Studying the schematic

[Ellie Niner]

Shunted ammeters, like what the factory installed in 1973-75 trucks, aren't a fire hazard... though I suppose you could get a few pops and a little smoke out of one if you bypassed the factory wiring and fuses. The problem I had with my '75 was that the thing never read more than about 1/8 scale either direction... I spent more time than I care to admit screwing with the thing, and finally got it to read correctly. One thing it did better than a voltmeter is telling me when my battery was fully charged when driving home from parties out in the countryside... those ones where you have the stereo cranked up for 4 hours without running the engine. Usually was about 30 or 40 minutes into an hour drive back home before the needle would come back to center.

Full current ammeters could be a fire hazard if you have wiring that's too gimpy or loose connections somewhere... the worst I've gotten (so far) was a big arc when I was screwing with the instrument cluster in a 1978 Dodge truck without disconnecting the battery. One of the lugs on the ammeter grounded against something.

I'm guessing that part of the reason ammeters went away is that they wouldn't serve much purpose on a modern vehicle. They only show if the battery is being charged or discharged, and all modern rigs have monster alternators that can keep up with everything once the engine is running... so the thing would only show a charge for a few seconds after starting the engine, then stay in the middle the rest of the time. It would take a hunk of donkey d¡ck sized wire to feed a ~150 amp full current ammeter, and then the average driver wouldn't have a clue what it meant anyway... Quite a few modern vehicles with full instrumentation contain "gauges" that are just bullsh¡t. Ford has had fake oil pressure gauges and voltmeters in a lot of their vehicles since about 1987 or 88, and I know that the GMT360's only have an open/closed oil pressure switch on the engine. Even the ECU only gets an idiot light style signal for oil pressure, but it just tells the instrument cluster to read somewhere around 40 psi.

 

[Raider L]

@SquareRoot,

And last night after I wrote about that junction block I went on line to try to find a schematic on my year truck with A/C. I found one on another forum. I did go to our library to find one first, but it wasn't there. After looking at the schematic I found, and the way the wires are connected to that junction block I agree 107% with you that that's all that is, is a place for wires to be connected. It is not not a "fusible link". In looking more closely at that on my schematic where it talks about a fusible link at the junction block there, it's referring to the way a actual fusible link is, like what is in that pic you showed. Those fusible links are down at the starter. I guess that's the way my truck was built. I never moved them from down at the starter when I did all that rerouting of the wiring to up there on that block I made.

When I looked at that schematic for a '73 truck with Air, there they were, all the same colors and locations. I was looking at the colors of wires on the plug going to the fan speed switch behind the dash, they weren't the same color as the wire color on my schematic. That's what threw me off for so long. I thought it was wired wrong, which isn't unusual for this truck especially after finding that horrible splice of the Alt. wire up there on the junction block a couple of weeks ago when I was routing my Amp gauge wires. But, no, the colors of the wires are exactly what the schematic I found, are. And that big orange wire up there on the junction block is where it's supposed to be because it's additional power for the fan when you turn the A/C on, instead of the A/C switch getting all it's power from the little wires from the fan speed switch. It gets additional power feed from that fan control wire being connected right there with the stater power wiring.

So, I want to thank everyone for your help and direction on this project. You know how confusing schematics can be. I had plenty of experience with figuring them out when I worked on big passenger planes. Imagine those wiring diagrams.
That's why when I got my factory maint. manual from the local Chevy dealer, and came across that schematic in the back the first thing I did was take it to a printing place and had them blow it up three or four times. I took all the pages that they printed out and layed it out on the floor and then lined all the corresponding lines up and taped all the pages together. It was now big enough where it is no trouble finding out where all those wires go.

 

[Raider L]

@Ellie Niner,

WOW! Yeah, I wanted an Amp gauge in the truck ever since I bought this truck and saw that it had both, volts and amp. from the factory. Although I couldn't figure out what had happened to the Amp gauge, it never worked. And like a dummy I hooked up my Autometer Amp gauge to the factory wiring when I rebuilt the truck. I figured, "Well, it's already in the truck, and it appears to be wired like Autometer says to hook theirs up, so I'll just use those wires." Of course totally disregarding the fact the factory gauge didn't work, I guess I figured a new gauge would work because something had broke the factory gauge. To this day, even after I have wired up the new Amp gauge, have I found out why the factory gauge didn't work. There was no sign of damage, the gauge was plugged in tightly into the printed circuit, like the gauges are in stock configuration, so I guess something inside of it just failed. The factory volt gauge worked fine. So it's a mystery.

And yes, I agree that gauges in vehicles these days are a waste, unless it's a Subaru WRX racing street car that really needs real gauges, the rest is just dress-up. "Oooo, I have gauges!" And especially with guys. They want to see gauges because that means they've bought a race car. It feeds their ego. They get a twitch in their balls when they can go fast and look at some meter on the dash that tells them they're going fast. The car makers laugh themselves sick all the way to the bank. That's why I went against advice to buy a new truck when I had the money to do so. No, I want to build my own truck so I can put everything into I want. I wanted a hopped up truck so if I wanted to go fast, it really would go fast and not because it looked fast, and based on the salesman's ability to convince me I was buying a fast truck.

 

[Bextreme04]

I'm about 107% positive that junction block is just a junction block. Technically, it is a "bussbar". The metal strip is not any type of fusible link. The #10 wires on each side of it would melt way before that strip of metal would. I have 200 amp fuses in my truck protecting my amplifiers that are a tiny fraction the size of that metal strip. A fusible link will always be insulated to prevent fires is it burns. My guess is fusible links may connect to that junction block. My wiring diagram isn't exactly user friendly. It's accurate but hard to decipher details.

That pic I posted was not mine, it was off the net. My truck is way beyond stock and 99% of my wiring has been replaced and modernized. But, I know every wire, connector and device on it and have a logbook of each circuit.

This is correct. That is a junction block and is in NO WAY a fusible link. @Raider L you should have fusible links at the starter connection AND at the junction block per the schematic. My truck is an AC truck and has fusible links at both ends... still the original crimp and same wire color as listed on the schematics. I think someone cut your fusible link out at some point and never replaced it.

 

[Raider L]

Okay, I just got through switching the starter power wire over to the small screw on the junction block along with returning the fan motor wire with the 20 amp. fuse on it to that screw as well. It's such a little change but as far as complying with the schematic layout, it's how I believe it should look. Sorry, I'm picky that way. Pic follows.

 

[Raider L]

@Bextreme04,

I have two down there on the starter. But my schematic only shows one should be in the starter wiring. Like I said if it was on the truck when I cut all that extra wire out of the factory starter wiring, I left everything just like it was and just cut it in half and put it all up on that block I made. It's all there, as far as I know. That fusible link you mentioned might very well be the second fusible link down there on the starter, along with the other one down there, because the schematic only shows one in the starter circuit. Only the #16 orange wire is going into the second fusible link, there. The dark colored wire behind it is the #10 purple wire that goes to the starter switch on the column. It only looks like it's in that second link, it's not. It's just behind it.

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The above pic shows the two fusible links on the starter. One wire is the #10 red power wire. The other is one of those tan wires. That dark wire behind the top fusible link is not on the link, it's the #12 purple wire. It goes to the ignition switch up on the column.
In the pic above see that straight piece of metal, you can see part of the solenoid there? That's a Moroso starter heat shield. That brown round looking tube in front of it at the bottom of the pic, that's a header tube! The photo is taken looking up. It's not that close but all the protection I can get there, the better.

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This above pic is a bit better lit, but the colors aren't that bright due to engine heat and wear, I guess. I need to clean them and they'd be better identifiable. The large red wire in the back ground is the battery cable.

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At the solenoid you see the battery cable, and to the right of that are the wires from the fusible links. I could crawl under better so all the wiring connections would be clearer. This is the best I could do with the truck just sitting. I'd have to jack it up some to get a better picture.
You can see the Moroso heat shield on edge in this pic. It's two Alum. sheets with some kind of heat proof material in between.

 

[Bextreme04]

@Bextreme04,

I have two down there on the starter. But my schematic only shows one should be in the starter wiring. Like I said, if it was on the truck when I cut all that extra wire out of the factory stater wiring, I left everything just like it was and just cut it in half and put it all up on that block I made. It's all there, as far as I know. That second fusible link you mention might very well be the second fusible link down there on the starter along with the other one down there, because the schematic only shows one on the stater circuit.

I'm not sure what schematic you are looking at... but this one matches what I have seen on trucks in person. The part circled in red is the starter wires and clearly shows that one lug(that goes to the same spot your battery wire goes to) has two wires connected to the same connector, both of which have their own fusible links.

The wiring on each of the two terminal blocks then has a single wire(with fusible link) that then splices to three smaller wires. I haven't bother to track the wiring to other sheets to see what those go to, but you should clearly have more fusible links in there. Also, that run to the blower motor would not have had a 20 amp fuse on it originally. The circuit is protected by the fusible link in the original wiring.

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[Raider L]

@Bextreme04,

That's exactly the same schematic I'm using! That's the factory schematic, but the wiring changes for trucks with A/C. That's what messed me up. I kept looking for this wiring that had different colors than what I was looking at in my truck. Here's the schematic I found on line. But, since I don't have any ink in my printer I had to hand draw it. But it's accurate. If you'll look on it near the bottom it shows the junction block and the #10 orange wire is not on it. There's a #10 red wire? That #10 orange wire is shown going inside and goes to the fan speed switch. But the colors are correct for what I see in my truck now. Some of this wire is on your and mine schematic and some isn't. As far as fusible links in the start circuit, I don't know what to say. The ones down on the starter you see in the above pics are the only ones that have ever been on the truck. It's never caused a problem so....? And that orange wire with the 20 amp fuse on it? It was like that when the A/C was in the truck, so I left it like it was. I guess it was put there at the factory because it was part of the A/C. Why? I don't know anything about A/C circuitry. But today I did switch that #10 red starter wire to the side of the junction block this schematic shows it. So it's on there now. But so is the #10 orange wire!

Update Friday night--I've looked at several dozen diagrams and this one is the only one for my year truck. It's only difference is the #10 red wire from the blower relay it shows going to the junction block is not in my truck, anywhere! My truck's wire from the relay that is on the junction block is a #10 orange. This schematic shows the #10 orange wire goes to the fan speed switch. Mine terminates at the junction block, but is also getting power from the #10 red battery/starter wire at the junction block. Otherwise this schematic is like my truck. If yours is different, that doesn't mean it's wrong, or somebody messed with it. So long as there are no problems and everything works like it should, then it's fine.

If anyone wants to make a copy of this A/C schematic please feel free to do so.

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[Raider L]

I got this schematic from "73-87 Chevy Trucks.com Parts, Restoration, Community".

One thing about how I left the truck from when it had air, is, when I put the slider on the heater/A/C control where you can open the door more on the heater core, and make it hotter in the truck without turning on the heater, I can put the slider on "A/C" and the fan will go straight to HIGH!. Now is that because of that #10 orange wire? Could be. It may be because of the A/C wiring I left behind, but it goes straight to high. But if I want to put more heat in the cab without turning the slider to "Heat", I can't get the fan on high. I can get "low" and the "med." setting but no high. Now that I'm thinking about it I never tried to slide the heater core door open some more to get more heat in the cab, then with the other slider put it on "A/C" and the fan would go to "high". I guess I live in Louisiana and it hadn't never got that cold. If it did I'd probably just put the slider on "Heat" and it would get a lot hotter even without opening the vent door more.

Now, guys who don't have A/C, theirs don't have the "A/C" on their function selector, "heat, A/C, vent", slider. I've never seen that so I don't really know what's on a non-A/C truck. Somebody got one? Take a pic of your function selector slider down there so we can see the difference.

 

[Raider L]

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The above pic is of the #10 purple wire down on the starter solenoid. It goes from there into the harness and into the cab and goes to the ignition switch.

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The above pic is of the #10 red wire on the solenoid. From here it goes up to the junction block.

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The above pic is of the #16 orange wire on the solenoid with fusible link. It goes from here to the ignition switch.

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The above pic is of, I think it could be one of the factory amp meter wires that went on the solenoid. I need to trace that wire by putting a light on it and if it is one of the old amp meter wires I'll cut it out because it's not needed anymore.

 

[Raider L]

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The above pic is of the other end of the #10 red wire that goes to the solenoid.

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The above pic is of where the end of that wire goes to the junction block.

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The above pic is the Alternator wire.

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The above pic is just showing the #10 red wire that goes to the starter is just running for a short distance in conduit to clean up the look, that's all.

 

[Raider L]

@Ellie Niner,

This should interest you. When I was putting in the Autometer ignition system stuff, the tech guy said to put this in line with the one of the starter wires, and he said which one, I don't remember what he called it. He said it would keep stray over voltage from the starter coming back up after starting that could harm the electrical system. He said it acts as a valve in that one end of the wire you get continuity and the other end of the wire you'd get no current indication. He said to make sure you turn it the right way so juice goes down to the starter, but none can come back up. What's that thing called? Here's a pic with the number on it because he told me which one to get that has ( ???) value. I don't remember, you tell me.

 

[Raider L]

@Ellie Niner Here's what I was referring to in the above post.

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This is a closeup of the number on it. I'm sure I have the info on this little thing, but it's in my rebuild notes and stuff and I'd have to do some digging to find it. It's not a "shunt" I don't think. I don't recall names of electrical things like this. It has a "value".

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In the above pic you can see it near where I'm pointing. In the pic I'm pointing to another wire but you can see it in one of the wires going down to the starter.

 

[Raider L]

I don't know about ya'll, but I'm sick of seeing all this wiring. I'm ready for some different wires to look at!

 

[Raider L]

@SquareRoot,

Looking at the schematic you are correct in that the #10 red wire on the solenoid on mine does have a fusible link on it. On the schematic the other fusible link shown is on the Alt. wire, and it goes to the junction block which mine does, but doesn't have the fusible link on it and that's the one you're talking about. I can get a fusible link off line and put it in line with that Alt wire on the junction block I re-did. That's cool, and then it will match the schematic. There's two drawings of the junction block and it's confusing as to which is mine and which is another kind of truck. Notice the schematic has stuff on there for 6 cyl. engines, and Blazer stuff to, but just lights for it and a crew cab.

I do have those #12 red (2D)and as it shows there's supposed to be a #12 white wire (2E) both coming from the Alt. MY white wire coming off the Alt. is not that big. It's more like a #14 wire. But both of those wires are spliced together just before they get to the firewall just like it shows in the schematic. #12 2D goes to the junction block, and #12 2E goes to the ignition switch on the column. Which it does.

So, my wiring is okay now except for that fusible link in the Alt. wire at the junction block, which I will get and put in. And it says it's supposed to be a #16 wire in the link. Whatever.