Ignition switch help needed

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jjdeal79
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Ignition switch help needed

Postby jjdeal79 » Tue Jun 13, 2017 4:18 pm

Hello all. Yet again I have a question about wiring. My '72 F-100 (360, auto trans) had all the original wiring removed and replaced by an E-Z Wiring harness. I am trying to wire up an OEM switch, the style with the blades. I have spent much time with the wiring diagrams and hope that someone can dumb it down for me.

I would like to post two pictures, but the files are too big. At least that is what the error message says.

So i refer to the 1972 master wiring diagram posted on this site. I will list connections with Ford label and then the new wiring label. It starts and wipers/heater works how it is connected below and nothing has caught fire, yet.....

The top center blade connects to 21Y. I believe it goes to the battery and have connected it to my harness labeled IGN Switch Power.

Going counter clockwise, the top left connects to 98V -st cluster/ 297 BK-G. It's connected to IGN Switch Accessory. I do not know if this is correct as the original looks like it goes to the gauges.

Next is the bottom left and it connects to 32R-B, which looks like it goes to the starter relay. It is connected to IGN Switch Start.

Bottom middle original connects to 16PK, 932B - st cluster/ 16APK, 16R-G - RPO gauge cluster. It's connected to IGN Switch Coil. (?!)

Bottom left original is 977V. It looks like this one goes to the gauges too? I do not have anything connected to this with the new harness.

Top right. I have no idea. Looks like it isn't used.... I do not have anything connected to this one.

I need to connect the IGN Switch Ignition. When it was connected to the dinky switch that came with the harness, it was connected to the same location as the IGN Switch Coil.

As mentioned earlier, it does start under current condition. Any advise would be appreciated, and as always, thanks for your time.
-JJD-
1968 F100 4X4, manual everything, daily driver, climbs Alaska's Mountains, wife calls it "your big dumb truck".
Good thing I have the original shop manuals, so it always runs and proves her wrong when it snows!
1972 F100, work in progress "parts truck"
eventually will be the camping rig....don't tell the wife!

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MadMike
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Re: Ignition switch help needed

Postby MadMike » Thu Sep 28, 2017 2:47 pm

Make sure when looking at the schematic that you are looking at the appropriate wiring for your truck. If you haven't print out the pages and black out the part of the schematic that does not apply to your truck.
Trucks with factory gauges have slightly different wiring than those without. On the V.R. 'I' terminal is not used. Wires 655/654 are shunt wires for the ammeter and C 904 is used differently as well.
jjdeal79 wrote:So i refer to the 1972 master wiring diagram posted on this site...

The top center blade connects to 21Y. I believe it goes to the battery and have connected it to my harness labeled IGN Switch Power.


That appears correct, 21Y is the feed to the ignition switch.

jjdeal79 wrote:Going counter clockwise, the top left connects to 98V -st cluster/ 297 BK-G. It's connected to IGN Switch Accessory. I do not know if this is correct as the original looks like it goes to the gauges.

This is where having the original wiring harness, or at least the pigtail to the switch(which is available separately due to the resistor) comes in handy.
At connector 27(this would be the pigtail going to the switch) two wires come out. The dashed lines on the schematic indicate a splice, but are drawn out to better show where what components are attached to, rather than a cluster of wiring in a single point. This is not a wire that is stretched out but the actual splice point shown schematically.

98 V(15Ω resistor wire I'm assuming) that goes to S(plice) 6 which turns into 904 G-R.
297 B-G which goes to S(plice)7 which becomes 297A; 297B; 297C

297A BK-G Feeds the bus bar(feed) for fuses F5 & F1
297B BK-G Feeds C105 to radio and C31 to Wiper switch.
297C BK-G Feeds power to the gauges or idiot 'lites' depending on model.
Idiot lights have C-49 which plugs into the printed circuit board.
Non 84 Model trucks(check your serial number plate) have a 8-9Ω resistor wire part of 30 V which then goes to C10 on the CRV for the gauges.
84 model trucks do not have the resistor, but a harness or jumper for C50. Which then goes to the CRV for the gauges.
jjdeal79 wrote:Next is the bottom left and it connects to 32R-B, which looks like it goes to the starter relay. It is connected to IGN Switch Start.

32 R-B goes to a connector or harness between C-24, which I'm guessing is some kind of accessory or harness for differnet models, then 32 R-B becomes 32A R-B(part(wrapped in) of harness 14401 assy) which goes to the 'S'(tart) terminal of the Starter Motor Relay mounted on the inner fender.

jjdeal79 wrote:Bottom middle original connects to 16PK, 932B - st cluster/ 16APK, 16R-G - RPO gauge cluster. It's connected to IGN Switch Coil. (?!)

C-27 shows which way to follow. When you see ' } ' that indicates the optional routeing/wire harness.
If you have idiot 'Lites' your harness will be 16 PK & 932 B.
If you have 'Gauges' your harness will be 16A PK & 16 R-G.
Note that the differences is due to C 904 is used differently depending on if your original harness and truck was built with gauges or idiot lights, this is noted as before where the 'I' terminal on the V.R. is not used nor is the Stator terminal on the ALT.

jjdeal79 wrote:Bottom left original is 977V. It looks like this one goes to the gauges too? I do not have anything connected to this with the new harness.


977 V is from the Start terminal > C-25 > Brake warning switch harness > C-26 > Dual brake warning switch. Through the switch it becomes 977A V.
I'm assuming the Brake warning lamp lights up when starting to 'prove out' the light is functional when starting, but will go back out when the key is let go back to the ON/RUN position.

jjdeal79 wrote:Top right. I have no idea. Looks like it isn't used.... I do not have anything connected to this one.

Depending on if you have Lites or Gauges shows on the schematic how it is wired. Since you are only dealing with 977 V at the moment it only has to go down to the brake warning switch on the differential valve. It's 977A V that comes back off the switch and then connects to one side of the brake warning lamp mounted on the dash to the left of the key.
If you have lites the other side of the it connects to 640 R-Y which then goes to the splice of 932 B at C-11.
If you have gauges it connects to the end of 640 R-Y which then is spliced together with 904 G-R, 932 B, 16 R-G at S5.
Note there is the ' { ' but its horizontal and only with single wires so no break.

jjdeal79 wrote:I need to connect the IGN Switch Ignition. When it was connected to the dinky switch that came with the harness, it was connected to the same location as the IGN Switch Coil.


Coil is powered via two different circuits depending on Key position.
When turned to ON/RUN the coil is powered via 16 PK(lites) or 16A PK(gauges) that has an inline resistor of 1.3-1.4Ω.
When turned to START the coil is powered via 262 B with direct battery voltage from C3 or 'C' terminal on the starter relay.
-Michael


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