Your diagram shows the alternator and the power to the fuse panel connecting to the switched side of the solenoid. It can't work that way, there is no way to get power to the On/Off switch or to the key switch. Look at it again. Follow the path from the battery to the solenoid. What happens next? Nothing. Your alternator and your "Constant power" supply need to connect to the same side of the solenoid as the battery.
Oops It does look like it is going to the wrong side in the diagram. It is however on the other (battery)side. I will need to make that clear. This is what happens when you just got home from a Christmas party Thanks for the catch.
YES IT IS! God gave you the ability to understand it, I got cheated. I'll be doing brain surgery long before I wire any of my cars. Bob
Bob, get us a case of Miller Lite and a day and I’ll have you wiring the space shuttle. Nothing to it. Let me know when your ready. Bones
The diagram I showed is the way a passenger power window is controlled by both the passenger side switch and the driver side switch. I don't see how you could do it with diodes, because we are reversing polarity, current needs to flow both ways.
Thanks Pinball. Well I got it working back in September. I put in two toggle switches. One toggles the power between the remote control board and the second toggle switch. The second switch operates the motor when the first switch is in the position that powers it. Basically I think what you diagrammed.
I used an UP relay and a DOWN relay . Have the up wire from window switch and up wire from remote box on one relay. Down wire from window switch and down wire from remote box on the down relay. That way the two circuits are separated. Hope that makes some sense. Phil
Crude I know, but here is the current flow with the switch activated and the relay module not activated Chris
As my first post on the forum, I'll resurrect an excellent discussion about automotive wiring. First, thanks Crazy Steve for all the time and effort you put into the thread. I'm preparing to wire completely from scratch my project. I'm not new to wiring and electrical theory, but some things in this thread have me scratching my head incredulously or at the very least perplexed as to how the theory actually functions in historical practice. For starters, I completely understand that modern power accessories (power windows, locks, seats, a/c, etc.) and ignition systems put into older vehicles require the type of system Steve describes in example #4 (post 168). No confusion or doubt there. However, I'm having trouble understanding the reasoning behind needing such a system for the vast majority of traditional hot rods out there. I want to use an example to clarify my confusion: My lumber/parts-getter is a bone-stock, unadulterated, paint-peeling 1978 Ford. The factory alternator puts out 63 amps, and I've never had charging/powering issues with the truck. I've researched the electrical components, taken some amp readings, and have come up with the spreadsheet below. Using Steve's instructions, the truck should have an alternator capable of at least 77 amps and ideally 80 amps. Unswitched Continuous Headlights (2) 9.0 amps Taillights (2) 1.4 amps License P. Light (2) 1.4 amps Front side lights (2) 1.4 amps Dash lights (6) 1.8 amps Switched Continuous Ignition 11 amps Radio 7.0 amps Heater blower 15 amps A/C blower 10 amps Wipers 6.0 amps Total Continuous Load: 64 amps Total Continuous w/ intermittent factor of 13 amps: 77 amps Alternator requires at 125% of total continuous: 80 amps Unswitched Intermittent Brakes (2) 5 Emergency (4+dash) 10.6 Dome Light 0.3 Cigarette Lighter 16 Horn 12 Switched Intermittent Front turns (2) 5 amps Rear turns (2) 5 amps Backups (2) 5 amps In comparison, my build is very similar to the '78 minus the a/c but adding an electric cooling fan. After using Steve's instructions and calculations, I would need an alternator putting out at least 80.5 amps and ideally 85: Unswitched Continuous Headlights (2) 9.4 amps Taillights (2) 1.4 amps License P. Light (1) 0.7 amps Dash lights (10) 3.0 amps Switched Continuous Ignition 10 amps Cooling Fan 20 amps Radio 7.0 amps Heater blower 10 amps Wipers 6.0 amps Total Continuous Load: 67.5 amps Total Continuous w/ intermittent factor of 13 amps: 80.5 amps Alternator requires at 125% of total continuous: 85 amps Unswitched Intermittent Brakes (2) 5.0 Emergency (4+dash) 10.6 Dome Lights 0.9 Cigarette Lighter 16 Horn (1) 6.0 Switched Intermittent Front turns (2) 5.0 amps Rear turns (2) 5.0 amps So my ultimate questions: 1) How can a factory designed, unadulterated truck run fine with no electrical issues on a 63 amp alternator and factory 30 amp ignition switch when using Steve's math it requires an 80 amp alternator and a relay to not overload the ignition switch? 2) With the '40 coupe build drawing only 3.5 amps more continuous than the '78 pickup, why couldn't the '40 coupe run safely using the same 63 amp charging system and 30 amp ignition switch design as the pickup? 3) To clarify, I'm in no way disagreeing with Steve's process, and I may very well follow his suggested relay system with a 90 or 100 amp alternator for the project; I'm just curious to hear from others and hopefully Steve why Steve's process doesn't seem to match 1960's and 1970's design practice on minimally accessories equipped vehicles that run to this very day with no issues. By the late 1960s and through the 1970s, just about every US vehicle would have used at least approx. the same amount of power as the '78 example above (minus the 10 amp a/c blower in many packages). My deductive reasoning is that the manufacturers did not calculate required charging capacity the way Steve recommends. Similar to Steve's analogy of a residential main panel, it would be an extremely rare situation to have every circuit in a house turned on at the same time, overloading the panel, just like it will be extremely rare for someone to drive for a prolonged amount of time with all the continuous loads on at the same time, draining the battery.
What Steve told you is optimum , what it “ should” be. What the OEM figures is what can they get by with and still work, to save money. You save $10 on every car and sell one million cars, that’s $10,000,000 in profits. How the OEM always got by with seemingly going against proper guidelines with small wire has always amazed me! And as for the size of the alternator, depends on how long you drive your vehicle. Shorter trips require larger amps. You also are not usually going to have everything thing on all at the same time. PS: I’ve been meaning to ask..... where is Crazy Steve? I haven’t seen any post from him in a while! Hope he’s OK. Maybe he will chime in here? Bones
Like Crazy Steve mentioned, think about how you are going to lay out the wiring in the vehicle. During my 50 years working on vehicles the most common problem I found was poor grounds. Do not trust a component to have a good ground. Bodies are insulated from the frame. Run separate grounds to the engine, body and lights. Ground the battery near the starter. Make sure the generator/alternator has a ground. IF you are grounding a component, make sure you scrape or sand off the paint under the connector. Keep the wiring harnesses away from heat and moving objects. Using a 4-10 wire connector to separate a branch harness from the main harness to allow for repairs. Don't mix LEDs with regular light bulbs unless they have the built in resistor.
Thanks for the replies. I see that Crazy Steve was active January 14, 2020, so hopefully he can shed some more light on my post questions. I imagine I could safely run my setup off a 63 amp alternator and a stock harness design, but bumping up to 100 amps, a relay design, and #4 feed is only $120 in parts more and would certainly be solid and allow for ample room to add circuits if I ever wanted. In the meantime, is this schematic I drew up accurate regarding Steve's large relay system and the additional posts about protecting the #4 relay feed with a circuit breaker (rather than a fusible link)? Again, I'd be using a 100 amp alternator, and my system at 125% of total continuous loads would be drawing 85 amps. I like the circuit breaker idea because of the reset ability if I'm stuck out in the middle of nowhere and also because I could trip the breaker when parked as a theft deterrent.
Yes that circuit will work as long as your acc terminal on your ignition switch is energized on the run and acc position. Most are. The only possible problem I see is your unswitched and switched loads combined are more than your circuit breaker, but the chance of having max load on both at the same time is kinda remote. Bones
I run a 63 amp alternator on my Ford, with the added electric fan (on a thermostat) I could use a little more. With the selection of wiring kits, there are many good harness kits to choose from. My car is bare bones and a 14-circuit harness did the trick. If you want more accessories a 21-circuit kit may be the way to go.
Just to be clear before I start my project this seems be the way route when using seperate unswitched and switched fuse panel, Since the system will be using a large relay I will not need to use little cube relays for the fan, headlights or horn correct? Also since my electric radiator fan only draws 5 continuous amps can I use a 7.5 amp fuse or should I still use a 30a fuse? Same question for the fan wiring since the large really is used can I size the wire based on the 5 continuous amps or the 30amp initial draw? Thanks Crazy Steve this has been an extremely helpful thread.
OK, so I'm in the process of installing a stereo system and was about to attach the ground wires from the radio and amp to the common ground I use for the dash. When I took out the screw that fastened all of the ground wires to the body, I found that the insulation on the ground wire from the battery to the dash was melted! Thankfully, I caught it before something bad happened, but what would cause that? There are probably 6 ground wires from various dash components that use that common stud. The ground wire from the battery is 12 gauge. I had it run from the dash through the firewall and wire-tied to the rest of the wires in the (Painless) harness that run to the battery/circuit breakers. Wherever I had it wire tied to the rest of the wires, the insulation on the ground wire was melted. I obviously did something wrong. Looking for advice please. Thanks, Dave
Remember that current flow is the same on the low side of the circuit as the high side so if using a common ground point with one wire to the battery that wire has to be of sufficient size to flow enough current to handle everything that is grounded there. Sent from my iPhone using H.A.M.B.
Thanks. So, was that ground wire a bad idea? Should I just spread the grounds around rather than to a single stud? The sheetmetal that secures the dash should be grounded because the body is grounded to the battery, engine and frame. Sent from my SM-G930V using The H.A.M.B. mobile app
Ground wires need to be heavy gauge... when in doubt, add another ground to the dash from the frame. Use heavy gauge... 3 gauge would be good. Be sure all connections are CLEAN bare metal. I use dielectric grease to avoid corrosion further on down the time line. Be sure to have a heavy gauge ground from battery to frame, frame to body, frame to engine. Using a couple extra grounds further back from frame to body never hurts. Remember; short cuts are never short cuts!