FSS temp switch
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Senior User
Joined: Sep 2008
Posts: 318
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From: Portage Des Sioux, Mo
FSS temp switch
I searched but could not find this answer. My temp switch for the FSS broke a blade off. When I check autozone or NAPA the switch they show does not look anything like the 1 that is broke. The broke 1 has 2 flat blades. The 1 at the store has 2 pins and needs a connector. Does anybody know if this is a replacement and I need to change the connector to use it.
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Postmaster
Joined: Aug 2010
Posts: 2,554
Likes: 7
From: Northern Arizona
That unit is the Cold Start Thermal Switch... it activates the high idle solenoid. It is a Ford dealer item only.
Ford Part number: E8TZ-9E939-A
I think it costs about $50, and the general consensus is that it is not necessary and does not help your truck start any easier. It just kicks the idle up until your coolant is ~100 degrees or so. Most folks just leave it unhooked if it fails. Mine shorted out and burned up the fusible link that supplies power to the FSS. I just replaced the burnt link and left the wire off the CSTS and have not missed it. Hope this helps.
Ford Part number: E8TZ-9E939-A
I think it costs about $50, and the general consensus is that it is not necessary and does not help your truck start any easier. It just kicks the idle up until your coolant is ~100 degrees or so. Most folks just leave it unhooked if it fails. Mine shorted out and burned up the fusible link that supplies power to the FSS. I just replaced the burnt link and left the wire off the CSTS and have not missed it. Hope this helps.
Elder User
Joined: Feb 2012
Posts: 888
Likes: 2
That unit is the Cold Start Thermal Switch... it activates the high idle solenoid. It is a Ford dealer item only.
Ford Part number: E8TZ-9E939-A
I think it costs about $50, and the general consensus is that it is not necessary and does not help your truck start any easier. It just kicks the idle up until your coolant is ~100 degrees or so. Most folks just leave it unhooked if it fails. Mine shorted out and burned up the fusible link that supplies power to the FSS. I just replaced the burnt link and left the wire off the CSTS and have not missed it. Hope this helps.
Ford Part number: E8TZ-9E939-A
I think it costs about $50, and the general consensus is that it is not necessary and does not help your truck start any easier. It just kicks the idle up until your coolant is ~100 degrees or so. Most folks just leave it unhooked if it fails. Mine shorted out and burned up the fusible link that supplies power to the FSS. I just replaced the burnt link and left the wire off the CSTS and have not missed it. Hope this helps.
Logistics Pro
Joined: Sep 2010
Posts: 4,411
Likes: 4
From: Victor, MT
Here ya be:
The Switch to turn it on:
The wire running through the firewall:
The hole that I ran the wire through:
The wire just runs across the engine bay to the Fast idle Switch:
Hooked it up to the fast idle switch, btw, there is a barb in the middle of the spade, i used my sheet metal clamps to flatten it and stuck a spade connector on there:
Thats what I did.
The Switch to turn it on:
The wire running through the firewall:
The hole that I ran the wire through:
The wire just runs across the engine bay to the Fast idle Switch:
Hooked it up to the fast idle switch, btw, there is a barb in the middle of the spade, i used my sheet metal clamps to flatten it and stuck a spade connector on there:
Thats what I did.
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Senior User
Joined: Sep 2008
Posts: 318
Likes: 1
From: Portage Des Sioux, Mo
Might just let it go till winter and see what happens. I have issues about not hooking things back up they way they are supposed to be....... Unless it makes it go faster 
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Logistics Pro
Joined: Sep 2010
Posts: 4,411
Likes: 4
From: Victor, MT
The way ive done it, works just the same except your in control of it, its nice in the winter time when you start it...cause you can leave it on as long as you like, plus, if you ever have a extremely hard start, the fast idle switch i installed will start charging the batteries....
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Logistics Pro
Joined: Sep 2007
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From: Western Mass
The factory setup does control both cold timing advance and the fast idle solenoid. You can setup a manual switch a few different ways to control only the idle, or for both. I think the correct way to do a manual switch would be either two switches, or just the fast idle. There may be issues running the cold advance for long periods, where a fast idle might be beneficial for keeping the engine speed up for tasks like hydraulics or electric winches.
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