Budget Relays - Junkyard Builder

We found this relay board bolted to the inner fender of a late-’90s Nissan. Most domestic cars tie their relays into a large fuse box that can be difficult to reuse. This board incorporates five relays of different load capacities. If the relay is not marked with an amperage load, you can estimate its capacity by the size of the wires leading from the connector. The yard charged us just over $26 for this.

We found this relay board bolted to the inner fender of a late-’90s Nissan. Most domestic

Every car in the junkyard has value. It all comes down to paying attention to opportunities when they arise. Car Craft family member Tim Moore is a card-carrying JYB-er who keeps his eyes open and is even willing to cruise the import side of the yard looking for a choice component. During one of his many visits, he came upon a simple board containing five-ganged relays from a '90s Nissan.

Before we get into how to wire and apply these relays, it's probably best to review what relays do and how they work. A relay is designed to allow a light-duty switch to control a high-current draw load. A typical example would be a 30-amp relay used to control an electric fan. You could just wire the fan from the battery through a heavy-duty toggle switch on the dash using 10-gauge wire and take it back to the fan. Imagine five different loads all connected that way with a wrist-size gang of 10-gauge wires all running under the dash. That would be clumsy and unnecessary. Now imagine mounting a small, 40-amp relay alongside the fan and connecting a short lead of 10-gauge wire to a nearby 12-volt positive terminal. Ground the relay then run one small, 16-gauge lead from the relay to the switch and another to a switched ignition source. The heavy battery power and ground wires are very short, while the longer control wires are very small. We can now use a compact, light-duty switch to control our 30-amp fan through this relay and we've eliminated a long length of large wire that would likely produce a measurable voltage drop across the circuit. Instead, the relay delivers more power to the fan. This is exactly how late-model cars use a low-voltage computer signal to control high-load items like electric fuel pumps, cooling fans, and other electrical devices.

This is the connector side of a typical relay—we’ll use this orientation to call out the four main connectors. The Bosch relay is on the left, while the import version is on the right.

This is the connector side of a typical relay—we’ll use this orientation to call out the f

As another example, most '60s and '70s cars route the full headlight amperage draw through the headlight switch. After years of use, corrosion creates resistance in the switch connections causing the connector and wires to melt due to the heat. By placing relays near the headlights, you can increase the voltage so they burn much brighter. Other devices you can control with relays include trailer or driving lights, electric fans, electric water pumps, the high-current side of defrosters or A/C fans, and virtually any other switched electrical device. The junkyard relay board we found wasn't exactly cheap. Later we found an Internet source (Parts-Express.com) that will sell Bosch 40-amp relays with matching wiring sockets for $4.08. With shipping included, five new relays and connectors would cost $29.98. That's only $3.50 more than what the junkyard charged us for used relays, so be careful. Build your own aluminum custom mounting board and you're there.