Complex, yet probably simple electrical concern:

[Stewart G Griffin]

If we could look at this first diagram, this is how i was running my electric fan (a Spal by the way) for the past year or so with no problems whatsoever:



But today i said what the heck and wanted to install the 3 prong lighted switch i got last year with the fan, but ended up not using it because i had trouble getting it to work and thus went with the 2 prong toggle above.  Again,  that setup worked totally fine this past yr.

So, this is the setup i tried today:


After i got it all hooked up and tested----the fan and switch light worked fine, i then buttoned everything up.  To do this, i had to disconnect and reconnect the wires due to the way my gauge console is setup.

So after everything is buttoned up, i get nothing----no fan and the switch does not light up.

So, let's look at the diagram of the fuse panel:


This past whole year i was getting power to the switch from slot #1.   i took a test light and there was no power coming from #1 or #2, but there was power coming from #3, so that's what i'm using now and back to the original 2 prong switch because i need the fan more than i need the lighted switch because this is my daily driver.  The fan works fine now.

1) i'm thinking i "blew" something related to #1 and #2.  If so, what?   And how do i fix/reset this?

2) Do i now need a fuse going from the fuse box to the switch if i want to use the 3 prong lighted switch?  (My gut feeling is yes, but i'm not clear why?)   

3) What caused the problem?

[bd]

You don't need a redundant fuse to the toggle switch.  The HORN-DM fuse serves that purpose.  Check it.  You probably touched the wrong wire to ground, inadvertently.

[Rattler12]

 Per your second drawing.......why the ground to the terminal on the right side of the double switch ?   Power should go to the center terminal which powers each outer terminal depending on the switch position. With the switch in the left hand position you've got no current with that setup. I always thought power in power out on a switch to cut the power to the accessory.  I guess running power directly to the acc and then wiring the switch to interrupt the ground would work in a single throw switch but don't know why one would want it to work that way. I've always run power to the switch then the acc and grounded the acc,      who knows

[bd]

Rattler, the second drawing uses an "internally lighted" switch.  There are a few different configurations, but the most common style lighted switch requires a dedicated ground for the internal bulb.  The toggle switches power to two parallel circuits: one for the external load, the other for the internal light source.

[VileZambonie]

This must be quite annoying trying to remember to flip the switch. You can get an adjustable thermistor relay setup for less than $40 bucks. Wire it up on the ground side and be done with it.

[Rattler12]

I guess I don't understand what's trying to be accomplished here. If it is having a lighted indication of when the fan is operating to me it would be simpler to install a thermal switch into the intake manifold  which grounds the relay. When the water temp gets to 190 ( depending on the switch ) and it engages it grounds the circuit and activates the fan. Then run power from the fuse panel to a dash light and connect it's ground to the wire running to the thermal switch in the intake....no need for a toggle switch at all....?

[bd]

There's no question that a thermostatic control is optimum for operating an engine cooling fan.  Although a manual override is a nice "option," I would neither use it on my own vehicle nor recommend it to others as the primary control.  It's not only annoying, it's potentially destructive if you become too distracted to switch it on and off timely.  I use and recommend the Dakota Digital PAC-2750 and a dedicated sender, because of the integrated options and proven reliability.  I am very happy with it and that is not easy to accomplish.  The site store is a vendor for DD, but there are less expensive solutions.  As Vile stated, an adjustable thermistor relay is available for less than $40.  However, the OP didn't ask for viable options.  He asked why the posted circuit didn't work as he had expected.

[Stewart G Griffin]

You don't need a redundant fuse to the toggle switch.  The HORN-DM fuse serves that purpose.  Check it.  You probably touched the wrong wire to ground, inadvertently.

Yes, the horn fuse did blow.  It does seem likely that i touched a hot to ground as i had to unplug and replug the wires to get the switch into the gauge panel;  i had tested the switch outside the gauge panel at first.   i thought i had did this with the battery disconnected, but may not have.

Why would this cause the fuse to blow vs. just turning the switch on?   Because the switch provides some load while touching to ground made "infinite" load?

I guess I don't understand what's trying to be accomplished here. If it is having a lighted indication of when the fan is operating to me it would be simpler to install a thermal switch into the intake manifold  which grounds the relay. When the water temp gets to 190 ( depending on the switch ) and it engages it grounds the circuit and activates the fan. Then run power from the fuse panel to a dash light and connect it's ground to the wire running to the thermal switch in the intake....no need for a toggle switch at all....?

To explain why i wired it this way:
Yes, i agree that using a sensor and having the fan come on automatically is most likely the best way.  But at the time, i thought this would be the simplest way---for me.

i don't find it annoying and i've got the switch right next to the temp gauge, which i monitor while in traffic.  This past year the whole time i've only had to use the fan like 4-5 times.

[Stewart G Griffin]

You don't need a redundant fuse to the toggle switch.  The HORN-DM fuse serves that purpose.  Check it.  You probably touched the wrong wire to ground, inadvertently.

Yes, the horn fuse did blow.  It does seem likely that i touched a hot to ground as i had to unplug and replug the wires to get the switch into the gauge panel;  i had tested the switch outside the gauge panel at first.   i thought i had did this with the battery disconnected, but may not have.

Why would this cause the fuse to blow vs. just turning the switch on?   Because the switch provides some load while touching to ground made "infinite" load?

I guess I don't understand what's trying to be accomplished here. If it is having a lighted indication of when the fan is operating to me it would be simpler to install a thermal switch into the intake manifold  which grounds the relay. When the water temp gets to 190 ( depending on the switch ) and it engages it grounds the circuit and activates the fan. Then run power from the fuse panel to a dash light and connect it's ground to the wire running to the thermal switch in the intake....no need for a toggle switch at all....?

To explain why i wired it this way:
Yes, i agree that using a sensor and having the fan come on automatically is most likely the best way.  But at the time, i thought this would be the simplest way---for me.

i don't find it annoying and i've got the switch right next to the temp gauge, which i monitor while in traffic.  This past year the whole time i've only had to use the fan like 4-5 times.