How Automotive Relays Work (30, 85, 86, 87 Explained Clearly)

Automotive relay wiring doesn’t have to be confusing. In this video, I show you exactly how automotive relays work and what terminals 30, 85, 86, 87, and 87a actually do in real circuits. If you’ve ever looked at a relay diagram and felt stuck, this will fix that. In this lesson you’ll learn: • What a relay really does inside • How the control side (85 & 86) works • How the switch side (30, 87, 87a) carries load current • How to wire a relay correctly • Common mistakes that blow fuses or cause no-start issues • How relays show up in real vehicle circuits This is foundational electrical knowledge every technician and DIYer should understand. WATCH THIS NEXT: How to Read Automotive Wiring Schematics for Beginners    • How to Read Automotive Wiring Schematics f...   TOOLS USED FOR DIAGNOSING ELECTRICAL ISSUES: Test Light (simple and reliable circuit testing) https://amzn.to/47CMjQ7 Digital Multimeter for voltage drop and circuit testing https://amzn.to/4tDNhoG Automotive Jumper Wire Kit https://amzn.to/4ru9u7n Power Probe (quick power and ground testing) https://amzn.to/4kJohbA Professional Scan Tool https://amzn.to/474bw5I ELECTRICAL DIAGNOSTIC TOOLS I RECOMMEND: Back Probe Kit (test connectors without damage) https://amzn.to/3P2NmCD Terminal Removal Tool Kit https://amzn.to/4uruoG8 Heat Shrink Connector Kit https://amzn.to/40IsPpH Fuse Assortment Kit https://amzn.to/4cBxvEV Wire Stripper / Crimper https://amzn.to/3Nh32BI Battery Tester https://amzn.to/47d7E2H OBD2 Scanner (budget scan tool for DIY diagnostics) https://amzn.to/3NaCbaw MY DEVOTIONAL FOR TECHNICIANS: Toolbox Truths: A 365-Day Devotional Guide for Automotive Technicians & Tradesmen Written specifically for mechanics and serious tradesmen. https://amzn.to/4qUxmQc Affiliate Disclosure As an Amazon Associate I earn from qualifying purchases. Chapters: 0:00 Introduction 0:45 What is a relay? 2:10 Terminal numbering (30/85/86/87/87a) 4:00 Wiring example 6:30 Common mistakes 8:00 Practical applications