NAXJA Forums -::- North American XJ Association  

Go Back   NAXJA Forums -::- North American XJ Association > NAXJA Unibody Jeep Technical Forums > Jeep Cherokee XJ (1984 - 2001) > OEM Tech Discussion
HOME Member FAQ Sponsor Info Rules Bylaws E-Mail

OEM Tech Discussion Forum for OEM (Original Equipment) or stock XJs and MJs.

Reply
 
Thread Tools Display Modes
  #1  
Old May 15th, 2018, 22:33
obaa-xj obaa-xj is offline
NAXJA Forum User
 
Join Date: Dec 2008
Location: PNW
Posts: 99
'90 4.0 underhood switched power lead?

Hi,

Is there an ignition-switched +12 lead somewhere underhood on a '90 4.0?
I'm wiring in an aux cooling fan underhood, and looking for something I can use to trigger it on only when the ignition is on. I'd like to avoid trying to wire to the interior fuse box as the "empty grommets in the firewall are already stuffed with other wiring, plus it'll be much tidier this way.

Thanks!
Reply With Quote
  #2  
Old May 16th, 2018, 07:03
Saudade's Avatar
Saudade Saudade is offline
NAXJA Member
 
Join Date: May 2005
Location: SoCal
Posts: 2,039
Re: '90 4.0 underhood switched power lead?

+12 Key on is Yellow. Looks like the Ign module, O2 Heater realy, FP relay, and even the diagnostic connector have yellow supply wires.
__________________
1988 Laredo 2wd Auto, AKA "Grey Ghost", 200K
Reply With Quote
  #3  
Old May 16th, 2018, 09:00
RCP Phx RCP Phx is offline
NAXJA Forum User
 
Join Date: Mar 2003
Location: Phoenix,Az
Posts: 11,055
Re: '90 4.0 underhood switched power lead?

The best way to wire it will depend on what your doing with the fan?
Reply With Quote
  #4  
Old May 16th, 2018, 12:45
obaa-xj obaa-xj is offline
NAXJA Forum User
 
Join Date: Dec 2008
Location: PNW
Posts: 99
Re: '90 4.0 underhood switched power lead?

Thanks!

Is the +12 key plain yellow, or yellow with the black tracer? Generically, any (oem) yellow (or yellow/black?) wire under the hood should be +12 key? (Yes, I'll confirm myself with a meter..... I hate cutting through the insulation on a wire in order to tap into it, so I'm going to look for one with an exposed terminal which I can tap into.

As to background, the viscous coupling on my mech fan stopped coupling... I took it off, and my long term mileage records show there is an mpg improvement, and a (psychological, probably) seat of pants improvement. However, in the past couple of weeks, the temps shot up in the PDX area and it started overheating with only the aux AC fan.
I had a spare AC fine, so I wired in a 30A 5pin relay to power it. The current trigger is tapped off the existing AC fan, but that means the new fan doesn't kick in until the engine is already hot.
I want to do to things:
First, wire the trigger to +12 key, so it turns on when the Jeep is running. That should get me by for a while.
Second, I plan on adding a thermostat housing from a '96 that is tapped for a temp sensor switch. I saw a couple different sensors (for idiot light, not gauge).
If the sensor has a single lead, I'm guessing it will just short to gnd when triggered, so I will wire the gnd of the relay trigger circuit to it.
If the sensor has dual leads, I'm guessing it will contain a switch, but I will still wire the trigger gnd through it.
Reply With Quote
  #5  
Old May 16th, 2018, 16:22
four_shot's Avatar
four_shot four_shot is offline
How 'bout it Gonzo
 
Join Date: Jul 2003
Location: Waukegan, IL
Posts: 681
Re: '90 4.0 underhood switched power lead?

I'd recommend something like this:

https://www.amazon.com/dp/B00T4ANIH4...detail_0?psc=1

As long as it turns on around 200-210 and off at 185-190
__________________
....
4shot
"Babs" 97 sport 4.0 aw4
R.I.P."Buster" 86 laredo 2.8 ax5 10/85-9/17
In memory of Dave "Gonzo" Steele 1975-2008
Reply With Quote
  #6  
Old May 18th, 2018, 06:40
Saudade's Avatar
Saudade Saudade is offline
NAXJA Member
 
Join Date: May 2005
Location: SoCal
Posts: 2,039
Re: '90 4.0 underhood switched power lead?

The wire is just Yellow, no tracer. You can back probe through the connector to verify key on.
__________________
1988 Laredo 2wd Auto, AKA "Grey Ghost", 200K
Reply With Quote
Reply


Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
where is a good ign switched power source? Ben824 Modified Tech Discussion 4 May 3rd, 2012 11:48
switched from a pc to a mac Ba-Riedo Non-Tech / Off Topic 18 August 5th, 2010 13:56
Sources for switched power BIGSLVRXJ OEM Tech Discussion 8 August 10th, 2008 22:58
Good source underhood for switched 12v?? 1996cc Modified Tech Discussion 4 January 16th, 2007 23:37
94 underhood power center to 87 87manche Modified Tech Discussion 10 February 15th, 2006 19:28


All times are GMT -7. The time now is 03:01.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
NAXJA and NAXJA logo's Copyright NAXJA. All content/images Copyright NAXJA 1999-2014