What relays are necessary with an aftermarket harness?

[Mopdog]

I have purchased and am preparing to install an American Autowire Power Plus 20 harness into my carbureted 1973 SBC Swapped 40. The current condition of my harness is bad beyond description. Somehow it ran occasionally and a few things worked intermittently. I’ve thoroughly read the install instructions and completely gone through the existing harness to familiarize myself with the undertaking. The harness directions only call for relays on the horn and electric cooling fan if applicable. Should I run one for the front heater blower as well? Is there anything else that should have one? Thanks for any feedback.

 

[B y r o n]

Usually you want to run relays on high amp draw items; headlights, driving lights, fog lights, electronic fans, electronic fuel pumps, etc.

 

[fjwagon]

That's great question but not easy to answer. As Byron suggested. It mostly had to do with high current but there are a lot of other reasons like if you want keep the same gauge wire to energize a relay....and then on the load side go with a larger gauge wire which the circuit may be required. Another reason could be to keep a shorter path from the battery to the load. This also helps from getting a voltage drop a smaller gauge wire and effect the output. You control several circuits at the same time. You can simultaneously turn off part of circuit and turn on another. Even low amperage circuit have circuit. The relay can be a normally open or normally close or both. So relays are really if you use them correctly.

 

[fjwagon]

I would use the oem manual and see if you see a relay in the schematic. If so i would use one. Also just All circuits that have a load should definitely have fuse.

 

[ToyotaMatt]

 

[Mopdog]

All circuits in the kit are fused. I’m waiting on a reply from their support people. I’m curious what they have to say.

 

[pb4ugo]

I would add relays for the headlights by using Toyota's stand alone harness & kit 81110-60p70, or some other vendor's kit.

 

[rickpaw]

Agreed with what Byron suggested. Also I'd add relay for the starter solenoid as well. Takes the load off the ignition switch. I'd get one of those relay blocks on Amazon to keep every thing together