Assistance with Restoring 73 Wiring Harness Options

[bbrock]

IIRC, there is only a positive wire to the heater light and the mounting screw through the brass eye side IS the ground connection. I'll take a look tomorrow if nobody confirms or denies. Don't get too excited about that light. It just comes on and stays on whenever the headlights are switched on.

On the intermittent wiper, I believe all cars have a terminal to connect the intermittent harness to, but not the harness unless the option is installed. If it isn't, the terminal is folded back onto the harness and wrapped in electrical tape.

[doug_b_928]

Thanks as always, Brent. I appreciate you checking into the heater light wiring for me. To go from what was always there, it will still be exciting to have that light present and working the way it originally did.

I had a closer look at the harness that, for some reason, I had labelled intermittent wiper (I probably looked at some documentation and erroneously concluded that must be what it was for). It doesn't look like that's what it was for and I don't recall if I disconnected it from anything but I'm thinking not. It is connected to the fuse panel at the front spade terminal of fuse 9. Then there is a fuse in line, then a branch with a short piece of wire with no connector on it, and then it connects to the rest of the harness pictured below at the spade terminal identified in the picture. The rest is as shown in the pic. Does anyone recognize what this harness would be for? It does look like an original, period correct harness...

[bbrock]

Just looked at my harness and confirmed only one wire going to the heater light. In the pic below, the wire to the heater light pigtails out of the connector for the center console illumination. I'm not sure if cars without center console have that connector, but I assume they do. The skinny terminal is connected to the male spade on the heater light, and the circuit is completed to ground through the mounting screw. And I hear you about getting even these "boring" little lights working. I'm the same way (IMG:style_emoticons/default/biggrin.gif)

Looking forward to hearing what the mystery harness is for. I don't have that. First thought is maybe the radio. Look on Jeff's site any of the radio harnesses match? I think those are on the classics section.

[doug_b_928]

Thanks, Brent. That also gives me a sense of how long to make that wire (mine was completely destroyed). According to the wiring diagram there is a ground wire that comes from another of those connectors for the centre console to ground at the screw. I guess it just goes between the bottom of the base and the chassis, rather then up inside the base (i.e., between the screw and the base).

Re the harness, I think that mess was in the area under the cowl...so that's probably why I thought it was for the intermittent wiper function...

[bbrock]

Thanks, Brent. That also gives me a sense of how long to make that wire (mine was completely destroyed). According to the wiring diagram there is a ground wire that comes from another of those connectors for the centre console to ground at the screw. I guess it just goes between the bottom of the base and the chassis, rather then up inside the base (i.e., between the screw and the base).

Re the harness, I think that mess was in the area under the cowl...so that's probably why I thought it was for the intermittent wiper function...

Just a warning, my harness was pretty damaged and I can't remember the original condition of that heater light wire. I know I replaced the spade so no guarantees the length on mine is correct. I'll look again at lunch to see if I'm overlooking a ground wire under that terminal, but it seems totally unnecessary since a metal screw is going to take that side of the circuit straight to ground once it is attached to the chassis.

I did a quick scan of harnesses on Jeff's site (the radio harnesses are in the wiring section, not classics) but didn't see anything that seemed to match what you have. Interesting mystery.

[bbrock]

Ah! I just looked at the schematic and it looks like the ground wire that goes to the heater light comes off of the center console harness rather than the main. Mine is in a box in the shed on "the back forty," so I can't look at it. But it looks like the ground wire from the main connects into the console harness and then pigtails off to the heater light. I'm not seeing it in the pic on Jeff's harness gallery but it could be hiding in there.

Did you look at the pic of the intermittent harness on his gallery to compare with your mystery harness? Your suspicion may have been correct.

[doug_b_928]

Exactly, so I figure I'll just make up a single ground wire with a female spade to connect to the appropriate ground at the main harness and with one of those little connectors with a hole for the screw at the other end of the wire (my car didn't have the center console gauges). Here's the image from Jeff's page. It's not the same schematic in terms of wire color as for our 73s, and on our schematic the black with blue is coming back from a double wire on the male spade in the insulator for the centre console.



I checked Jeff's page re the intermittent relay wiring and I don't think that's it. There should have been a brown with black lead for that harness and there's no relay socket on it.

[bbrock]

Exactly, so I figure I'll just make up a single ground wire with a female spade to connect to the appropriate ground at the main harness and with one of those little connectors with a hole for the screw at the other end of the wire (my car didn't have the center console gauges). Here's the image from Jeff's page. It's not the same schematic in terms of wire color as for our 73s, and on our schematic the black with blue is coming back from a double wire on the male spade in the insulator for the centre console.



I checked Jeff's page re the intermittent relay wiring and I don't think that's it. There should have been a brown with black lead for that harness and there's no relay socket on it.

No harm in adding that ground wire with ring connector, but I don't think it is necessary. The brown wire on the main harness side where the center console harness connects, runs back to the interior light (according to the diagram, and then to the chassis ground in the engine compartment. My hunch is the engineers decided to add that pigtail to ground on the console harness to provide a secondary, and closer ground as assurance the gauges would all have a good solid ground. I would further guess they were thinking mostly about the voltmeter although that goes a little counter to the crazy routing they chose to get power to the voltmeter. I'm confident the heater light will work fine with, or without that other ground, but it never hurts to add it.

[doug_b_928]

Brent, that was an awesome tip re digikey and thanks again for providing the part numbers. Wish I'd had those connectors earlier. They make things a lot easier.

So back at it today. I haven't figured out the mystery harness but hopefully that will be come clear as I get to that part of the main harness.

One thing I've noticed is that the wire that provides the power for the centre console gauges, and that pigtails power to the heater light, has melted to the other wires it is touching in the harness. It's wire 62 (black with blue striping). Here's the origin of the wire on the wiring diagram:



According to this, the wire comes from the 'Light Switch'. When I check for continuity I get it on one terminal on the light switch. But when I pull the wire on that terminal off, I don't get continuity on that wire. The really strange thing is I don't get continuity on any other connectors or wires on that switch, but I know there has to be. Anyway, given that wire 62 has melted in the past, what should I check to make sure that it won't happen again? As I get closer to the fuse panel with that wire should I add another fuse in line to prevent it from damaging the wire if it overheats again?

[doug_b_928]

Upon further investigation, things make a bit more sense. The wire for the heater light was pretty much nonexistent at the location where the light would be, the wire was melted up to its power source at the light switch. Someone had spliced in another wire to it about 7 inches back from the headlight switch (with the wrong colour which made it confusing). Here's that splice with butt connector (black with blue in and grey with red out).



Other wires to/from the headlight switch seem to have been affected by heat. There are others with butt connectors and mismatched wires and a few others had electrical tape wrapped around missing/melted insulation. Here's a view of that:



So, does it seem like the wire overheated at the heater light, that wire got really hot, and then shorted by the headlight switch? Or, would it be the reverse with something happening with that wire at the headlight switch and melting other wires around it?

Either way, If I replace everything with good, and hopefully correctly colored, patches of wire, should I be good to go?

[doug_b_928]

Today's question: I think I've figured out how I will run the 12G wire through to the steering rack area. I'm going to run a ground from the ground point screw by the frunk release handle to the fuel pump at the steering rack. I have a piece of salvaged ground wire with a ring connector but it appears to be 16G. Given that it's a far shorter run than the 12G + wire, am I ok to ground the fuel pump with the 16G wire? If not I can get a new ring connector and make a piece out of 12G.

[bbrock]

Today's question: I think I've figured out how I will run the 12G wire through to the steering rack area. I'm going to run a ground from the ground point screw by the frunk release handle to the fuel pump at the steering rack. I have a piece of salvaged ground wire with a ring connector but it appears to be 16G. Given that it's a far shorter run than the 12G + wire, am I ok to ground the fuel pump with the 16G wire? If not I can get a new ring connector and make a piece out of 12G.

(IMG:style_emoticons/default/popcorn[1].gif) I have the exact same question.

[JeffBowlsby]

Fellas, its a circuit. From the power wire, through the pump, to the ground. Its only as good as its weakest link. So a 16 ga ground wire in a 12 ga circuit would be the weak link and may not protect your pump or the + wire.

The stock 75-76 FP ground cable is a stout cable that goes to a screw to the chassis under the fuel tank.

[doug_b_928]

Makes sense, thanks Jeff!
PS. Does the mystery harness look at all familiar and anything I need to do to prevent the melted wire issue from the headlight switch?

[JeffBowlsby]

Don't know about the mystery harness. It may be a piece of some other harness, I am not familiar with it. Cannot say about the melted wires - that could have been caused by many things. Two loose power contacts rubbing together, abraided wires in contact, a shorted switch or other component. Just be thorough in your inspection.

[doug_b_928]

Perfect, thanks Jeff!

[doug_b_928]

My extremely limited knowledge of electronics continues...I'm trying to figure out the relays. A PO had disconnected two wires (going to fuses 2--white and 4--yellow) from the combination relay. I'm putting everything back to stock per the wiring diagram. Here's the diagram for the combination relay:



So the wires should connect to the relay as follows:

White = F
Red/white = 56
Yellow = 56a
Yellow/red = S

Here is the schematic on the side of the relay:



And here are the connectors on the relay:



The only code I can see that corresponds to the schematic is 56a, which is the spade in the middle.

So, the question is, how do I know which of the other terminals is which?

[doug_b_928]

Hoping someone will chime in about my previous post in terms of how to read the relay schematic so I know which pins are which. In the meantime, the power antenna and radio were wired by soldering in wires with in-line fuses as shown below:



The Radio is wired to Fuse 8 which includes the cigarette lighter.

The antenna is wired to Fuse 11 which includes the interior light.

Is this an appropriate way to power these devices? I'm guessing that Fuse 8 (cigarette lighter) gets power when the key is turned on. But I wonder if Fuse 11 has constant power because it includes the interior light? If so, should I power the antenna from fuse 8 as well or does the radio itself tell the antenna to raise and lower?

Basically, I guess the main question is what's the best way to wire the radio and antenna into the original fuse panel?

[doug_b_928]

I just searched some old pictures and it appears the modified wiring originally looked more like this?



So, it looks like fuse 12 (on the direct connection to battery side) was wired to an inline fuse that then went to the fuse 8. Not sure why they did this.

The antenna was powered from fuse 11

And probably the radio was powered from fuse 10...

So, to instead of figuring out what the PO had done, again, the best way to ask is, what is the correct/best way to wire in power for the antenna and radio?

[gothspeed]

Today's question: I think I've figured out how I will run the 12G wire through to the steering rack area. I'm going to run a ground from the ground point screw by the frunk release handle to the fuel pump at the steering rack. I have a piece of salvaged ground wire with a ring connector but it appears to be 16G. Given that it's a far shorter run than the 12G + wire, am I ok to ground the fuel pump with the 16G wire? If not I can get a new ring connector and make a piece out of 12G.

If you don't want to buy 12ga wire for this one short run. And if you don't mind appearance in that short distance, you can use three 16ga wires in parallel to the same connectors/lugs. You can heat shrink them together to make the wires look 'neater'. Otherwise just buy some 12ga wire to make it perfect (IMG:style_emoticons/default/smile.gif)

Here is a wire gauge calculator for length vs amps:

https://www.wirebarn.com/Wire-Calculator-_ep_41.html