What size fuse is used for the fog light circuit?

A 20-amp inline fuseholder is shown between the battery positive terminal and relay terminal 30.

Which Bosch relay terminal connects to the fog/driving lights?

Terminal 87 feeds the two fog/driving lights, which are wired in parallel and each grounded separately.

How is the relay triggered on and off?

Terminal 85 is connected through an SPST on/off toggle switch that gets power from the fusebox (IGN or battery power); terminal 86 is grounded.

Where does the switch get its power?

From the vehicle fusebox, labeled "IGN or Battery Power" in the diagram.

Is there an indicator light in this circuit?

Yes, an indicator lamp is wired into the switched circuit with its other side grounded, so it lights when the fog lights are switched on.

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Fog/Driving Light Relay Wiring Diagram - Bosch Relay, 20A Fuse, SPST Switch

Color wiring diagram for fog/driving lights with Bosch relay, SPST switch, indicator, and fuseholder

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Illustrated wiring diagram showing fog/driving lights wired through a Bosch relay, 20A fuseholder, SPST switch, and indicator from the battery.

AI caption February 2006 · Photo 130 of 364

This is a color wiring diagram (credited "Craig Ueltzen 1999") showing how to wire aftermarket fog or driving lights using a Bosch-style relay. Two fog/driving lamps are wired in parallel to relay terminal 87, with each lamp body grounded separately. The relay's terminal 30 receives battery power through a 20-amp inline fuseholder connected to the battery positive terminal; the battery negative goes to ground. Relay terminal 86 is grounded, and terminal 85 is the trigger, fed through an SPST on/off toggle switch that draws its power from the vehicle fusebox (labeled "IGN or Battery Power"). An indicator light, grounded on one side, is tied into the switched circuit so it illuminates when the lights are on. Terminal 87A is shown but unused. The diagram gives a reader the complete relay pinout usage (30 = fused battery feed, 85 = switched trigger, 86 = ground, 87 = load/lamps), the recommended 20A fuse rating, and grounding points for the lamps, relay, indicator, and switch circuit. It is a generic auxiliary lighting relay schematic rather than a vehicle-specific factory diagram, so it applies to nearly any 12V vehicle including the uploader's Jeep TJ.

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Frequently asked questions

What size fuse is used for the fog light circuit?: A 20-amp inline fuseholder is shown between the battery positive terminal and relay terminal 30.
Which Bosch relay terminal connects to the fog/driving lights?: Terminal 87 feeds the two fog/driving lights, which are wired in parallel and each grounded separately.
How is the relay triggered on and off?: Terminal 85 is connected through an SPST on/off toggle switch that gets power from the fusebox (IGN or battery power); terminal 86 is grounded.
Where does the switch get its power?: From the vehicle fusebox, labeled "IGN or Battery Power" in the diagram.
Is there an indicator light in this circuit?: Yes, an indicator lamp is wired into the switched circuit with its other side grounded, so it lights when the fog lights are switched on.