Relay Race

M.A.D. Enterprises offers...        read full caption M.A.D. Enterprises offers a relay kit that consists of a 15-amp relay, a wiring harness, and a fusible link. We added an insulated terminal block that can be used as a connection from the relay.

We mounted both the relay...        read full caption We mounted both the relay and the terminal block on a small strip of aluminum that can then be mounted in a convenient place under the dash near the fuse block.

This is the wiring diagram...        read full caption This is the wiring diagram for the relay. Most relays of this design are wired the same way using the same numerical designations. Note that the 87a terminal is not used. The connection for 86 can be wired to any switched connection on the fuse block. Every other switched accessory can be connected to the large insulated terminal. M.A.D. also includes a handy instruction manual with its relay kit that offers several additional wiring ideas for using relays in different applications.

Chevy musclecars are great for modifying because there’s room to work and every system is very simple. But one distinctly insufficient area is electrical power taps under the dash. Chevy thoughtfully provided several extra switched and unswitched electrical power connections on the factory ’60s and ’70s fuse blocks. Unfortunately, often there aren’t enough connections to feed all those power-hungry accessories available today. Worse yet, the additional current draw of all these extra accessories creates additional heat in the fuse block that can cause a meltdown.

The solution is an idea promoted by our pal Mark Hamilton at M.A.D. Enterprises. He’s a believer in using relays for many kinds of electrical circuits. M.A.D. offers a universal relay kit that works perfectly for this application. The relay is fed by a 12-gauge power wire that is connected directly to the horn relay located near the radiator along with a fusible link.

This under-dash relay can then supply switched battery voltage separately from the fuse block. The power lead from the under-dash relay is connected to an insulated terminal stud that can supply up to 15 amps of current to electrical accessories. This setup is positioned under the dash where most of the electrical accessories are located. You can connect all your electrical power accessories such as the stereo head unit, tachometer, gauges, or other accessories. This both reduces the load on the fuse box and the ignition switch, and it also greatly reduces the clutter of wires snaking into the fuse box. How many times have you found the main battery feed-wire connection to the ignition switch melted due to excess heat?

The relay and terminal can be mounted on a small aluminum panel and located almost anywhere under the dash where there’s room. We’ve found the area just above the driver-side kick panel is close to the fuse block yet easily accessible. You could also add a second relay and terminal for switched power energized only when the headlights are turned on. Take a look at the photos and the wiring schematic and then look at the mess that currently infests your fuse box. You’ll know what to do.