much. I did leave a section of wire on each switch as they had to mate with the universal harness. I can get the truck to run and shut off with a wire from the HEI directly to the battery, but the coil wire in the harness isn't getting power at all. The gauges / fan / radio / lights all work with the motor off. If the motor is off but the key is in the run position, everything else works fine. The minute the motor runs, the gauges no longer work. So I think I might have a position wrong on the back of the switch, one that should feed the coil wire and the other that should allow the power to keep going to the gauges when the engine is running.

ok, so I have a little update. The gauges work now except for the oil pressure. I think the switch might be bad, so I'll buy a new one to be sure. I still don't have power to the coil wire in the new harness, so I might try changing that to another spot on the ignition switch. Anyone else have any other ideas?

Starting at the top, I have my complete old harness out of my 77 and everything is still plugged in, so this is exactly how mine is:

ACC 2 = ORANGE/GREEN AND RED/GREEN BOTH WIRES

ACC1 = RED/BLUE

IGN1= BLACK/GREEN HEAVY WIRE

P2 = PURPLE/WHITE

BATT. = YELLOW HEAVY WIRE

This is on a 1977 2wd. Good luck.

Here is how I currently have it wired:

ACC2 w/ fat orange wire: going to new Ignition Switch ACC wire
ACC1 open
I1 with white wire: nothing connected, wire terminated
P1 open
1st Batt with fat yellow wire: going to new Ignition Switch Power
2nd Batt witt fat yellow wire: going to new Ignition Switch Power
P2 with purple w/ white tracer: going to new Ignition Switch Coil (this is wrong)
I2 with Red w/ Green tracer: going to new Ignition Switch Ignition
ST with fat black w/ Green tracer: going to new Ignition Switch Start

Based on the fact that everything cuts off when I crank (turns off radio, lights, etc), I figure I have one or two wires going to the wrong place. Plus, since I have no power at the coil, I am betting that the Ign Sw Coil wire I currently have going to the P2 location probably needs to be going to the I1 location.

Anybody concur?

i also have a 1979 f100.. i just pulled my ignition switch from the harness.. i'll repost what wire goto what prongs soon as i get it written down. I'll also try to take some pictures

ok so here is what i have;

Acc1 - Black w/ yellow (maybe w/white)
Acc2 - Orange
Bat - Yellow
Bat - Yellow
I1 - White
I2 - Red w/ yellow & orange (maybe red) w/green (or black)
P1 - Purple
P2 - open n/a
ST - Red w/ black & Red w/ white

If you want picture just message me with your e-mail and i'll send them to you. hope this helps

Not to look a gift horse down the mouth, but in the interest of maintaining accurate information on this forum, the actual colors are a little different than what you shared. The colors and positions on the back of the pigtail can be found in the bottom left corner of page 1 of the factory wiring diagram, shown here: http://fordification.net/tech/images...aster_1of9.jpg

FYI, this thread was started two years ago, so I doubt the OP is still waiting on the information.

Pictures
 

I have 79 f150 that some has jacked up the wiring and pulled se of the pins the resistor wire was burned up so put in a resistor block out out on the fender to do the same thing, the brown wire that comes of the resistor wire out to the starter solenoid is suppose to go in the I terminal but the truck wont run unless its cranking so I need to make sure all these wires are in the right spot. My email is jmitich429@gmail.com

Back to the top.
Where is the necessary Red w/blue wire? Obviously the circuit is working or your starter would not crank with the key in START.
Must be that Red w/black listed at the bottom as ST, but never noted a Red w/white wire sharing duties on the START circuit. Maybe for the Ignition Module?

The Red w/green wire would be the key here. It's the power to the coil in RUN/ON position and seems to be not working. The Brown wire is doing it's job, so the Red w/green is the culprit.
You can turn the key to ON and measure the voltage at the coil's positive side where the Red w/green is. Sounds like nothing is getting from the key to the ballast-resistor and then to the coil.

Good luck.,

Paul