Want to install a 12V relay for a transmission cooler fan.

I bought all the stuff, and plan to install my transmission cooler at my next oil change. I'd like to mount a relay for the fan somewhere near the fan itself, and run a multi-conductor wire into the cab that will connect the oil pressure sender and the fan relay to a unit inside the cab. Can anyone advise the best place to tap a keyed 12 volt supply good for around 10 amps close to the radiator? I'd hate to reinvent the wheel if someone has already done this.

 

@caribe makaira is the wiring guru

 

Toyota didn't give you any extra room to add 10 amps to an exiting circuit.
You need to use a relay and go from the battery. The battery is right there anyways.

 

Yep, I would tap off an ignition based source to trigger a relay that connects your fan directly to the battery.
EDIT: And have fuses.

 

That's what I was afraid of. I wanted a keyed supply, but I suppose that may be more trouble than it's worth. I'll probably wind up pulling a low-amp keyed feed for the relay coil. I just figured that someone smarter and more experienced than I had a more elegant solution.

 

On an older vehicle with much simpler electronics you may have gotten away with doing the simpler solution. But with your 3rd gen, I wouldn't chance it with all the computers and circuits talking to each other.

 

Excellent point.

 

I purchased a fuse distribution block and a relay block. Mounted neatly between the battery and firewall. You can bundle relay control through the already existing grommeted cab / engine compartment. Once complete you can use open switch spaces or mount an new switch panel. There are also monitoring devices that use the port. Then switch on the fan when temperatures indicate

 

Do you have some pics and links to what you used?

 

Battery cable

Battery Cables - iGreely 6 Gauge Battery Power Inverter Cables with 5/16'' Lugs for Solar Panle Automotive Motorcycle RV & Marine Made with Tinned Copper 1 Black & 1 Red 6AWG 2ft/60cm

https://www.amazon.com/dp/B09BZ7179X?ref=ppx_yo2ov_dt_b_product_details

Switching module
https://www.amazon.com/dp/B07V9M7FMH?ref=ppx_yo2ov_dt_b_product_details


Power distribution from battery

$16 RECOIL BBPG4 Bus Bar Positive and Negative 4 x 5/16” Studs and 4 x #8 Screw Terminals Power Distribution Block Busbar with Ring Terminals 250 Amp Rating

https://www.amazon.com/dp/B08RRYD6J3?ref=ppx_yo2ov_dt_b_product_details

Shrink tubing.

$8 400 Pcs Wire Heat Shrink Tubing Kit With Adhesive lined, Industrial Heat-Shrink Tubing for Wires, 3:1 Marine Grade Heat Shrink Wrap, Premium Large Electrical Waterproof Heat Shrink Tape-Black by DHOOZ

https://www.amazon.com/dp/B0BLK98LBM?ref=ppx_yo2ov_dt_b_product_details
No pictures truck isn’t here

 

OK, I'll ask the $64,000 question. Why are you adding a fan in conjunction with a transmission fluid finned cooler? I ran a 20,000 lb. cooler at the very front of the vehicle towing a 6,500 lb. trailer with no cooling problems. What makes you think you actually need an additional fan to circulate air through the cooler? What do you plan on using to monitor the ATF temperature?

What I'm saying is you may be doing more work than is necessary.

If/when I get back into towing, I may install something like this:

Fluid Control Thermostats (derale.com)

Currently I have uninstalled my cooler.

 

As mentioned already, I’d also use the battery to power a 10amp accessory, and this is what I did- I installed fans like these shown below to cool my AC condenser, especially when 4-wheeling or stuck in traffic in hot weather:

$36 12" Radiator Cooling Fan, 12" Radiator Cooling Fan Universal Slim Fan Push Pull Electric Radiator +12v 80W Mount Kit

https://www.amazon.com/dp/B0C9BY9G4G

And used this gang panel switch to manually control it along with other lights and accessories:

$97 6 Gang Switch Panel, Niwaker Automatic Dimmable Switch Box Universal Electronic Relay System Circuit Control Box Car Switch Panel LED Touch Control Panel Box for Truck Off Road SUV UTV Pickup Boat

https://www.amazon.com/dp/B088TG9W2M?ref=ppx_pop_mob_ap_share

The switch panel is mounted above my dash and has a control box I mounted
on the fire wall. Even though the box has built in relays, I just used those to control other relays mounted near the fans and other accessories like my ditch lights by using small gauge wire and fed them to power the relay coils instead of having to put heavy gauge wires through the fire wall.

 

In line fuse
https://www.amazon.com/gp/r.html?C=B6EM7Z6TLG8N&K=3AF5IPXQ5I85B&M=urn%3Artn%3Amsg%3A20240802220944a4465aff62d94429ac2329e5da80p0na&R=F61SS5GXVA5I&T=C&U=https%3A%2F%2Fwww.amazon.com%2Fgp%2Fproduct%2FB07426WCLM%2F%3Fref_%3Dpe_101622500_995673470_AG0400IMG_2p_0_lm&H=BYOE1QVIYUAAPTDDZDS8JUK1H7AA



switches
Nilight 50044R 5 Pack Waterproof 40/30 AMP Heavy Duty 12 AWG Tinned Copper Wires 5-PIN SPDT Bosch Style 12V Automotive Relay and Harness Set,2 Year Warranty

 

I kept heavy gauge wiring in the engine bay also and only sent control wires through the firewall

 

Yes, that was my plan as well. Thank you all for the links and feedback.

 

I guess that's a legit question. I don't know that I NEED it, but I do occasionally have cause to haul a trailer over the Divide, and I don't want to toast my transmission. It's already running ~180 - 200 degrees on a hot day with no trailer.