Adding an outlet to the back of my 87 4Runner - Need Help
05-12-2009, 06:51 AM
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Adding an outlet to the back of my 87 4Runner - Need Help
I am wanting to add a cigarette lighter to the rear of my 87 4Runner. What wires would you guys splice in to? I thought about splicing into the deck light, but i would really like to have constant power to the plug.
05-12-2009, 01:55 PM
#5
I tapped into the fused power wire that I ran to my powered trailer light converter, though many of those converters don't have a power wire running back to them (HD version, I guess).
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05-12-2009, 07:04 PM
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For a power outlet, I'd run 8 gauge (I know, overkill but...) from the battery with a 20 amp self resetting breaker near the battery.
If I were doing an inverter in the back, I'd hard wire the inverter in and use the next larger size wire the inverter requires with an appropriately sized (based on inverter requirements) self-resetting breaker up front... but then I would probably also have a relay so the inverter was off with the key off so the battery doesn't drain.
If I were doing an inverter in the back, I'd hard wire the inverter in and use the next larger size wire the inverter requires with an appropriately sized (based on inverter requirements) self-resetting breaker up front... but then I would probably also have a relay so the inverter was off with the key off so the battery doesn't drain.
Last edited by abecedarian; 05-12-2009 at 07:05 PM.
05-13-2009, 07:41 AM
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Some inverters have a Battery saver feature that automatically shut off when the batt. starts to drop off so you can usually get at least 1 start out of it but the relay is a good idea too...
Def. run separate wires back to the batt, with a fuse/cb... If you're planning to add an inverter down the road go with #8 AWG min. if you just want to run a 12V outlet then #10 AWG will do get the fine stranded stuff and it will bend easily to get you through to the Batt.
You want to use the heavier gauge wire in this case to reduce the resistance and resulting "line losses" this will put more of the system's available power at the plug and also reduce the heating under load lessening the chances of shorts/fires caused by melted insulation. [It can happen]
Def. run separate wires back to the batt, with a fuse/cb... If you're planning to add an inverter down the road go with #8 AWG min. if you just want to run a 12V outlet then #10 AWG will do get the fine stranded stuff and it will bend easily to get you through to the Batt.
You want to use the heavier gauge wire in this case to reduce the resistance and resulting "line losses" this will put more of the system's available power at the plug and also reduce the heating under load lessening the chances of shorts/fires caused by melted insulation. [It can happen]
05-13-2009, 03:40 PM
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If you want to know what size wire you need for any circuit, it is possible to calculate the required size and have a safe and efficient circuit. Some basics to work with:
1. Wire has a constant resistance based on size and temperature. The chart attached shows resistance values for standard automotive wiring at appx. room temperature in Ohm's per 1000'. Divide the number in the chart by 1000 to get Ohm's per foot. Multiply the Ohm's per foot by the length of the wire to get total resistance.
2. The steel body of the vehicle has a resistance of the equivalent to 2ga wire and should be used as the return to ground unless you're using larger than 2ga wire. The attached writeup of a test I performed explains how I came up the the equivalent resistance of the body. (Toyota also uses the body as the return to ground for all chassis electrical equipment.)
3. Keep the ground wire for any electrical equipment as short as possible by attaching the wire to the closest grounded bolt or nut.
4. Determine how long the power wire will be and use Watt's Law and Ohm's Law, along with the wire resistance of the wire size you intend to use to determine how much voltage drop you will have in your circuit (see attached writeup). If you have .5v drop or less, the circuit will be safe and efficient.
5. Place a fuse as close to the battery as possible to protect as much of the wiring as you can. The fuse needs to be large enough to allow the maximum current your inverter and 12v outlet will use but still protect the wiring. The current that would cause a .75v drop in the circuit should be the maximum allowed by the fuse. This fuse would blow well before there was damage or a fire.
6. Bookstores have great books on automotive electricity that will take the mystery out of wiring. The one I reference is still available in stores and is great. Keep in mind that rules of thumb for household 110v wiring do not apply 12v automotive wiring--use the calculation or the wire size recommendation charts in automotive electricity books!
7. The wiring in the vehicle was sized to handle the loads Toyota installed and may well not be big enough to handle any added load. If you want to add electrical equipment to your vehicle, you should run a fused supply wire from the battery to a new fuse block you install under the dash. Painless Wiring makes great fuse blocks that can form the foundation for adding electrical equipment. Use the above method to determine the size of the supply wire.
1. Wire has a constant resistance based on size and temperature. The chart attached shows resistance values for standard automotive wiring at appx. room temperature in Ohm's per 1000'. Divide the number in the chart by 1000 to get Ohm's per foot. Multiply the Ohm's per foot by the length of the wire to get total resistance.
2. The steel body of the vehicle has a resistance of the equivalent to 2ga wire and should be used as the return to ground unless you're using larger than 2ga wire. The attached writeup of a test I performed explains how I came up the the equivalent resistance of the body. (Toyota also uses the body as the return to ground for all chassis electrical equipment.)
3. Keep the ground wire for any electrical equipment as short as possible by attaching the wire to the closest grounded bolt or nut.
4. Determine how long the power wire will be and use Watt's Law and Ohm's Law, along with the wire resistance of the wire size you intend to use to determine how much voltage drop you will have in your circuit (see attached writeup). If you have .5v drop or less, the circuit will be safe and efficient.
5. Place a fuse as close to the battery as possible to protect as much of the wiring as you can. The fuse needs to be large enough to allow the maximum current your inverter and 12v outlet will use but still protect the wiring. The current that would cause a .75v drop in the circuit should be the maximum allowed by the fuse. This fuse would blow well before there was damage or a fire.
6. Bookstores have great books on automotive electricity that will take the mystery out of wiring. The one I reference is still available in stores and is great. Keep in mind that rules of thumb for household 110v wiring do not apply 12v automotive wiring--use the calculation or the wire size recommendation charts in automotive electricity books!
7. The wiring in the vehicle was sized to handle the loads Toyota installed and may well not be big enough to handle any added load. If you want to add electrical equipment to your vehicle, you should run a fused supply wire from the battery to a new fuse block you install under the dash. Painless Wiring makes great fuse blocks that can form the foundation for adding electrical equipment. Use the above method to determine the size of the supply wire.
Last edited by bugs1961; 05-13-2009 at 03:50 PM.
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