Studying the schematic

[Turbo4whl]

Yes, triangle or arrow. The different types:

Schematic Symbol	Symbol Identification	Description of Symbol
You must be registered for see images attach	Semiconductor Diode	Semiconductor pn-junction diode which passes current when forward-biased, and blocks current flow when reverse-biased. Commonly used in small-signal, rectification or high current applications
You must be registered for see images attach	Zener Diode	Zener diode used in its reverse voltage breakdown region for voltage limiting, transient suppression and regulation applications. Available in a range of reverse breakdown voltage values
You must be registered for see images attach	Schottky Diode	Schottky diode consisting of an n-type semiconductor and metal electrode junction producing a very low forward voltage drop and power dissipation and faster switching speed compared to a pn-junction diode
You must be registered for see images attach	Light Emitting Diode (LED)	A semiconductor diode which emits a range of visible and non-visible coloured light from its pn-junction depending on the materials and doping used when forward biased
You must be registered for see images attach	Photodiode	A semiconductor photosensor which allows current to flow through itself in the reverse direction when exposed to incident light energy

 

[AuroraGirl]

I'll take you further down the rabbit hole. When you have any kind of electrical coil, it makes a magnetic field. That magnetic field does the work to pull a pintle or close a switch.

When the coil power is shut off, the magnetic field collapses in on it's self. When this happens the coil generates a higher current voltage. Being a higher voltage it now flows backwards to the switch that just turned it off. The diode protects the switch or circuit.

If you look at the wiring diagram printed on a quality Bosch relay, along with the connections in the diagram there will be a diode.

Is there any value to GM Oem bosch relays. And do you know if there is anyway to make use of the ones which have a "skirt" that passes beyond the bottom , meant to shield whatever it connected to I assume.

 

[Turbo4whl]

Is there any value to GM Oem bosch relays. And do you know if there is anyway to make use of the ones which have a "skirt" that passes beyond the bottom , meant to shield whatever it connected to I assume.

You would find the Bosch type relays with the skirt in conditions where there is moisture or possible oil contamination. The plug for that type relay is longer and has a seal like a weather pack plug. You could use that relay on a fuse panel by just cutting the skirt off. Since the skirt is usually larger than the base of a relay without the skirt, it may not work on a panel where the standard relays are placed close together.

As far as the quality of a relay, the cheap ones are lighter in weight then a quality brand name like Bosch or Delco Remy. So less windings, thinner conductors and may not even have the built in diode. All you need to do is open up the relay (bust the cover off) and you can see the difference.

 

[AuroraGirl]

You would find the Bosch type relays with the skirt in conditions where there is moisture or possible oil contamination. The plug for that type relay is longer and has a seal like a weather pack plug. You could use that relay on a fuse panel by just cutting the skirt off. Since the skirt is usually larger than the base of a relay without the skirt, it may not work on a panel where the standard relays are placed close together.

As far as the quality of a relay, the cheap ones are lighter in weight then a quality brand name like Bosch or Delco Remy. So less windings, thinner conductors and may not even have the built in diode. All you need to do is open up the relay (bust the cover off) and you can see the difference.

So I looked earlier, I have bosch and "hella" relays. 90% sure they were late 80s, early 90s OEM gm ones. Never heard of hella relays.

 

[davetyp]

@SquareRoot,

What the schematic is calling the "fusible link" is up on the junction block there is a thin plate thing that connects between the 1/4" screw and the #10 little screw. ... To my understanding that thin "plate" is supposed to melt if there is an overload.

That's just a bus bar. It would take a LOT of current to actually melt that plate through, probably more current than the battery could even supply. A fusible link is usually (always?) a short section of much smaller guage wire designed to burn through if the current gets too high. I've always wondered why GM didn't use 50 or 75 amp fuses instead, but I suppose they had their reasons. Fusible links were probably cheaper than high current fuses. Certainly cheaper than circuit breakers.

 

[Bextreme04]

That's just a bus bar. It would take a LOT of current to actually melt that plate through, probably more current than the battery could even supply. A fusible link is usually (always?) a short section of much smaller guage wire designed to burn through if the current gets too high. I've always wondered why GM didn't use 50 or 75 amp fuses instead, but I suppose they had their reasons. Fusible links were probably cheaper than high current fuses. Certainly cheaper than circuit breakers.

It had more to do with the poor electrical design of the older systems. The way these older truck electrical systems were designed had LOTS of EMI in the system and you could get significant surges in voltage as things turn on/off. When they went to EFI and digital sensors, they had to redesign the electrical systems to get rid of a lot of that interference so that the ECU could read the correct parameters without getting fried. This is why the EFI vehicles go to relays and fuses for almost everything. The factory GM relays will have a diode(or often a resistor) in the activation circuit to reduce the EMF spikes in the system. The older carbureted engines don't really care about voltage spikes or EMF, so they just used the cheapest and easiest to produce system possible. The reason they used a fusible link is because it will allow a large voltage spike over a short period of time without melting the link. A similar sized fuse will blow instantaneously when it gets that spike.

 

[AuroraGirl]

oops

 

[Raider L]

@Turbo4whl, davetyp, Bextreme04,

Boy, I'm glad ya'll covered the topic of the fusible link verses a fused connection because like @davetyp said about the fuses, that's exactly what I was going to do. And instead of a "fusible link", i.e, a smaller wire on the Alt wire connection like the factory had it, I was going to put a fuse on the Alt. wire! I didn't know how big it was supposed to be, but I would have found out and put the dang thing in there. Now I see, like @Bextreme04 said, the smaller wire was designed to take more of a surge and not melt and a fuse would blow as soon as it took the spike. So I'll just splice the smaller wire, in this case it will be a #16 wire. But here's a little problem with that. The factory put a #12 wire coming off the Alt.. Then up near the junction block there is a splice with another #12 wire that goes inside the cab to the ignition switch. What I did, for my Autometer Amp gauge connection was spliced the #12 Alt. wire with a #10 wire as one of the Amp gauge wires going to the junction block like the Autometer instructions say to do. Now back to the fusible link question. Do I go down to the #14 wire for the #10 wire's fusible link going to the junction block, which is the correct wire size for the #10 size wire, or consider the size of the #12 factory wire coming from the Alt. originally, which would make the fusible link wire size for it a #16 wire? Reason being if there is a spike which wire will go first the #12 wire coming off the Alt., i.e. it's #16 fusible link wire, the #10's fusible link wire i.e. #14 wire?

This question comes from the fact that I had to put #10 wires on the Amp gauge so the Autometer instructions would be followed for the correct size wire for the current the amp gauge would be handling. But when I found out by untaping the factory splice of the alt. wire is two #12 wires and not #10 wires coming from the Alt., I went ahead and put one of the Amp gauge wires on the alt. wire for the first leg of the Amp gauge wiring. I kept looking at that #12 wire coming from the Alternator thinking all along, "Is this right? The Autometer instructions say use a #10 wire for the connection and here I'm putting a #10 wire on a #12 wire? That doesn't seem right because now the fusible link becomes the dang Alt. wire!"

Or, again, am I over thinking the matter? It will be the smaller wire that will take the spike and it'll probably be okay either way?

 

[Raider L]

Now, what I could do is replace the #12 Alt. wire with a #10 wire for the Alt. power wire at the Alt. That way all I would need is a #14 wire for the fusible link at the junction block and it would all be the correct size. Concidering the Alt factory splice there, the #12 that goes into the cab to the ignition switch would be okay anyway. Otherwise the factory just should have used #10 wire throughout the whole system!

The truck would have gained about ten pounds in weight due to all the copper wire on it! Lol.

 

[Bextreme04]

@Turbo4whl, davetyp, Bextreme04,

Boy, I'm glad ya'll covered the topic of the fusible link verses a fused connection because like @davetyp said about the fuses, that's exactly what I was going to do. And instead of a "fusible link", i.e, a smaller wire on the Alt wire connection like the factory had it, I was going to put a fuse on the Alt. wire! I didn't know how big it was supposed to be, but I would have found out and put the dang thing in there. Now I see, like @Bextreme04 said, the smaller wire was designed to take more of a surge and not melt and a fuse would blow as soon as it took the spike. So I'll just splice the smaller wire, in this case it will be a #16 wire. But here's a little problem with that. The factory put a #12 wire coming off the Alt.. Then up near the junction block there is a splice with another #12 wire that goes inside the cab to the ignition switch. What I did, for my Autometer Amp gauge connection was spliced the #12 Alt. wire with a #10 wire as one of the Amp gauge wires going to the junction block like the Autometer instructions say to do. Now back to the fusible link question. Do I go down to the #14 wire for the #10 wire going to the junction block, which is the correct wire size for that size wire, or consider the size of the #12 factory wire coming from the Alt. originally, which would make the fusible link wire size a #16 wire? Reason being if there is a spike which wire will go first the #12 wire coming off the Alt., i.e. it's #16 fusible link wire, the #10's fusible link wire i.e. #14 wire?

This question comes from the fact that I had to put #10 wires on the Amp gauge so following the Autometer instructions would be followed for the correct size wire for the current the amp gauge would be handling. But when I found out by untaping the factory splice of the alt. wire is two #12 wires and not #10 wires coming from the Alt., I went ahead and put one of the Amp gauge wires on the alt. wire for the first leg of the Amp gauge wiring. I kept looking at that #12 wire coming from the Alternator thinking all along, "Is this right? The Autometer instructions say use a #10 wire for the connection and here I'm putting a #10 wire on a #12 wire? That doesn't seem right because now the fusible link becomes the dang Alt. wire!"

Or, again, am I over thinking the matter? It will be the smaller wire that will take the spike and it'll probably okay either way?

You are overthinking this. The larger wire won't hurt anything. Larger wire will have less resistance to power flowing through it and will heat less and have less voltage drop over the run. The fusible link will be the proper size and length to protect the wire run that it is intended to protect. The larger wire gauge before or after that fusible link will make no difference in its operation at all. At worst the larger gauge wire will just be unnecessary, but will not hurt anything. You size wire for the maximum amperage you expect it to handle and the length of the run. Fusible links are sized to protect the wire run they are connected to. So you could maybe size up the fusible link on some of these wires you replaced with larger ones. General rule of thumb I've heard is two standard sizes smaller than the wire it's protecting. So since you upgraded some wiring to 10 AWG from 12AWG, you would need a 14AWG fusible link for that wire protection instead of a 16AWG. If the alternator doesn't actually produce enough amperage to NEED a 10AWG wire, then you would NEVER blow a 14AWG fusible link unless it was a dead short. Unless you have beefed up the alternator and are running lots of extra electronic components, I would suggest you stick to the factory fusible link size.

 

[Raider L]

@Turbo4whl,

Oh yeah, thanks for the diagram of the symbols for those diodes. I was wondering about that!

 

[Raider L]

@Bextreme04,

Thanks! I thought I was off in the weeds on that. I do that a lot because I don't want to make any mistakes by being in a hurry. Especially when it comes to the dang wiring, that's all I need is something to go wrong because I didn't think it through enough.

 

[davetyp]

It had more to do with the poor electrical design of the older systems. The way these older truck electrical systems were designed had LOTS of EMI in the system and you could get significant surges in voltage as things turn on/off. When they went to EFI and digital sensors, they had to redesign the electrical systems to get rid of a lot of that interference so that the ECU could read the correct parameters without getting fried. This is why the EFI vehicles go to relays and fuses for almost everything. The factory GM relays will have a diode(or often a resistor) in the activation circuit to reduce the EMF spikes in the system. The older carbureted engines don't really care about voltage spikes or EMF, so they just used the cheapest and easiest to produce system possible. The reason they used a fusible link is because it will allow a large voltage spike over a short period of time without melting the link. A similar sized fuse will blow instantaneously when it gets that spike.

Thanks! That makes sense. I had in mind slo-blo 50 or 75 amp fuses... maybe those just weren't (still aren't?) made.

 

[Raider L]

@davetyp,

I was looking at my wife's Subaru and it's got some different kinds of fuses in it. But I don't know anything about them. And in the past when I've called the dealer about fuse designations on the covers of the underhood fuse boxes in the engine compartment, what they were, and what they went to, and they didn't even know. They just said they were "general fuses" that were just "general use". What the heck does that mean? They aren't even marked on the fuse box lids that's why I wanted to know what they went to. They didn't know. But, boy, some of them were pretty big. I thought about using one of them. But like @Betreme04 said, rather the wire take the hit and not melt. Better that than be going down the road and have a fuse blow and the truck die!

 

[davetyp]

@davetyp,

I was looking at my wife's Subaru and it's got some different kinds of fuses in it. But I don't know anything about them. And in the past when I've called the dealer about fuse designations on the covers of the underhood fuse boxes in the engine compartment, what they were, and what they went to, and they didn't even know. They just said they were "general fuses" that were just "general use". What the heck does that mean? They aren't even marked on the fuse box lids that's why I wanted to know what they went to. They didn't know. But, boy, some of them were pretty big. I thought about using one of them. But like @Betreme04 said, rather the wire take the hit and not melt. Better that than be going down the road and have a fuse blow and the truck die!

Hmmm... better that the truck die than something melt and catch fire. Those fusible links always seemed like a fire hazard to me... but I'm no vehicle electrical system engineer.

Pretty sure "general use" means "stop asking us questions we can't answer."