Power inverter question

1. I use mine either in a Chrysler Sebring or off a Power-Station (a portable 12 volt battery system for starting cars, charging, power outages, etc from Costco).
2. You have realized an important issue here. If you plug a 150 watt converter into a cigarette light outlet rated at 120 watts it will either blow a fuse or cause some serious damage to the inverter, the outlet, the outlet's wiring or something else. See 3 for how to avoid this.
3. Most inverters provide a set of alternative cables for direct connection to the battery. This is a good start in the right direction but it misses an important point. Its not a good idea to connect any electrical circuit direct to the power source. Allways insert a fuse in the connection. Fortunately, most cars have a fuse box and most of those have a couple of spare circuits. Connect the inverter cables to one of the spares and insert the appropriate fuse. Check the instructions that come with the inverter. If there aren't any instructions, throw the inverter away and get a good one.
4. I'd suggest you look at something with at least 300 watts continuous, 600 watts peak. Also look for at least two outlets. These buggers do produce heat so ventilation is important. Make sure it has access to good ventilation. Also, check the supplied cables, some manufacturer's go cheap. Make sure they have a UL listing and are rated for the appropriate amperage, ie - 800 watts peak / 12 volts = 67 amps! That's a lot of current, it takes a big wire. You also want to look at what your car's electrical system can handle. That's one reason I went with the intermediate PowerStation, I just use the car to charge it when necessary.
There are lots of good inverters out there. Mine is a Coleman 300P, I think. Anyway, its a Coleman. I got it online through some sort of RV/truck accessories outlet for $60 including shipping.

I DEFINITELY would NOT hook it up to the fuse box!! I've repaired many car's electrical systems damaged because people hooked up amplifiers and other large current loads to the fuse box. Not a Good idea At All.

Go with the Direct Battery Connection. The Hardest Part is finding/Making a hole in the firewall for the power cable to go through. MAKE SURE you put an in-line fuse within 18" from the battery and make sure it is before where the wire go's through the firewall.

You can buy HIGH CURRENT quick connect terminals for amplifiers that would work with the Inverter. This would allow you to quickly diconnect and reconnect the inverter AND give you an easy way to hook up other 12 volt high current devices. MAKE SURE the terminals can handle at least TWICE the expected current demands and remember every device made today is not 100% efficient so factor it into your purchase and electical system design.

Cigarette lighter outlets are usually 10 amps Max. Good for cell phones and small loads, but not an Inverter. An Inverter is essentially an amplifier that outputs 120Vrms continous with varying current output so it must have the same or greater electrical connection to the car as a high power amplifier.

I would not advise using less than a 10 Gauge cable for the power connection. They probably supply 12 gauge cable with alligator clamps but this is NOT ideal.

With 12 volt systems, ANY resistance in the power line matters. And any resistance in the power line creates heat which is obviously not good. The more current your drawing the more heat that will be created by the small parasitic resistances.

Make sure the ground connection is good and solid. A Lot of people make the mistake of making the +12V line solid but totally forget the ground connections. Make sure the ground location is BARE metal. take the paint off the ground location and spray it with silicone or coat it with vaseline to prevent corrosion and rust.

If you dont think you can do a good job at it, take it to a car audio installation place and they probably will do it for 20-30 bucks. The installation quality will effect the performance and life of the inverter and maximise safety which is often neglected to save 3 dollars.