Owners of other Toyota, Lexus and Scion vehicles such as the 4Runner, Avalon, 86, C-HR, Camry, Corolla, iM, Land Cruiser, Mirai, Prius, RAV4, Sequoia, Sienna, Tacoma, Tundra, Yaris, FR-S, xB,  xD, tC, xA, CT 200h, ES 250, ES 300, ES 330, ES 350, IS 250, IS 350, RX 300, GS 250, NX 300 and RX 350.

The Highlander is equipped with the relatively newer style of "low profile" mini blade electrical fuses.

A white plastic fuse puller tool is included on the underside of the engine bay fuse box cover. Or you could use a pair of needle nose pliers with rubber insulated handles.

The mostly square shaped engine bay electrical box is located just behind the 12V automotive battery, in front of the brake fluid reservoir and to the right of the engine air filter box.

Gently push in the release tab on the front edge of the fuse box before lifting up the cover.

Turn over the fuse box cover to access the white plastic fuse puller tool.

There is a fuse location diagram on the underside of the fuse box cover and also another one in the owner's manual.

Push in the release tab on the front edge of the cover before pulling it straight off.

The interior passenger compartment electrical panel is located under the driver side of the dashboard.

Look under the dashboard behind the emergency / parking brake foot lever to locate the white plastic cover on the interior fuse block.

If you have trouble removing the cover, use a flathead screwdriver to carefully pry it off.

There is a fuse location diagram on the outside of the cover and also another one in the owner's manual.

Pull the old fuse straight out of the socket.

If the thin metal bar or "band" in the translucent plastic center of the of old fuse appears to be burnt or broken, it is most likely "blown" and should be replaced with a new fuse.

Push a new low profile mini blade fuse of the same amperage rating (e.g. 5A, 10A, 15A, 20A, etc) straight into the socket.

If the thin metal strip in the middle of the old fuse appears to be intact, the old fuse is most likely still good. Although since fuses are so inexpensive, it should still be replaced as part of your electrical issue troubleshooting process.

Replace the fuse puller tool on the underside of the cover for the main engine bay fuse box.

Push on the cover to secure the retaining clips.

If you suspect a faulty relay is your problem, the easiest way to test the theory is to simply replace the relay with a new one.

You could also test the old relay with a multimeter tool.

Lower the relay box cover back into place and push on it to secure the retaining clip.

Test the electrical component that you were having a problem with such as the horn, radio, power windows, wiper blades, interior lights, headlights, tail lights, power driver's seat, gauges, etc.

If you are still having the same problem, there may be a shorted wire somewhere or the electrical component itself needs to be replaced.

Be sure to record the fuse or relay change in your vehicle's service records.

Please check out all of my 2014-2018 Toyota Highlander DIY Repair & Maintenance Guides.