As always, thanks for your advice as I sort out my recently acquired 1974 F100 XLT, 2WD, 2100 2bbl, 3 speed manual. Was originally a 302, but now has a 1971 351W. (Note that it might be relevant to my question that the truck apparently had a six cylinder in between the original 302 and current 351W.)

Also, note that PO added an aftermarket distributor with a built in coil.

As shown in the picture (labeled with blue tape), there are quite a few extra electrical connectors under the hood that I’d like to identify. The truck runs fine with them disconnected, but I’d like to know what they are for as I try to get the truck back to the original look. Maybe some of these are left over from the 6 cylinder conversion? FWIW, I have the 5 volume shop manual, but can't find the answer there.

A – plugs #1 and #2 hanging from sheath on firewall.
B - plug #3 next to the windshield washer container.
C – wires #4 and #5 near heater/firewall (I’m guessing that one of these is for the under hood light … is this correct, and what is the other one for?)
D – plug #6 on intake manifold (I’m pretty sure this is for the original distributor)
E – extra wire #7 connected to battery side of solenoid (PO has spliced a wire here … is it correct for this to be connected to the solenoid, or is it supposed to get power from somewhere else?)

Thanks.

 

Uh oh, sorry if I overloaded with too many questions in one post. To narrow my question down ... does anyone know what connector/plugs (labeled with my blue tape) #1, #2 and #3 are for? These are the plugs shown hanging from the firewall, near the master cylinder, and the plug sitting on the windshield washer bottle. I think I've figured out the rest of the empty plugs. Thanks. Dan

 

I am not familiar with the 74 wiring but I would look at the factory electrical diagrams which can be found here...
1973-1979 Ford Truck Wiring Diagrams & Schematics - FORDification.net

Then identify connectors by location and wire colors and number of wires. Diagrams will help identify connectors wire colors and where they route.

You will learn alot. There are also several posts by others asking for help with identifying the same stuff that you can search the forums for.

 

4 & 5 look like they may have gone to an electric choke, but I don't know if that makes sense on a 1974. There's plenty of people on here who will know that though.

As for 1 & 2, I'd trace them back and see their origin.

You may want to take a few closer photos so we can clearly see what color wires are going to/from each plug. As orangeford mentioned, check out the wiring diagrams in the link he provided. They're worth their weight in gold.

 

Based on Orangeford’s tip, I now have the wiring diagram, and had it printed at Staples in readable size. And I’ve searched the forum and figured out most of my questionable wires.

But I’m still stumped on #1 and #3. (Not to complain, but the Color Key for the wiring diagram does not list BL or GR, but a bunch of the wires in the diagram have these labels. I was confused trying to figure out if these are supposed to be Blue or Black; and Gray or Green.)

I’ve figured out that #2 is (C-220) for the oil pressure gauge, water temp and coil. This makes sense since PO added mechanical gauges for these, and added an aftermarket distributor with built-in coil.

#s 4 and 5 are the Carb Vent Solenoid (C-486). I ended up connecting my electric choke to #5 since it was switched 12V.

I’m still stuck on #1. The wire colors seem to match C-320, but it is closer to the “engine compartment center of dash” than to the “Fender Apron” as indicated in wiring diagram. Does this look like C-320, and what is it for? As shown in the new photo, the colors appear to be Purple-Blue, Orange, Black and Gr (green or gray?).

I’m also stuck on #3. As shown in the new photo, the colors are Black/Blue dot, and Green. Also, note that the two wires for plug #3 join/pigtail with green and black wires on the ignition module plug. If I had to guess from the location, maybe this is for an idle stop solenoid? Any other ideas?

Thanks.

 

BL is blue
BK is black
GR is green
GY is grey

 

Going by connector shape only, #1 looks to me like C-323. The colors in your photograph don't line up exactly, but I know I've had plenty of color fading going on in my engine bay that it's possible.

#3 looks like it could be C-505 W/S Washer pump motor. The colors of the wires seem to line up with it too.

 

Thanks PapaBearYuma and sluijs01. I will look at the washer pump when I get home.

Regarding #1, I agree that it looks like C-323 for the ignition module. But you can see in the other pictures that the wires (C-323 and C-321) are hooked up to the module and sitting on the fender apron. Is there any reason that I would have two of C-323?

I’m wondering if #1 is C-320 … what is C-320 for? In the wiring diagram, I see C-320 is a similar looking 4 prong connector (the wire colors almost match mine) … but I can’t tell what it does from the wiring diagram.

 

Just realized I was looking at my 1979 schematics that doesn't have a C-320, and it looks like your ignition module for 1974 is unique from other years. I'm looking at your '74 schematics now.

It gets touched on here with someone else who was working on a 1974 F100, and NumberDummy points out that the ignition module is for 1974 years only. (https://www.ford-trucks.com/forums/1...lp-needed.html) So I'm guessing there's a chance that since your truck has an aftermarket dist/coil, that different harneses were needed and this was just left in place. It looks like on your schematic page that the C-320 is just one end of an extension cable with C-322 on the other end. I'd trace this cable out along your firewall and see where the other end goes. I'm guessing there's a chance you'll find another unterminated connector near your dist similar to or matching C-322.

 

Sluijs01, thanks for sticking with me on this thread. I appreciate your help. I think you are on to something noting that 1974 was the first year for the ignition module. If anyone is more familiar with 1974s, please chime in. I’m guessing that between ongoing changes with emission requirements and the new ignition system, maybe the wiring diagrams didn’t keep up? This would explain why some of the wire colors don’t exactly match.

I think I figured out connector #3. I’m pretty sure this is part of the TRS … I’ve seen a few acronyms, but I think it is Transmission Regulated Spark. See the attached pic … the plug shape matches the highlighted C-517 (or maybe it’s C-317, the diagram isn’t clear). I can’t actually find C-517 on the diagram, but it appears that it should be in the TRS section. Does this make sense? This might be a case where they were still trying to figure out the ignition and emission controls as they were making the diagram?

Regarding connector #1, as shown in the new pic, it looks to be part of the original harness. The wire goes through the plastic retainer (above the air cleaner) and then branches into the firewall (above the PCV) and branches back toward the solenoid. I think you are correct that this is probably unique to 1974. In the attached pic, it seems to me that C-320 isn’t fully shown in the wiring diagram. Again, is it possible that they were still trying to figure out the ignition and emission controls as they were making the diagram? I think it is more than just an extension cable as you suggested, but I’m stumped as to what it might be for.

 

Shoot, I didn't attach the pictures ... here they are.

 

The colors you indicated in one of the previous posts are all ignition related. The connector that looks like an ignition harness connector (common called "Duraspark connectors" for this very reason, even if they don't have anything to do with ignition) is the one left over from the swap to the HEI unit.
Since you don't have a Duraspark distributor or coil anymore, you have extra wires and at least one connector from that old part.

Paul

 

Since the PO introduced the HEI system, any and all ignition related wiring and boxes should be disconnected, taped off, etc. Things like the ICM and related wiring, the coil and related wiring.....why he/she left them there, connected, is anyone's guess.
There lies a problem.....if he just hooked up the HEI to the existing wiring the HEI's voltage will be wrong.

Here's why.....In stock form, these vehicles run with ~ 9 VDC to the coil, through a ballast resistor circuit. You have BATT voltage in START only, then the ballast resistor circuit comes into play in RUN.

The HEI unit requires BATT voltage (12 VDC) at all times. You only have two wires going into the HEI....one is Green ( for the TACH) the other is Brown (for START/RUN).
If switched 12 VDC isn't at the Brown wire going into the HEI she won't run optimally.

You can do this by finding/connecting switched 12 VDC (a three hole yeller pigtail under the left side dash) or bypassing the ballast resistor circuit at the ignition switch.....where START and RUN meet.

One way to check if you have BATT voltage going into the HEI - pull the BATT terminal from the HEI...key in RUN, Engine off....measure the voltage to ground. Hopefully the PO did the 12 VDC switch when installing the HEI.

 

Another way to get full voltage to the HEI is using the old Green w/red wire to trigger a relay under the hood.
It's more work of course, and you're adding a component that could eventually fail, but if you don't like to run new wires from under the dash, a relay is another option.

Paul

Paul

 

Thanks for the suggestions. I just checked and confirmed that HEI is getting full 12V. FWIW, it is connected to a white-red wire that comes from a Duraspark connector on the fender apron. Out of curiosity, in stock configuration, is the ballast resistor integral with the ignition module or is there a separate ceramic element like Chrysler?

So, the HEI only requires a single wire that is switched to the ignition run position (and start posittion)? That is good to know, and seems pretty simple.

I did add a tach wire to the terminal labeled "tach".

I was thinking that someday I might want to go back to the original Duraspark system as I restore the truck. But maybe that would be a mistake. I am still curious as to what the "Duraspark" connector hanging from the firewall is for, since I thought all of the Duraspark connectors were generally over on the fender apron area.

Thanks again to all who have replied.