Original text sourced from a forum discussion on upgrading the fog light wiring for a vehicle.
The original poster has stock fog lights on a 1998 XJ and plans to upgrade to more powerful bulbs (greater than 55W). They intend to upgrade all wiring and are inquiring about pre-made harness kits, referencing an eBay listing for a HID wiring harness. They express concern about the wire gauge (14 AWG) and relay rating (30A) in the kit, preferring 10 or 12 AWG wire and a 40A relay. They ask for instructions if no suitable pre-made kit exists.
A respondent advises that fog lamp kits typically include wires, a switch, and a relay, and nothing more complicated is needed. The recommendation is to use the stock fog lamp switch and wires to control a standard automotive relay in the engine compartment, using the relay output to power the new fog lamps.
The original poster seeks confirmation, asking if the wires from the switch to the new relay are sufficient and if power should be run directly from the battery through the relay.
Another user confirms this approach: use the existing wiring and switch to actuate the relay, and run the power for the lights from the battery with an appropriate fuse. This maintains original functionality, such as the fog lights turning off with high beams, and keeps the modification legal and simple.
A discussion ensues about relay pin configurations. One user points out a potential error in a diagram, suggesting both lights should be connected to the normally open pin (87) so they only activate with the switch. Another clarifies that if using a DPST (Double Pole Single Throw) relay, common in light harnesses, both output pins (87 and 87a) activate together, which would be correct for the described setup.
The original poster plans to use the relay supplied with new PIAA lights. Their goals are to ensure the fog lights only operate with low/parking lights and that the full electrical load does not pass through the switch. A suggestion is made to connect the relay's 12V control source to the low beam circuit to automatically cut fog lights with high beams. Another user notes that using the original switch and wiring for relay control already accomplishes this, allowing the power circuit to be independent. The original poster confirms this is their plan, aiming to be fully prepared before starting the project.
