Going it alone

I find it curious that no one has been down this road before. But, I think I have my answer.

I ended up calling the guy from the custom shop that worked on my wiring to get some answers. I haven't actually tested the end result yet, but this is what I was told, and what I found...

The mystery part in the picture above with the red and yellow wire is a circuit breaker. The custom shop apparently used this as a replacement for a factory part - he said it is "a more modern equivalent". It's not directly related to the blower motor.

Both from memory, and from looking at electrical diagrams, the custom shop guy relayed the following:

The rusty part in the second picture is the blower relay. I had pretty much guessed that from the reading I've done the past couple of days.

My understanding of the blower relay wiring, however, was incorrect. For some reason I thought the solo wire coming out of the relay was the fan motor wire. It's black, and it's tee'd into another black wire that goes back into the firewall. That didn't make any sense if it was for the blower motor - and it isn't.

There's a big purple wire that's part of the triple connector on the back of the fan relay that's supposed to go to the fan motor. That's what was fooling me and making it hard for me to figure out where my wire was hiding.

Another factor that contributed to the mystery, is that the custom shop had hidden the purple wire in the wire sheathing for the rest of the harness - it just came to a dead end alongside the other wires 3 feet away in the sheathing. I had to pull apart a lot of the sheathing, remove electrical tape, and generally have a grand ole time taking things apart, but I finally found the end of the purple wire and pulled it loose from the bundle.

After all that, I had to attach a female spade connector to the wire because, for some reason, the custom shop had taken it off. I added sheathing to the wire, and ran it to the fan.

Now, I'm hoping the fan works when I get the battery back in and hooked up.

Why all this silliness with the wiring? The custom shop said they usually just rip out all the old wiring and use a new harness. In my case, they were re-using original wiring to save money, so things were a little different from what they were used to.

 

You really need to get the shop manuals for a 74. When I nought my first 74, this was on the list of things to get. When I bought my 68, the manuals for it were the first things I bought. They are VERY helpful.

And inside the above manual is this:

As far as the place using a circuit breaker, that is fine BUT if there is an issue past the breaker it will open up and prevent power from going into a short but when it cools it will try and reconnect, see the short again and open and continue doing this over and over and over again and eventually the battery will go dead AND if things are not done right the wiring past it can be overly stressed. A fuse will blow and then it's telling you to figure out the issue and correct it.

Jim

 

I actually have that manual. However, I'm a novice at 12v systems and, quite honestly, the diagrams don't make much sense to me. For example, in the diagram above it isn't at all clear how to hook up the blower motor. It would appear from the picture that most probably a black wire should go to the blower motor (because it's the closest thing to the motor in the picture), and then there's this purple wire hanging out in the middle of nowhere (it's not close enough to the blower motor to seem like it should be connected to it). It's even possible to think that two wires should go to the motor, but there's only one connector on it. I haven't read it anywhere, but I'm assuming the motor is grounded to the chassis by its mounting screws since I can't see any other way for it to work.

Part of my full time job is to write technical and user manuals. I make sure things are clear and precise for someone with the least amount of knowledge to be able to figure things out. I guess diagrams like the one above are helpful to people who've been doing this for years, but I wouldn't put my name on something like that.

 

Lucky, Lucky YOU. I have an AC harness I took off of my 74 and I took some pictures of it.

First off, I took the one picture I took out of the shop manual and this might be easier to read. I took off the ground icon off of the connection they show going "TO JUNCTION BLOCK" which I think is something that should not have been there from the get go.

I then took pictures of the AC harness and then started laying out some of the connections and where they are on the diagram.

and the above partial numbering lays out with this diagram:

And here is the ground terminal end along with the bolt and star washer that I have to think went into a hole in the firewall close to the AC suitcase:

Off of the black ground wire attached to the firewall, the wire then goes into the loom and ends up at the push on terminal to the tab on the blower motor but somewhere in between taped inside the loom is a smaller black wire that branches off and goes to the AC relay (terminal labeled 150).

Jim

 

I don't know quite what to say, Jim. That's over, above, and beyond the call of duty. Thanks so much.

It's going to take me some time to digest this info, but at least the full meal is there to digest.

Part of the problem is that I'm coming behind someone that didn't quite finish their work. I compare what I see in the engine compartment with my (limited understanding of) what I see in the tech manual, and it's confusing. Per my last post, I found what I believe should be the black ground wire to the fan terminated and hidden in a wire loom that was headed back into the passenger compartment. That was totally confusing before I pulled things apart and found the wire didn't actually go anywhere.

Anyway, thanks again. I'll dig into your posting over the next few days and compare it to what I have.