Have a MK4 complete kit. Used the Ron Francis wiring harness. The RF harness powers the cooling fan with an always hot fuse. How would one go about changing this to a keyed fuse?
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Have a MK4 complete kit. Used the Ron Francis wiring harness. The RF harness powers the cooling fan with an always hot fuse. How would one go about changing this to a keyed fuse?
Use a relay with ignition and the turn on input. It will act like a light switch for the fan. the 12 volts running to the fan will only be enabled if the key is in the ignition position. If you google for use a relay as a switch, you'll get tons of hits (e.g. https://www.electronicshub.org/what-...-how-it-works/).
MkII: 408 Dart block dry sump, 750cfm carb, G-Force T-5, 8.8 rear with 3.55 gears, 3-link, Kirkey seats, black ceramic coated twister mufflers with shields and adjustable turn down tips, passenger roll bar, front and rear roll bars. 2020 GT500 Magnetic metallic, with white and lime green stripes.
The Ron Francis harness powers the fan through a relay. The relay is ground triggered using either a thermostatc switch or EFI control. Some also use a manual override switch. The power to the relay is supposed to be from a switched source. If wired properly, the fan won't run with the key in the off position.
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Yes: "If wired properly, the fan won't run with the key in the off position"
I'm actually thinking about including a switch to either leave the fan on for a bit after ignition is off or turn the fan off when I want more than 190 degrees. LOL
Actually the RF harness designed to run the fans with the ignition off. Would like to know how to retire the the relay to a switched fuse. You can see in the diagram that it’s powered through the battery feed which means it always hot.
IMG_0542.jpg
This is how the RF fan circuit is set up:
The relay (pin 30) is always hot, but the blue fan +12v wire is only hot when the relay is energized by providing power to pin 86 and ground to pin 85, which closes the switch between pins 30 and 87.
Edit:
After looking at a picture of the RF fuse panel, it does actually look like the fan relay is getting BAT FED power on both pins 30 and 86 (via jumper wire). With EFI fan control, once the key is off, the ECU will open the fan control circuit. With a mechanical thermostatic switch, the fan will continue to run until the temperature goes below the switch's rated temperature. If you want to have the fan off with a thermostatic switch when the key is turned off, you just need to connect pin 86 of the relay to a switched power source like my diagram above shows.
This is representative of the picture above:
Last edited by Papa; 05-31-2023 at 09:17 PM.
My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754
(Most viewed Roadster build thread on this forum!)
Delivered: 6/17/2017
First Start: 12/30/2017
Completed: 12/7/2019
Legal: 1/30/2020
Member of the Mile-Hi Cobra Club
Dave's Cobra YouTube Channel: https://www.youtube.com/channel/UCbk...npK1UZHj4R-bYQ
Agora 1:8 Scale Cobra Build: https://thefactoryfiveforum.com/show...l-Build-Thread
Thanks for the help. I’ll try and contort myself under the dash tomorrow and fix it.
My Build Thread: http://thefactoryfiveforum.com/showt...ter-Build-9754
(Most viewed Roadster build thread on this forum!)
Delivered: 6/17/2017
First Start: 12/30/2017
Completed: 12/7/2019
Legal: 1/30/2020
Member of the Mile-Hi Cobra Club
Dave's Cobra YouTube Channel: https://www.youtube.com/channel/UCbk...npK1UZHj4R-bYQ
Agora 1:8 Scale Cobra Build: https://thefactoryfiveforum.com/show...l-Build-Thread
Gotter dun! Fifteen minutes and working like a charm. Thanks again.
The switched 12V is the assortment of BROWN WIRES. Connect the relay end of the cut red wire to the BROWN wires buss bar.
You should check that the BROWN wires is switched by the ignition switch first, just to be sure. This is what I did. This diagram shows how it is done (with a Sniper).
UNADJUSTEDNONRAW_thumb_128.jpg
Have fun,
Jeff
Mk4 Complete kit with IRS, IRS brakes, Power Steering, 302 mounts, 302 headers, TKO, 2 Rollbars, Leather seats,
vintage gauges, polished stainless sidepipes, front and rear sway bars, all cutouts.
Blueprint Engines 347 stroker; Tremec TKO 600; 3.55 IRS, 17" Bullitt wheels: 9" front 10.5" rear.
Delivered Nov. 6, 2018. First start Aug. 11, 2019. First Go-Cart Feb. 21, 2020.