@Bridenour , Yes, headlight switch power to #56 will make the flash to pass feature work, as shown in post #521 above.
@reyn , instead of a toggle switch, why not just have a separate momentary switch button for the dimmer latching relay? A starter button, an accessory column mounted horn button, etc. I used a repro motorcycle kill button. Seems safer than deactivating the horn, which is a safety concern.
So I have seen a few posts regarding master fuses, mega fuses, fusible links etc. I ran across these on Amazon and wondered if any one has considered one of these in their system? They seem user friendly, easy to reset and install and a available in many ratings. I have no experience with one - just throwing it out there for thoughts. https://www.amazon.com/dp/B08ZXK1KY...abc_X0S52S39HVK305N2323R?_encoding=UTF8&psc=1
My motorhome has a ton of these on it! They work and I have had no problem resetting one occasionally. So they should work great on any application if selected properly. Bones
Another question for the experts: I have seen in wiring diagrams fuses between the battery and the component side of a relay (terminal 87B) and then ones with and without an additional smaller fuse for the corresponding switch between it and the battery. Are these necessary for the switches? If so, do you keep them separate or gang some together to reduce the number of fuses?
Every circuit in a car needs to be protected with a fuse or circuit breaker. Usually the huge stater cable is not, but it is carefully routed as to avoid problems. And putting a circuit protector in that circuit would be difficult. Grouping the fuses in one spot will add wire to the circuit. While not terrible, not really desirable! Bones
Ok, the protection for each circuit makes sense. So for one containing a relay you would need 2 due to the switching power circuit and the component power circuit. Still trying to figure out my truck rewiring scheme and I’d like to use relays in the major power draw circuits.
Not sure what 87B is; but the battery side of the relay (30) is usually fused appropriately for the component without an additional fuse between the relay output (87) and the component. Each relay control circuit does not require a separate fuse; but should be fused somewhere. Such as one accessory fuse can operate several relays, either directly or thru a switch, one ignition fuse can control several relays; again either directly or thru a switch, and one battery fuse can control several relays always thru a switch (except maybe a radiator fan if you want it run for cool down when engine is shut off).
Ok, I think what is desired is to have the switch circuits fused in some manner, whether separately or some together as long as they are fused. Fuses are needed for these circuits no matter what.. Thanks for the info!!
There're multiple ways to configure relay control circuitry, not all will require fuses on the control side. The simplest way is to switch the relay coil ground. Get your relay coil power off the incoming circuit power with a short jumper to the coil connection, then run a single wire from the other coil connection to your switch with the other side of the switch grounded. This is commonly how horn relays are wired. The downside is if the wire or switch fails to ground, you lose control over the circuit. If you ever had a horn start blowing uncontrollably, this is probably why. Size the jumper wire at about 80% of the circuit fuse size or more for adequate overcurrent protection against shorts to ground. Most OEM horn relays have this jumper factory installed internally and are a good choice if using this method. No control fuse needed. In terms of how many wires are needed to control the relay, this will be the least amount. A similar way is instead of installing a jumper at the relay, extend the wire to the switch for control power then return to the relay coil, grounding the other side of the coil at the relay. Again, size the switch wire at about 80% of the circuit fuse size, no fuse needed. This would be my preferred method if controlling only one or two relays or if the relays are located in multiple places. Got three or more relays in one location? Then a single control circuit becomes attractive as it reduces the total wire count needed. One power wire common to all relays, then switch legs to each device. The least complicated method here is to size the control circuit fuse/wires at 250% or more of the total coil load (most relay coils only draw about 20 Milliamps) and one fuse will protect it all. The reason for this is if you do have a relay coil fail, it won't knock the entire control circuit off-line and shut down all relays. Relay coils are wound with very fine wire and will melt 'clear' at relatively low current numbers in the case of a fault. Remember, the fuse is there to protect the wire, not the device. The single-circuit method isn't always possible or desirable to use however, particularly with lighting circuits. For safety reasons these circuits are almost always kept separate, you wouldn't want your dash lights taking out the headlights too. Other circuits, you'll have to decide the importance of each one.
The basic idea is that the fuse(s) are there to protect the wires, and that means the fuse size is chosen to match the wire size. This means you can have for example a 30A fuse feeding six switches, each switch feeds something using under 5A so the total load is less than 30A when they all are on. In this case you need to use wire capable of handling 30A through the entire circuit, which is a waste of money as most of the wire never will see more than 5A in normal use, but as it is fed through a 30A fuse the wire needs to be able to handle 30A. You can make the same basic circuit but put an extra 5A fuse on each of the six wires right after they split of the single feeder wire, and just use cheaper, smaller wire that can handle 5A in the rest of the circuit. Now the small wires are protected by the 5A fuses, and the bigger feed wire is protected by a single 30A fuse. Lots of ways to skin a cat, but the basic idea is that no wire in the system should be unable to withstand the current the fuse(s) feeding it can supply. Big wires go with big fuses, small wires go with small fuses, big fires go with no fuses.
I won't disagree but I will point out that it's not necessarily true for relay control circuits, which is what I was specifically referring to. On the power side feeding the controlled device, absolutely true. But run a large current through a relay coil and it'll give a very good imitation of a fusible link.... clearing the short.
Yes, in general low risk on the ground side of a relay control circuit. But there's also the possibility of another metal object touching the poles on the relay, making an exterior short past the relay coil.
That's why if it's a plug-in style relay you should use a 'base' to ensure that the connections aren't open to this. If using bolt-connection relays, those will be higher-current circuits and care needs to be taken in location/mounting to prevent this. If you start using fuses everywhere for every possible circumstance, that defeats the purpose of having a central fuse panel. And also highlights the dangers of using the smallest possible wire. Personally, I won't use anything smaller than #14 except in very limited places where it will be intrinsically safe.
Question regarding wiring in a breaker like I mentioned earlier in post #543: Here is a basic schematic I made up and I was wondering where the alternator power wire got connected. Right now mine is wired through the ammeter gauge which I will be removing. TIA.
If it were me, with the information I have I would put it at the battery side of your master breaker.
If the breaker is near the input power source, why does it need a fuse? Isn't that the purpose of the breaker?
The breaker needs to be as close to the power source as possible, to protect the wires on down from the breaker/ power source. Bones
I see there's still confusion about the use of these large breakers/fuses for fuse panel feeds and alternator output... These are commonly installed for 'safety' by the uninformed but unless certain rules are followed basically do nothing. First, the cardinal rule with overcurrent protection is it's there to protect the WIRE. So a 100 amp fuse should have at least #3 wire connected to it so that the wire's ampacity matches the fuse size. A 150 amp would need 1/0 wire. If you've used diversity to reduce the wire size (which is acceptable), this means that you basically have little or no overcurrent or overload protection. Remember, both of these wires DON'T have a 'set' current applied to them; it will vary by what the loads of the various branch circuits in operation are. If those are properly fused, any issues there will be cleared by the fuse on that circuit. But you need a large-value fuse or breaker because you must size it to the MAXIMUM current that would be seen, even if only briefly or suffer nuisance tripping. Too-large fuses usually equals fire.... That leaves catastrophic short circuit protection. Now, in the event of a major accident, it's possible that one of these wires could be pinched between two pieces of grounded metal. Will that ensure that the fuse/breaker will clear the short? Maybe, maybe not. Keep in mind that at 100+ amps, that's arc-welding current. Turn your wire-feed welder to 100 amps or more and you'll just burn holes in sheet metal. All the fuse or breaker knows is it hasn't reached trip current yet. This is even more likely in the event of the wire chafing against something, wearing a hole in the insulation. The most likely scenario is burned-away sheet metal and the melting of individual wire strands until the wire breaks or has its cross-section reduced enough that it heats up and catches fire. To the best of my knowledge, the OEMs never fused these wires (certainly not in the HAMB era), for these reasons. As long as you route/install these to protect them from 'normal' physical damage, the branch circuit fuses will give all the protection you need, plus eliminating the additional failure points of the fuse/breaker install.
Interesting points for sure. I was looking at it as a last line of protection, somewhat close to the battery like a megafuse or fusible link. Maybe if all of the regular circuits are wired and fused properly this isn’t really needed as long as the power feed wire is sized accordingly, routed properly and protected physically? I know before without a breaker I didn’t have any issues other than when I had one circuit overloaded (I know a lot better now) and blowing fuses but that has since been corrected. I appreciate all the info on this!
That's it right there. These large fuses/breakers do have their uses, but generally not on cars and light trucks. Buses, fire trucks, high-end motor homes, other commercial vehicles and mobile equipment is where these may be applied. The one exception would be if installing a melt-your-head audio system with one or more monster high-current amps but those will need a dedicated system separate from the 'normal' wiring anyway, with the only interconnection likely being an activation wire from the head unit. The car audio industry is where these came onto the radar of car hobbyists, unfortunately too many have mis-applied them.
Well I’m not planning on melting my head!! Thanks a lot for the info, I really appreciate it. Sounds like I was going for an unnecessary step and like you said potentially more connections and a breaker that would trip unexpectedly. Thanks again!!
Had to deal with a few corroded connections lately. What exactly does CRC Contact Cleaner do, remove corrosion, dirt? Don't see it removing the green junk. Is there an all in one product that does it all?
I've used contact cleaners for years, for cleaning pots and switches in electric musical instruments and amps, home stereo components, etc. These are all things that live indoors and don't experience the sort of green corrosion that vehicles might. I think connections in cars are going to require physical sanding, scraping, etc., a contact cleaner aggressive enough to clean "green junk" would likely destroy smaller pots and switches.
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