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Additional Fusebox
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One thing that I dislike about the Miata is the lack of 12V power access from the engine bay. Since the battery is in the trunk, the only way to access pure 12V power is tapping other equipment which may lead to blown fuse. Since I dislike risking OEM wiring and equipment, I finally address this problem by tapping the battery for pure 12V power.
NOTE: Others has tapped the 100A main fuse in the fusebox with good results. I didn't go this way because I did not want to risk the main fuse even if it'll take a lot to blow it.
First thing I did was locate the 12V battery cable coming from the trunk. The easiest tap is to connect to the 10g power cable coming out of the alternator. The red arrow shows the battery cable while the green arrow shows my NEW 12V lead.
1) Disconnect the negative power cable on the battery.
2) Locate the alternator and you'll be able to see the battery cable connected to it.
3) Uncap the plastic to access the nut, unbolt the nut. Don't worry about removing the cable, you don't need to remove it.
4) Make a nice long 8g wire with a loop cap big enough for the alternator bolt.
5) Loop the ends onto the bolt and put the nut back on.
6) Now, cut some of the plastic off the cap some that it can go over the additional wiring that you just placed on it.
7) Use some wire protector and secure your wire, and run it to the side fender area near the main fusebox.
8) I got a fusebox from Pep-Boys that was just the right size with a nice snap-cap cover. I fabricated a mounting bracket that holds it in place using a OEM bolt right under it.
9) Connect your new 12V lead to one side of the box (Note: I only used 3 of the leads)
Once it's done, you can now tap into pure 12V power without having to worry about blowing any fuse. On top of that, the box allows for protection by allowing easy access for changing out fuses.
My next project would be a waterproof casing to protect the whole unit. But as it now stands, it's semi-waterproof.
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Additional Notes: 04/13/2005
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This is something that happened today during a rewiring job I had to get done under the hood. Since I was pulling power from the above 'fusebox' mod, I essentially had a 'live' 12-volt power wire that is not grounded coming out of that fusebox.
I made a mental note to myself that I would need to pull the 25amp fuse from the fusebox everytime I work on the wiring since I don't want to give myself a 12-volt jolt by accident. Well, as it would have it... I forgot to remove the fuse during this last rewiring job and the power wire came in contact with the body of the car.
Since the body is grounded... the power wire arch a nice electrical charge of the main wire. Luck for me, I was not grounded to the car so I walked away from it. Also lucky for me was that I put a inline 15amp fuse between the wire and the fusebox. So when the contact happened... the charged blew the 15amp fuse and didn't make it's way back to the fusebox, which could have caused damage to the alternator for which it was drawing power from..
Point here is... use a low-ampage fuse whenever possible to protect your car's main electrical items, and also the item you are installing, i.e... amps, radio, foglights, etc. Also, never use mental note... you are bound to forget it on your next job.
