Originally Posted by cbowles
One is for the headlights. I have the H4 headlights, but want to rewire the lights to include relays and fuses in the lines. I have heard that it makes the lights brighter and I am all for brighter.
Are your bulbs rated at higher amps that the stock? Or are you changing the bulbs as well? If neither, then relays and fuses won't help.
A fuse limits the amps that can flow through it. Increase the amps beyond the fuse limit and you'll blow the fuse. The reason is to protect the wiring. If you get a short with an oversized fuse, you will likely burn the wiring and possibly start you jeep on fire before the fuse will blow. In-line fuses will NOT make your bulbs brighter.
A relay is just a switch that is turned on by a low amp signal. It has a certain rated capacity similiar to a fuse but that is to protect the relay.
On the headlights, save yourself some time and effort and don't bother, all you'll really accomplish is making your troubleshooting tougher if it breaks.
BTW: I didn't stay in a Holiday Inn Express last night, but I do work for an electrical engineering firm.
As for the fog lights, I would put in a fuse immediately. You can splice one into the 12v+ side of the lights and you're good to go. I would also put relay in as well. This is a little more complicate but not bad. Just remember that you'll splice into you're 12v+ fog again. The other two leads will be 12v+ from the switch and ground. You'll have to view the diagram of your relay to get the pinout straight.
The one on this page seems fairly straight-forward