I'm installing new electric cooling fans but can't use the factory e-fan controls because I'll be pulling up to 60amps with three 10" fans, the PCM switch can't handle that much nor can the power supply line which is only rated for 20amps. I'm installing a beefier harness and relay. However, I need to make sure the fans are only running when the ignition is turned on. I'd rather not go through the added hassle of fishing through the firewall to the dash fuse box to locate a switched 12vdc circuit. Does anyone know where I can locate a 12vdc switched circuit under the hood?
Thank you in advance for your help.
Oops... This is a 1991 Cherokee Sport, 4.0L. I'm installing a new all aluminum 2 row radiator due to catastrophic damage to the perfectly good all aluminum 3 row previously installed and cooled by the OEM mechanical fan and aftermarket e-fan until the fan bolts vibrated loose and the fan flew into the radiator. I had planned to upgrade to all electric cooling anyway... I now have 100% coverage on the shroud so all air being moved by fans will come through radiator.

 

Dunno if it's the same for a 91, but I have a diagram for the PDC on a 93. Any of those relays except the starter relay should have an ignition on signal to the relay, I think.

But don't just go by a diagram. That's what meters are for!

You'll be using relays to power your fans, correct?

As long as you are using the input from an ignition on signal somewhere in the PDC to trigger a relay, you should be good. Standard automotive relays only draw about a quarter amp across the coil, so no worries about loading The ASD relay output should be a good choice. It powers quite a few things when the key is on.




1993 PDC relay locations

 

There weren't many changes between 91 and 93, my PDC looks just like that, it might have one extra relay for the ABS which I don't have. I'm new at the electrical methodology of the automotive world, new information is easy to understand but I need to see it. I'll need to look at a schematic to figure out which wire or pin I'm tieing into unless you can tell me. You mentioned attaching to the load of the ASD relay...
I'm assuming that none of these relays have a signal leg tied to the ignition to tell it that the ignition is on or off, the PCM takes care of that (?) and sends power to the entire PDC when the ignition is turned on (?). I'll need to "google" a schematic to see which of the relay legs I'm attaching to. This is going to be fun. I'll keep an eye on this thread, if you respond back with a leg number on the ASD or Cooling Fan relay that I can use that would be awesome! Thanks so much for the info.
I'm still learning the mechanical side of this Jeep (my other cars are too new to work on myself, one is a Duramax Diesel) so I'm taking it very slow with the under hood electronics.

 

I found this out there among many others. This seems to point out that there is a common ignition switch connection running along the buss bar of the fuses. I have not tested it with my meter to see voltage and when it's on/off but I figure if I connect to the opposite side of the buss bar and use a 5amp fuse to make the connection I'll be safe in one of the unused spots. I also included a picture of my PDC, it's a bit different than the 1993 diagram that you sent me and it's also different than this 1991 diagram. Jeeps are sure fun puzzles to figure out aren't they? Especially when you've bought a used one that's been bastardized by multiple hacks already. lol




Off topic... but what is "Alternate Power 1" and "Alternate Power 2" used for?

 

There should be. Find out if it goes on with the key, and there you go. Use that to fire a relay and you'll be good to go. A one amp fuse would be good coming off that buss bar.

www.the12volt.com is a great resource for all things automotive electrical, particularly using relays to do tricky things.

Or fire your questions here and we'll get you sorted out.



I have no clue!