Wiring questions from a newbie

Discussion in 'The Projects Forum' started by dmc0162, Sep 20, 2008.

  1. dmc0162

    Thread Starter Active Member

    Dec 13, 2007
    I just have a question about wiring since I am replacing some of the factory switches in my car with 25A toggle switches. The switches are for things that have a fuse less than 25A, and control things such as the windshield wipers, door locks, and radiator fans. Can I use thicker gauge wire than stock to wire the new switches in without any problems? And do I use the same fuse?

    Most importantly, how can do I know how much current each device draws? Do I just look at the size of the fuse for that circuit and determine it that way? Thanks
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    Yes, the switches and heavier wire will not create problems, except for the added bulk.

    The switch and wiring has to handle the amount of current the fuse is good for, so that is the way to determine the switch contacts and wire gauge. More than just enough is always a good idea.
  3. Soupling


    Sep 19, 2008
  4. cumesoftware

    Senior Member

    Apr 27, 2007
    Indeed, as beenthere said. You will have no problems when using thicker wire. If the former wire gauge supported the currents inside your circuit, the thicker wiring will hold even better.
  5. thingmaker3

    Retired Moderator

    May 16, 2005
    If you can find rated information on the device (horsepower, watts, whatever) you can calculate the current drawn.

    If not, you can put an ammeter in series with the device. Make sure your meter is set to read more current than you expect. (I.E. use a 30A shunt.)
  6. gerty

    AAC Fanatic!

    Aug 30, 2007
    Before you take anything apart look carefully at the application. For example door lock switches are different from the drivers side to the passenger side, the drivers side being the 'master'. Wiper motors on most vehicles switch on/off with the ground and not the positive. Also they are two position, high/low speed.
    What you want to do is feasible, just watch the application..
  7. dmc0162

    Thread Starter Active Member

    Dec 13, 2007
    well, what are the main differences when you switch the ground and not the positive? What are the reasons for doing this?


    Also, I wouldn't try this, but I just wanted to know what would happen if you have a circuit with a high current, and you used very thick wire (the CORRECT wire) for the positive, but on the negative you used extremely thin wire (24g). What would happen?
  8. SgtWookie


    Jul 17, 2007
    AWG 24 is only good for up to about 3.5A. After that, it will get very hot and melt.
  9. Mr. Beck

    New Member

    Sep 19, 2008
    You'd get a toasted wire. The same amount of current is flowing through all parts of the circuit- see Kirchoff's Current Law.
  10. chrissyp

    Active Member

    Aug 25, 2008
    be carefull of the wire insulation type. you have heat and oil in the engine bay, some wiring coatings will not tolerate either or both.
  11. gerty

    AAC Fanatic!

    Aug 30, 2007
    Code ( (Unknown Language)):
    1.   well, what are the main differences when you switch the ground and not the positive? What are the reasons for doing this?    
    On the wipers, for example,the ground is switched so that when they are turned off they go to the 'park' position,that's the lowest position where they're out of sight. The park switch is built into the wiper motor asssembly, it maintains the ground connection until the wipers are out of sight. Without it the wipers would stop as soon as the switch was turned off, usually in the middle of the windshield.The dome lights also use a ground switching scheme, when either door is opened the dome light gets grounded. The headlight switch,usually when turned, puts a ground on the dome lights(but not the headlights). Like I said you have to be careful..