Hey. I am going to be wiring up a set of fog lights for my '01 XLT and was wondering what pin on a pair of Sylvania Silverstar 9145 bulbs is positive? I plan on making this OEM-esque. I bought the wiring connector for the bulbs, but my truck isn't wired from the factory for fogs so I can't do the eyeball comparison to see how it's wired. There are two wires going into the connector; one is (I assume) power and the other is ground (again, I assume so). The bulbs and connector are keyed, of course, so which pin is power and which is ground?

 

On a 2 pin bulb, it really doesn't matter,
If both wires are Black, pick either the left or right pin and make it ground, do the same for both lights.
If 1 wire black and 1 wire colored, use the black wire for ground.

 

Well, I like that answer. Easy peasy. But, if I can ask for more knowledge, why exactly doesn't it matter? The connector has two black wires, so why can either be power? I don't question your knowledge, but don't want to waste money either by burning a bulb or worse.

 

A light bulb is a resistor wire that heats up when voltage is applied, this "resistor wire" is called a Filament when inside a light bulb

The Sylvania Silverstar 9145 uses a tungsten filament in a glass vial with vacuum with some halogen gas inside, the halogen helps make the tungsten wire last longer

So its just a wire inside a glass vial/bulb, no + side, no - side, because its just a wire

If you place 12volt on one end and 12v on the other end what will happen..................nothing, there is no flow of electricity, so tungsten wire can't heat up
So you need 12v on one end and 0volt, negative, on the other end, electricity flows and wire heats up
Which end is 12v and which end is 0v doesn't matter to the tungsten wire

LED bulbs can be different, some of these do have a small circuit board with the bulb, and do have a + and - but it will be clearly labelled

 

Awesome. I'm tracking. This makes wiring up my fogs that much easier.

Thanks you two.

 

Quick question: is it better to physically ground one end of the bulb, or connect it to the negative battery terminal? I've read both in my research. My understanding is that it's the same thing. I was going to just ground it by connecting to bare metal on the chassis.

 

Yes, bare metal, attach it then paint over it so it doesn't rust

Most body parts are grounded, but not all are "good" grounds

vehicle parts are painted FIRST then assembled at the factory, and they are held together by metal nuts and bolts but using rubber washers, so...............not all are good grounds

Frame is a good ground, because tail lights have to use it as their ground
Radiator support is a good ground because head lights use it
Firewall on cab is a good ground because cab electrics use it
Engine is a good ground because starter motor and alternator use it

All the above should have a ground wire/strap connected to battery negative either directly or via a jumper wire to a direct wire

 

Good stuff. Thanks.