Dash wiring

Discussion in 'Technical' started by Tumbler, Aug 9, 2020.

  1. Tumbler

    Tumbler Member

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    I'm planning to hook up some gauges and a new radio, so I've been trying to figure out the wiring under the dash. I'm looking for some good sources for continuous and switched power, along with ground. Getting up under the dash I discovered some differences from the wiring diagram as well as some modifications. There's a lot of wiring that splices in the current dead radio.

    All of the ground wires I see in the diagram are black. So far I've been failing to locate any black wires under the dash.

    I'm guessing that the best source for continuous power would be the cigarette lighter. In the wiring diagram, the wire for this comes from the fuse box, goes to the hazard flasher, and then branches off to the cigarette lighter and clock connector. In my car there's no wire branching off of the hazard flasher. It wasn't cut from the connector, it just doesn't exist.

    I also found a wire wrapped around one of the ends of a fuse. I followed it, and it runs up to the cigarette lighter. It also has the radio spliced into it. In the photo it's white wire going into the fuse box. The fuse it's wrapped around is 14A, and it should be for the dome light and ignition buzzer. I'm thinking about splicing this wire into the blue/white wire that runs to the hazard flasher. Is this a good idea? I'm wondering if that wire is missing for a reason, and if the wiring in my car might be arranged differently? This car is a 73 with air conditioning.

    I included some pictures of the wiring diagram and how it's been changed for clarity.

    WIN_20200808_17_10_25_Pro.jpg wiring.png wiring_modified.png
     
  2. mojo

    mojo "Everett"- Senior Citizen Supporting Member

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    I added an aux. fuse box for continuous power exited directly from the battery via a relay. I don't like adding any aux wiring attached to the fac. fuse box. Did the same for switched power.
     
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  3. Tumbler

    Tumbler Member

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    That sounds like a good idea. That would be a bit more work than I was anticipating . I'd have to put a hole through the firewall. The one I have is at capacity with wires and a vacuum hose.

    The cigarette lighter as it is now managed to be fine with a 500 watt power inverter. The biggest thing I ran on it was a pump for an inflatable mattress.
     
  4. smegnl

    smegnl Roger Saffle Supporting Member

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    care to expand on the relay part?
     
  5. mojo

    mojo "Everett"- Senior Citizen Supporting Member

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  6. Tumbler

    Tumbler Member

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    I've been looking into this a bit, and unfortunately I'm a total novice with electrical stuff. I'm not clear on how you would use a relay for continuous power. The relays I'm finding will send power from the battery through one pin when off, and then switch to the other pin when on. I was hoping to find one that would have continuous power for one pin, and switched power for the other.

    Also, what size fuse would one want for power coming off the battery? I'd be using the continuous power for a clock gauge, radio memory, and power inverters through the cigarette lighter. I'd assume the relay would do the job of getting the battery voltage down to 12V.
     
  7. mojo

    mojo "Everett"- Senior Citizen Supporting Member

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    1.) If you don't have a switch between power source and relay, power to whatever your powering will be continuous.
    2.) Fuse rating/size will be determined by what total current draw your adding or intended. There are online guides as to what each automotive accessory draws, giving an idea of what size fuse required and what size/rating wire to complete the circuit.
     
  8. RMiller

    RMiller My name is Rick

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    A relay is just a swiched switch, isn't going to change voltage. For all the items you listed I wouldn't worry about using a relay, save that work for the heavy amperage circuits.

    For the clock and memory circuits I would say 3.5-5 amp fuse tops. Not sure on the power port, I would look at the fuse sizes on your daily driver and see what it uses. Just make sure your wire size that's appropriate for the fuse size. If the wire is only good for a 20 amp load on a 30 amp fuse that wire is failing before the fuse pops.
     
  9. Krazy Comet

    Krazy Comet Tom

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    For large draw circuits such as power windows, seat etc, the factory connected a lead with fuse link directly to solenoid battery connection. A relay can easily give a switched power source, constant requires direct wiring to battery.

    I have a seven circuit Painless fuse box in my Comet, provides three switched(via relay) & four direct circuits.
     
  10. Tumbler

    Tumbler Member

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    I'm into this setup: http://mmb.maverick.to/resources/auxiliary-fuse-box-for-aftermarket-add-ons.254/

    I've been looking at fuse boxes with 6-8 circuits, and reading up on what's necessary for all the wiring. Initially I think have one fuse for continuous power, and two others triggered by relays for switched power and lights. I'll have some extra circuits for future add-ons like off road lights and a CB radio.
     
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