You may not have ever had a problem with wiring new lights into existing circuits, but it can happen. And as Murphy would tell you, it'll happen at the very worst moment.
A few years ago, I wired a new set of driving lights (with switch) in parallel with the high beams on my Grand Cherokee. They seemed to work great, but I could only try them for short stretches of time because of heavy traffic where I live. A couple weeks later I headed out to go hunting up near Gunnison Colorado, which for me means a trip over +11,000' Monarch pass. I got a late start, so it was about 10pm when I started down the back side of the pass, fully loaded with gear and towing a travel trailer. It was a cloudy, moonless night and there was very little traffic so I figured it was time to try out the new lights. They were great! It seemed like I could see for miles, that is until I was going around a sharp bend (the only kind of bend on Monarch pass) and the headlight fuse finally had enough. Bam! No lights at all and I'm in the middle of a corner going about 45 mph with a several thousand foot drop off to my left. Not much fun. I had to drive from memory, because it was pitch black. I somehow got stopped, got out my flashlight and found that I was on the shoulder of the oncoming lane, a foot or two from the drop-off. Using the flashlight, I got over to the other shoulder, turned off the driving light switch, changed the fuse (and my pants!) and drove the rest of the way at about 30 mph, shaking like a leaf. Needless to say, I put in a relay as soon as I got back!<img src=/images/forums/snitz/eek.gif width=15 height=15 border=0>
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