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Old 03-14-2011, 02:01 PM
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Default Save a switch using relays to help carry the load

This originally was published in Rodder's Digest June 2007 by Garry McWhirter and Larry Stanley

A scan of the article was email to me by keyser sose. I have retyped it. On the diagrams for this information: I worked from a PDF file that was a scan of the original article and some of the info was not very clear I did the best I could to get the information correct but there might be some errors.

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When a switch fails on a car, it can usually be traced to an overload situation. The traditional way of wiring switch s directly into the electrical system involves a direct current passing through the switch. If there is an electrical overload on a particular circuit, then that spike in amperage goes directly to the switch.

In many cases, the switch is not designed to carry such high amperage. This relay system directs the current through a relay with the switch, making the connection go to ground and thus completing the electrical circuit. The amount of current passing through the switch is reduced greatly and prevents overloading. By using the groundside of the relay coil, the voltage is carried through a switch that will be only 0.05 milliamps.
By reducing the electrical load, the switch will also last longer. This system will allow the use of smaller micro switches, which can be mounted in less conspicuous places on or under the dash. One thing to remember is that you should use a good grounding source in any electrical system.

Larry Stanley stopped by our booth at Oklahoma City last year and suggested that we check out his way of wiring street rods. His experience has included wiring system installations for limousine conversions full-time and hot rods part-time. He has used this system for over 18 years with no problems. We asked him to provide us with more information, so he sketched some diagrams that we studied intently. While some may view his system as overkill, we found it innovative. From a safety point of view, it makes good sense.

Stanley also told us that adding electrical components later is a much simpler task, especially if the vehicle has a finished inteČrior. Stanley gave us permission to pass his ideas along to our readers. We transformed his sketches through our illustrator so that you can view them and decide for yourself.






We have included diagrams for the most common electrical connections used in cars. The relay system detailed for the headlights and taillights should be of interest. The use of halogen headlights can cause switch failure, and the use of relays in the lighting system redirects the voltage through the relay instead of the headlight switch.

There are various other heavy-load circuits that can be wired with this same relay system. High-amperage applications, such as cooling fans, remote door locks, power windows, convertible tops and power-assisted trunk or hood lifts, are great examples. Another advantage of using this system is that original 6-volt switches can be used with a 12-volt system. The voltage passing through the switch can be measured in milliamps, thus saving each switch from an overload of amperage.



NOTE: We labeled the wiring colors within our diagrams to coordinate with Larry Stanley's sketches. These colors can vary according to the manufacturer, year, make and model of your particular application. These colors may also vary with aftermarket wiring kits.




Steering column
Above you'll see a diagram of the typical GM steering column turn signal wiring. We have assigned numbers to each wire and circuit to reference later diagrams in this article. Our wiring layout uses a standalone brake switch such as the one below, instead of wiring through the column. Each circuit will be connected to a relay that is connected to a power source. The relays are opened and closed through the operation of the turn signal switch on the column, horn button and brake switch. The run signal, emergency flashers and brake switch are wired directly to a grounded source. Operation of each directs the relay to supply positive power to the component. By using this method, the power load is placed onto the relays instead of the switches. Most switches are not rated for high amperage while the relays we use in this application can handle up to 30 amps. Each of the following diagrams details the wiring connections that are required for each function and component.







Starter Relays
From a safety standpoint, you should always use a neutral safety switch with an automatic transmission to prevent cranking a car with the transmission engaged in either reverse or forward gear. Either of these two wiring operations can be used separately or in conjunction. The neutral safety switch can be used as a standalone switch for activating the starter or as a switch to activate the hot-start relay. When using the neutral safety switch with the hot-start relay, the read wire that is labeled going to the starter should be connected to the hot-start relay that is coming from the ignition start. By using this relay system, the voltage or amperage load will be placed on the relay instead of the ignition switch or neutral safety switch.







Relays
Relays come in a variety of amperage ratings that are usually much higher than a normal operating switch. A relay works much like a switch except that completing the electrical circuit activates an internal switch. You are probably accustomed to using a switch to supply the positive power to the relay. In this electrical system, the switches used complete the grounding of the electrical circuit, thus activating the built-in switch inside the relay. Larry used relays and sockets from Streamline Hot Rod Parts and has included the part numbers from that source. There are many sources available to purchase these same components. The part numbers will vary between suppliers.





Attached Images
File Type: png brake-light-switch.png (10.4 KB, 41 views)
File Type: png headlights-park-taillights.png (46.6 KB, 41 views)
File Type: png turn-brake-switch-system.png (62.2 KB, 42 views)
File Type: png steering-columnl.png (51.2 KB, 43 views)
File Type: png horn-relay.png (26.0 KB, 42 views)
File Type: png neutral-safety-switch.png (45.7 KB, 42 views)
File Type: png starter-hot-start.png (37.4 KB, 41 views)
File Type: png generic-relays1.png (17.8 KB, 41 views)
File Type: png generic-relays2.png (13.5 KB, 42 views)
File Type: png generic-relays3.png (17.7 KB, 42 views)
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Old 03-14-2011, 02:12 PM
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Thanks a bunch freaky head shakin guy!!! I don't care what Donny says, you're alright!!
A tip of the hat to Centex too. If he hadn't asked the question, I woulda left this info in my library on the back of the stool (another advantage to bein single! ). I sent the PDF file to him, and he encouraged me to post it. I had to ask for help in getting it from a PDF file to here tho, which is where Rob came in. This one is a teamwork thing!

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Old 03-14-2011, 03:01 PM
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Rob, Keyser Sosa, and Centex,
Thanks for your team work on this topic! I'm about 38 watts short of a 40 watt bulb when it comes to auto wiring and relays. Looking forward to some good reading!

Doug
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Old 03-15-2011, 09:40 AM
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Added the drawings and moved it to the Electrical Drawing area.
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Old 03-15-2011, 09:59 AM
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Thanks Rob!

Doug
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Old 03-15-2011, 12:51 PM
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OUTSTANDING ROB!!!! take a couple six-packs out of petty stash!




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Old 03-15-2011, 01:56 PM
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Good info, guys!
Thanks for making it available, Rob.
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Old 03-28-2016, 03:01 AM
TherMilm
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Default Save a switch using relays to help carry the load

Hi Victor, me again.
As I recall the headlight switch is a pretty simple toggle as you noted. It goes left and right from a center position. Left is for parking lights, center neutral - no lights and right is headlights. The dash light rheostat control is oddly on another switch entirely.
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