Over the next few weeks, I'll be running some equipment in the car that will use more amperage than available from the cigarette lighter/ power sockets in the car. The equipment will use a 500 w inverter and, up until this point, I was popping the hood and hooking up the inverter to battery via alligator clips. However, soon I will be commuting and need the equipment to operate while in transit so no hood up. I tried to find a spot to run a positive wire from the battery through the firewall today, but I had difficulty finding a suitable place, so I decided to ask here for any possible suggestions.
Buy a step dril and a suitable grommet, and a bit od silicone caulk. Find a spot on the firewall that does not interfere with anything either inside or out, and drill a hole. Install the grommet with a dab of caulk in the groove, pull the wire through the grommet, and seal around the wire with a dab of silicone. Connect the wire to the battery / positive power distribution point using a 50 amp maxi-fuse in an inline fuse holder. If you want it to shut off with the key, also install an accssory relay rated at 50 amps continuous or better, and connect the coil to a switched power connection under the hood. If you want to be able to switch it manually from inside, connect the one side of the coil to the power(battery) side and run a light wire along with the heavy wire up to the dash and install a switch with the second terminal connected to ground, and connect the underhood end to the other side of the relay coil. A headlamp relay might work, but I'd use one of the continuous rated solenoid or accessory relay like a Napa/Echlin part#AR158 (gm 15555675 or d-1793) Looks like a starter solenoid, but designed for continuous use. A starter relay has too low resistance on the coil and will overheat and possibly burn out in constant-on use.
It should be an easy task to run what is essentially a set of battery temrminals inside the car.
First, you will need the appropriate fuse mounted as near to the positive battery terminal as is possible. Not convient, possible. You might have to change out the positive terminal on the existing cable, or get an adaptor that allows the existing cable to connect, along with the new cable you want to install. On my F150, the cable from the battery goes to a power diustribution block that has capacity for additional connections, your Taurus/Sable might have an equivalent power block.
Search the firewall for a grommet, this is a good location to push your power cables through. You can remove the gormmet and make a hole in it for the wire, then put the grommet back into the hole after you run the cable.
Once your cable is inside the cabin, then you can connect your inverter. You should not make the battery connections until you get the wire routed as you want it, and determine where the inverter will be located. After you have all of this figured out, then you can make your battery connections -- do the positive first, then the negative last.
You can pick up the negative from a suitable sized screw or bolt on the engine, or on the body of the car. It is not necessary to get ground from the battery, but this may be the most convenient. You might find that there is electrical noise, this can mean that the ground point has resistance -- paint is a source of resistance.
If any of this makes you uncomfortable, then any alarm installation shop should be well equiped to handls this for you. It is easy. You have to calculate the wire size and fuse based on the load. It is okay to have too much wire, but you will want the fuse to be rated properly for the inverter. Many inverters have the wire for making the battery connections, so you might not have to calculate anything, you only need to find a route for the wire to take through the firewall.
Being a 500 watt inverter, a 50 amp circuit will be more than adequate. 50X12 is 600 watts. When you are running the engine it's coser to 14 volts, so 50X14=700 watts. Upsize one wire size for your length to be safe. #6AWG is just on the light edge -if you are running that inverter at full load. It's good for 55 amps in a bundle - more in free air.
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