few questions about building my headlight harness...

so I've read all the threads I could find on and a few on some other sites but still have some questions, probably retarded ones since I'm no electrical guru :dunno:

I've read that regular relays can cause voltage spikes, so would it be worth the extra couple bucks to use resistor or diode protected relays? would it help extend the life of the bulb or would it be a total waste of money?

also I've heard the horror stories about cheap chinese blade fuses not popping when they should, so whats a good brand to look for?

and everyone seems to recommend rallylights.com, is that still the best place to get my supplies?

thanks fellas

Don't bother buying diode protected relays unless the price difference is less than a quarter. Just put the diodes on yourself - they go across the coil leads with the striped end toward the 12 volt power source, i.e. the end without the stripe goes toward ground. Buy a "rectifier assortment pack" at Radio Shack (will include 1N4001s through 1N4007s, all of them will work fine) or any rectifiers you can find with 50+ volt PIV rating and 1+ amp IF rating.

EDIT: what these are really there for is to shunt "back EMF" out - a relay coil is like an electronic flywheel. It stores energy in the form of a magnetic field, and resists change in current flow. So when you turn the relay off, suddenly there is no current flowing and the magnetic field collapses, producing a large voltage across the coil, which can make your switch contacts arc and wear out faster. Installing a diode in this configuration does not affect the circuit when you turn it on or keep it on, but allows the current to drop gradually and avoids an arc.

thanks for the explanation, that makes sense now... so in this application the diode isn't really necessary right? I would think running full amperage through the headlight switch would be more wear and tear on it than the spike from the relay, or am I totally wrong again lol

Running full amperage through the headlight switch is probably more wear and tear on it, but more importantly (headlight switches are a dime a dozen at the JY) will result in dimmer lights, as there is that extra wiring length between your lights and the battery. The diodes and relays are pretty easy to add, so it's well worth it - this is probably my next mod, I have a factory headlight wiring harness I'm probably going to tear apart for the harness connector since mine is pretty badly corroded and my driver side headlight connector is getting to the "oh, it doesn't work today, smack it and drive over a few potholes" point in its life.

EDIT - I'd still use the diode, they're really cheap to add and will preserve your headlight switch. When you make the connections to the relay coil just add the proper lead from the diode into the connection and insulate it properly and you're all done.

thanks again kastein, time to order parts