Junction block power

Discussion in 'Electrical & Audio' started by Wwiifan, Apr 20, 2017.

  1. Wwiifan

    Wwiifan Junior Member

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    Where does the junction block on the firewall get its power from? The batt/ alternator or fused from the fuse block? Got a wiring diagram? Thanks
     
  2. dougbert

    dougbert Full Access Member

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    It gets its power from the firewall bulkhead connector, circuit 2-RED. Circuit 2-RED comes from the battery to the firewall connector and then inside and Circuit 2 comes back out and goes to that HVAC junction block

    would help to know the year you are talking about
     
  3. chengny

    chengny Full Access Member

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    Says 1983 - but it doesn't really matter - all model years are layed out the same:

    Where does the junction block on the firewall get its power from? The batt/ alternator or fused from the fuse block? Got a wiring diagram?

    The JB uses no power, it is essentially a terminal strip. But I know what you mean.

    The short answer to your question is: From the battery.

    But it isn't a straight shot from the battery positive terminal to the line side of the FW JB. To get that point, there must be continuity:

    1. From the battery positive cable to the "B" terminal on the starter solenoid
    and then

    2. Through a fusible link. That link is located very close to the solenoid "B" terminal:


    [​IMG]
     
  4. Wwiifan

    Wwiifan Junior Member

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    Thanks for the help and diagrams guys. On to the next problem. I got the led dome light, lens, and chrome bulb housing from LMC. I can't find the bulb socket anywhere. Oreilly comes up with a tube type bulb. And no socket for it either (not that it's right anyway). I guess it originally took a 1004 bulb. Anyone have a link or bulb socket part number for the 1004?
     
  5. Craig 85

    Craig 85 Full Access Member

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  6. chengny

    chengny Full Access Member

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    What is the base configuration of the LED bulb that LMC provided. As you already know, up to 1984 the factory bulb was a 1004. That's a BA15d base. Google "ba15d socket" and you'll have plenty to choose from.

    The biggest problem with this modification won't be fitting the bulb into the socket, it will be finding a socket that will fit snugly into the mounting hole.




    What happened to the original socket at the end of the harness? If it's still there, use that.
     
  7. 75gmck25

    75gmck25 Full Access Member

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    When you install the dome light, remember that both the positive terminal (little nub inside the socket) and negative terminal (the socket) are insulated/floating from ground.

    The courtesy light circuit has all devices/lights always connected to power, and is grounded when you open a door or turn the headlight switch counterclockwise. This is the opposite of most other accessories where the ground is always connected, and power is switched. If you happen to ground the courtesy light socket to the housing or to the truck, the light will stay on all the time.

    Bruce
     
  8. chengny

    chengny Full Access Member

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    I'm fairly certain that a 1004 lamp is a double bayonet contact base (BA15d) - and would use a two-wire/two-contact socket. In that case, the socket body would be only used to secure the bulb and wouldn't be part of the lamp's electrical circuit.

    [​IMG]

    [​IMG]
     
  9. 75gmck25

    75gmck25 Full Access Member

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    Yes, you are right. I forgot about the double contact base in that bulb. It does not ground through the base, but through the 2nd contact.

    Bruce
     
  10. Wwiifan

    Wwiifan Junior Member

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    Thanks for all the responses. First of the truck interior was gutted so no existing bulb socket. Second I guess I didn't look hard enough in the LMC catalog since I missed their socket listing. But $19.95 plus shipping? No thanks. Third thanks for the clarification on the double contact and the base not being the ground then. Fourth, I guess the challenge will be to find a socket that fits the lens housing correctly.
    Anybody out there actually buy one and have a part number? Would save me some time.
     

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