when you need a 12V power wire for anything that you want to wire up in the car, say a vtec controller or a relay or a gauge or whatever, where should you get the 12V from? is it ok to jus splice into another wire that is supplying that 12V, or should you go directly to the positive terminal on the battery?

for example, say i spliced into the 12V wire going to a relay to power a new relay. would this affect the voltage or current going into the original relay? im trying to think of a circuit diagram, and it seems like it will be a parallel circuit where the voltage is the same...or i may be wrong.

 

Well I wouldn't splice into the cars power wires because the loads on these wire has already been determined by the manufacturer of the car. They don't design them for you to start adding things on. While it may work because they have designed in a saftey factor I wouldn't do it.

Since you plan to run a vtec controller ask yourself what happens if it dies. Or the line you attach it to dies. Something like this I would attach directly to the battery.

 

Check out these pigtail fuses:

http://www.tessco.com/products...Id=12

They have a wire soldered into one leg of the fuse. I've used these over the past few years when installing auxiliary equipment and cell phones.

 

sorry if this is a dumb question, but how exactly could i use the pigtail fuses?