dual electric fans ii

three tabs on switch, call them ignition, relay 1 and relay 2, ...AC connects to relay 1 and relay 2 through the diodes.

Right, banded ends to R1 #86  and R2 #86, 1 each to outer tabs on switch, 12v to center tab.  That should be how I have it on the diagram...?

Basically, I wire each as if they are on own switch and merely add 3 diodes to do the rest? 

#1 diode jump between outer tabs on switch

#2-3 diodes to R1 #86 and R2 #86, connect and run to AC positive......

Not nearly as complicated as I thought, thx.

My Super Custom Signature....

correct, you're welcome.

If you use ground switching, no didoes are needed. Just parallel all the grounded sensors and switches that you want to turn a particular relay on.

Im sorry, I dont understandMy Super Custom Signature....

When you have multiple inputs using +12V, you need isolation diodes. If the inputs are GND, you don't. EG - instead of having sensors & switches supplying +12V via diodes so that a relay or load will be on with any or all, if they instead supplied GND to a "hot" relay or load (ie, the other end is to +12V), you just join them together (eg, to relay #85). However, if you need to isolate one grounded signal from another, you'd still need diodes. But that isn't required if the sensors or switches ONLY control the relay or load.

Grounds from switch to relay 85, 86 to ignition, job done.

I appreciate the help guys, but honestly I'm more confused. I'm more of a visual learner, would it be possible for you to modify the diagram I posted?My Super Custom Signature....

Still has AC system, which has positive control. Just as easy to go positive, plus wants isolation of aux fan. Would need DPDT switch plus additional relay to invert AC control output.

Then stick to the +12V switched system as is. It was merely a consideration. I have occasionally used GND switching with the occasional polarity converter for the odd input - eg, AC sensor if it can't be connected to GND or of it controls another circuit that likewise cannot be converted (often they switch relays). GND switching often overcomes the need for diodes, and fuses for switches. And it's great when switching circuits with different voltages or from different +ve supplies - eg, from different fuses.