Wiring | What items need relays?

[Padawan]

All,
I’m using the American Auto 20 Universal wiring kit (wanted longer wires along with more electrical flexibility long term)...

Fuse Box is mounted, driver side top of foot box,
and I have a good idea on where all the wires are supposed to be ran...

I understand how electromagnetic switches work...

My question parts need relays?

Highlights - I assume
Fan - I assume
Turn Signals - I assume
Air Conditioner - I assume
Fuel Pump - I assume


Then I get a little lost on what else need relays?
Brake Lights?
Radio?
USB charging ports?
Heated Seats?
Fuel Sending Unit?
Should I been setting up relays for everything...??

To make things more complicated... I’m installing a self canceling turn sign module: Signal Dynamics 01017 Turn Signal Assemblies & Lenses

I was thinking some relays like this... it’s the #1 best seller of the 5 pin relay...although I don’t think I’ll need the 5pin relays:

https://www.google.com/aclk?sa=L&ai=DChcSEwj82u2EoazuAhXQwMAKHRQHDs8YABAEGgJpbQ&ae=2&sig=AOD64_0jiGYXUg5GOVjLAx8mKHXz8Ar4ag&ctype=5&q=&ved=2ahUKEwi-iuSEoazuAhVDmK0KHUxrB_EQwg96BAgDEBg&dct=1&adurl=

Are you creating a relay board behind the dash? Or where are you mounting the relays?

[frankeeski]

Headlight high/low beam 5 pin relay
Horn 4 or 5 pin relay
Fuel pump 4 or 5 pin relay
Engine cooling fan 4 or 5 pin relay (I prefer a 50 amp relay for this)

A/C system will come with what ever electrical wiring and relays it needs.
Seat heaters come with their own relays.

None of the other stuff you listed need relays.
I prefer to use 30/40 amp 5 pin relays for most stuff.

[Padawan]

Headlight high/low beam 5 pin relay
Horn 4 or 5 pin relay
Fuel pump 4 or 5 pin relay
Engine cooling fan 4 or 5 pin relay (I prefer a 50 amp relay for this)

A/C system will come with what ever electrical wiring and relays it needs.
Seat heaters come with their own relays.

None of the other stuff you listed need relays.
I prefer to use 30/40 amp 5 pin relays for most stuff.

Two questions:
1) Do I go with the hot wire from the fuse box, cut the hot wire running from the fuse box, wire the hot into Pin 30 of the relay, then take the remaining wire and run it from Pin 87 to the headlight?
86 goes to the switch and 85 would be chassis ground?
I would like to keep all the relays behind the dash if possible?

2) I just don’t know where to cut the wire off of the fuse box to wire in the relays and if I need extra fuses from the relays? —- it doesn’t feel like I need extra fuses in the line because I’m running them from the fuse box initially

Side question- if I used a relay connector switch — what AMP would it need to support - example terminal switch: https://www.lowes.com/pd/Utilitech-Quick-Wire-Connectors/999953938?cm_mmc=shp-_-c-_-prd-_-elc-_-google-_-lia-_-106-_-electricalaccessories-_-999953938-_-0&placeholder=null&ds_rl=1286981&ds_a_cid=112741100&gclid=EAIaIQobChMIg7u9nbWs7gIVRrGGCh1ILQp1EAQYASAB EgKVRfD_BwE&gclsrc=aw.ds

Thanks for all your help

[frankeeski]

For the headlights, there should be a headlight switch provision wired into the harness.
Out of the headlight switch to #30 on the relay, #30 jumper to #85.
Headlight low beams connect to #87a.
Headlight high beams connect to #87.
#86 connect to low/high toggle switch and other side of the low/high switch connects to a good ground.

Now if you using a Russ Thompson turn signal assembly and wanting to use the momentary switch on the end of the stalk to control low/high beams. Throw out everything I typed up above because you'll need a second relay (latching relay).

Don't cut anything until you're absolutely sure it needs to be cut. As far as those terminal strips go, I'm not a fan. Wired correctly, you shouldn't need to disconnect any of the electrical frequently. And I believe in eliminating as many points of failure as possible.

[Big Blocker]

What Frank said, to the letter. X2 on the latching relay or an electronic module if you want the RT stalk button to be your Hi-Lo switch.

There are multi-relay alternatives but require a minimum of four relays to work, five works better - this would not be my 1st choice as like Frank has mentioned, the more things in a circuit, the more there are places for something to go wrong (get loose).

Doc

[Bob Cowan]

A relay is an electrical switch, operated by another switch. Any circuit that has a power requirement higher than the switch you want to use needs a relay.

For example. The electric fuel pump will draw 25+ amps. It's controlled by the ECU, which can handle 0.5 amps. Obviously, you can't run the 25+ amp circuit through the ECU. So, you install a relay that will switch the high amp circuit on and off by the command of a low amp circuit.

Headlights are similar. You could install a 40 amp switch in the dash to control the headlights. But that's a big ugly switch, and requires large gauge wires under the dash.

Things like a radio and charging points are fairly low amperage, and they don't really need to be switched off and on as you drive. No need for relays there.

Relays are also nice when you want one small switch to control multiple circuits. Like door, hood, and trunk locks. Or top retract and ejector seat.