I am trying to put a basket-case truck back together. I need to know what a group of wiring connectors coming from the firewall are for. I presume the D-shaped 3-pin one goes to the distributor seeing as how it fits and is in the right general area. I am not sure about the 4-pin or the little 2-and-1 three prong deal. I do not have a coil or coil pig-tail of any kind. Does the 4-pin go to a coil? Is one for an electric choke or something? Any help would be greatly appreciated.












Thanks,
jb

 

are these not all factory connectors?

 

Those are all factory. The 4-pin connector is the engine ignition harness (distributor pickup, ground, and coil negative terminal). The 3-pin connector (which looks like an electrical socket) is ignition module power. The other 3-pin connector is another engine harness. RED with a GREEN stripe is coil power and RED with a WHITE stripe is the temperature sending unit. Is the middle one WHITE or YELLOW? Does it have a stripe? The oil pressure sending unit would be a guess if it's WHITE with a RED stripe.

 

But how do these connectors go to multiple items each? The 3-pin plugs right into the only connector coming out of the distributor, so how can the 4-pin have anything to do with it? When you say the 3-pin is ignition control module power, does that mean from or to the module? Sorry to be a pain in the ***, but I am totally lost on these. Are they meant to plug into other whole-plug connectors or are they meant to have spade connectors stuck into them from separate wires coming from multiple components? Am I missing some harness/plug that connects the distributor and coil before plugging into these? Anybody have a pic of how these look all connected from the factory?

 

I'm not sure I understand your question. The 4-pin connector has four wires: GREEN, BLACK, PURPLE, and ORANGE. The BLACK, PURPLE, and ORANGE wires terminate to a 3-pin connector at the distributor. The GREEN wire continues on to the coil horseshoe connector. As such, there is a branch in the engine harness.

Power TO the module. The module does not actually provide power to anything (except to weakly bias the distributor pickup); its job is to sink the primary current.

Whole connectors.

You should have the two connectors (3-pin for distributor, horseshoe for coil) at the engine.

The 4-pin connector and the 3-pin connector that looks like an electrical socket plug directly into the ignition module, 1-to-1. Look up pictures of a Duraspark module and you'll see. The matching RED with GREEN stripe wire that would go to the other 3-pin connector would go to the coil horseshoe connector, opposite the GREEN wire coming from the 4-pin connector. The matching RED with WHITE stripe wire goes directly to the temperature sending unit using a 90-degree wire boot. You didn't say what color the middle wire is, but if it's for the oil pressure sending unit like I suspect, then it would connect in a similar fashion as the temperature sending unit.

Note that '75 is a one-year ignition module. The BLUE wires running to the ignition module power connector are unique to that year. Modules for '75 can be troublesome to find (many manufacturers claim their '76-up module is backwards compatible when it often isn't).

 

I have no horseshoe for the coil, but even if I did I am still failing to see how the GREEN wire from the 4 pin and the RED/GREEN wire from the 3-pin both get to the coil horseshoe beyond the connectors at which they terminate. Also my ignition module is already plugged-in on both connectors (no openings left) with wire bundles that run to the firewall that are separate from the ones shown in the pic. I have searched for diagrams and have found some illustrated ones that still don't answer my questions. Essentially, other than the corresponding 3-pin coming out of the distributor I have, there are no open connectors for the others to plug into.

 

Then part of your original setup is missing, or has been modified. Unless a '75 uses wire boots and not a horseshoe (someone would have to help me out there). It's the same idea and connectivity though. How is your coil connected?

I'll try again. In the factory harness, BLACK, ORANGE, PURPLE, and GREEN start at the 4-connector pigtail in your picture. All travel together to the engine. At some point along the harness, GREEN splits off and goes to one side of the coil horseshoe connector. BLACK, ORANGE, and PURPLE stay bundled together and run to the distributor as a 3-connector pigtail. The other side of the horseshoe connector makes its way separately to the matching RED with GREEN stripe wire of the flat 3-connector pigtail.

I don't understand what you're saying. The picture you posted showed two ignition module connectors, with nothing connected. Are you saying you plugged the ignition module back into these connectors? Or, are you saying you have a separate set of identical connectors, and those are connected to an ignition module? What exactly are you working with? Can you post pictures of the rest of your setup? Has the wiring for this truck been modified in some way?

Here's an example of a Duraspark harness (slightly different than yours, as it's a later year) that shows how the 4-connector pigtail branches off to a 3-connector pigtail and part of the coil horseshoe connector. The top middle connector is the same 4-connector pigtail shown in your picture. The 3-connector pigtail in the bottom left goes to the distributor. Don't worry about the 2-connector pigtail in the top right. The coil horseshoe connector is shown in the bottom right.

 

I currently have no coil. I was waiting to get one until I figured out the wires that ran to it. My ignition module is still mounted on the driver's side inner fender and has two separate bundles of wire already plugged into its connectors. The wires shown in my pic come off the firewall right at the center behind the engine. I am not sure that any of them could even reach the module if I tried to connect them to it. They reach the front of the engine where the distributor and coil would be. There are no loose wires I have seen (yet) that would go to the coil or a coil connector. I am at work right now for a few more hours. I'd have to wait until this afternoon to post a pic of my module. thanks for staying with me this far. What does the 1-year only blue wire do?

 

As usual, FMC400 has provided some very helpful advice and photos, and he likely knows more about than I do. But, something about your setup doesn't look right. In particular, the 4-wire harness coming out of your ignition bundle at the firewall. That has no where to go. If memory serves, on the 1975 system you should have a 3-wire harness (red, white and blue), that plugs into a matching harness coming off your ignition module. Then you should have a 4-wire harness (black, purple, orange and green) that plugs into a matching harness coming off your distributor. On the distributer side of that plug, the black, purple and orange continue to your distributor and a green wire goes to the tach side of your coil. In other words, if the 4-wire harness coming off your firewall is the purple, black, orange and green harness, I can see why you are confused, because I don't think that's where it belongs.

 

The only thing is, my distributor only has a 3 wire/3-pin harness coming off of it. No provision to run the Green wire to the coil. 400's pic makes sense but it is different from the wires I have found. I will send more pics including the module later today. I have been considering converting the system to use 12 volts running from the ignition switch to a 4 pin GM ignition module. Anybody familiar with this set-up? Would I risk losing anything crucial by bypassing the OEM module? Thanks again.

 

Your distributor SHOULD only have three wires coming off it. These are purple, black and orange and mate with the purple black and orange on the harness coming off your module. That harness from your module will also have a green wire. It goes to your distributor. I'm not sure if it will be visible but I copied a basic duraspark set-up below. It's different from the 1975 setup, but the routing of the 4 wires coming off the module is the same. Note that three of the wires (orange, purple and black) run to the dist by way off the two plugs. The fourth wire, the green, seperates from the others at the plug and runs to the tach side of the coil.

 

I will post some pictures later today as I have a 75 with 390 sitting here in the drive. Camera is in another truck. On this truck the 3 wire plug has nothing plugged in it. They are using the flat plug and the 4 wire round. There is a harness that runs along the valve cover goes up to the coil and dist. I would also guess that the water temp, oil pressure sender wires are in that harness too. I have to post using photo bucket but will try and get that done before tonight for you. This coil is using the familiar Ford horse shoe connector.

 

Okay. Here is a pic of the wires coming out of my ign. module. They cleanly join the other wires running through the intact rubber firewall grommet right behind the headlight switch area of the dash.




Here are the loose connectors/wires coming cleanly from the group of wires that come through the intact rubber firewall grommet slightly to the passenger side of the bellhousing area.



I am assuming that because the grommets are not all tore up and that there are no big lump of spliced connections anywhere that this is a factory wiring set-up.

 

Okay, things make a lot more sense now. Thank you for clarifying with more pictures. The ignition module and its connections shown in your first picture are correct.

Based on this new information, the second set of wires you're showing shouldn't be there. There's absolutely no reason for them to be here and it is most certainly not factory despite the initial appearance. Someone somehow has put together some sort of Frankenstein harness. As Old Coyote describes, that set of connectors shouldn't have been at that location in the firewall in the first place (something I missed the first time around).

Here's how I know. In your second picture, the wire colors leaving the firewall harness are not the same colors that end up running to the connectors in question. That means there is some splicing under all that tape. This is some sort of custom harness that someone built for a specific purpose and re-used factory-style connectors. You're looking at something a previous owner cooked up and it's anybody's guess as to what it's for.

This isn't the weirdest thread I've come across but it's up there!

 

I'm still anxious to see what IHC1470 has to show me as far as his pic goes but looks like I may be leaning towards the GM HEI module conversion. Anybody have any opinions on that? Here is a diagram of how it works apparently. Looks pretty simple to me.




Prob be a good way to forget about the one-year-only Ford module for the blue wire.