I have a 86 that did not have a front auxiliary fan. I,very scrounge one off a 87 to use. I don't gave a relay to plug the harness into. My question can I splice into the harness for the main fan to come on at the same time or install a relay with a manual switch? Wiring is not fortay so please keep things simple for me. Thanks in advance.

 

I ran a hot from the battery to another relay. Ground from frame to relay. Then tapped into the ground that turns on the relay to the new relay.. Look at the FSM for wiring on the relays.

 

You'll discover when it comes to automotive wiring, of all vehicle brands, they figured up the exact millimeter of distance needed between point A & B for the routing planned. Then calculated the voltage drop for that exact distance of DC wiring. Then figured up that circuit's load to the closest milliamp. Then decided to use whatever size wire gauge would just barely carry that load without melting down and said "Send it!"

Anyone that has ever done any wiring for long enough will tell you, man if only they had used 1 more inch, or if only it was 1 gauge thicker.... Well when you think about how many feet of wiring there is in just 1 car, an extra inch on every end of every connection adds up to many, many feet. And a thicker gauge of wire costs and weighs more. Then multiply that by thousands of cars and you have a massive increase in production costs, and a slight bump in weight.

That's why any time you want to add to a vehicle's power demands you really should be adding a supplemental fuse/relay box first. The main cooling fan circuit is just big enough to run only the main cooling fan. You REALLY should be using a relay to add a secondary fan. Plus the relay will allow you to have the primary fan circuit trigger your add on fan, vs using just a fused circuit and a toggle switch.

Once you understand relays and how to wire them you'll be wanting to use them everywhere. You've been warned
You can use the + or - to trigger the relay based off personal preference or how it's being tied in to other components.

On my truck and the Vette I have a relay off the ignition accessory that triggers other relays, so all the cascading add on stuff won't have power unless the engine is running, to save the batteries if i forget to turn off a toggle switch, but also so I don't have 10 wires jumped off the same ignition wire going to individual relays/circuits.

Spend about 20 minutes reading up on relays and how to wire them and then 40 seconds glancing over massive lists of their possible uses until you understand how simple they are to use and you'll be good for life.


To wire up a relay you'll need 4 wires,

• 12v + supply line (must be large enough for the load) it also supplies power to the relay for the electromagnet to engage the circuit contacts inside
• a ground wire (needed for the other half of engaging the electromagnet)
• a 12v + wire for the trigger, (unless you are using the ground as the trigger)
• then the + wire going out to the load

The trigger wire can be a much smaller wire. I've read of some people using CAT5 wire when using a bank of switches to relays but that seems way too small for my liking


If you are wanting to stay super simple just a fuse near the battery and a toggle switch will work, but the toggle must be rated for the amp load of the circuit