Hello. I don't know squat about electronics. However, maybe someone here can help. I replaced my engine driven fan on my 2007 with a set of electrics fans that are wired through a 30 amp fuse for each of the two fans. However, the fans are messing up my water/meth injection controller. The water/meth controller pumps a mix of water/meth into my intake manifold based on turbo boost. When my electric fan kicks in, the controller’s reading for boost and the temperature of the exhaust on its LED display go to zero. The display still works/lights up etc, and displays text, but just reads zero for boost and exhaust gas temperature (EGT). I have a mechanical turbo boost pressure gauge and a mechanical temperature gauge for the exhaust also. These, being mechanical, keep working fine. If the truck is making 10 lbs of boost then the cooling fans kick in for the radiator, the boost and EGTs drops to zero. When the fan stops, the boost and EGT readings return from zero to whatever they should be (10 psi/800 degrees). The boost is picked up via a plastic tube and routed to the water/meth controller which is digital in nature. The electric fans are controlled by a pulse width modulator to allow for a variable speed setup. The fan controller is mounted to the radiator’s metal cross member. I have two batteries in my truck. To further isolate the water/meth controller from interference, I completely removed the +/- of one battery and ran both the ground and positive wire from the water/meth controller and its injection pump to the isolated battery for power and ground. Nothing in the water/meth controller or pump setup touches the truck or the truck chassis and it still stops working when the fan turns on. For more trouble shooting, I have trapped 4 psi of air in the controller tube for trouble shooting purposes. So, the gauge always reads 4 psi weather the truck is running or not so I don’t have to actually drive to make turbo boost. However, the instant I connect the fan and the fan turns on, the boost and EGT readings go to zero. Unplug the fan or turn them off, the boost and EGT readings comes back. I'm guessing is the problem is RF noise. How do I stop this? I don't know anything about capacitors. However, back in my youth, the electric motors in my radio controlled cars ran capacitors on the motors to keep from interfering with the radios. Please don't use technical stuff like thin film or what ever, which means nothing to me. What I'm looking for is:
Hey, put a 100 whatever capacitor between the + and - of the motor and see if that helps. The fans are both wired to a 30 amp fuse, so I guess the capacitor needs to be 12 v and handle up to 30 amps? Just a guess. Thanks to anyone who can help.
Also, tonight I made a very strange discovery. The fan is multi speed. When the fan is on low, the controller functions as stated above, messes up the water/meth controller. HOWEVER, when the fan switches to medium speed, the boost starts working again. Here is the funny part……….
When the fan switches from low to medium, the MECHANICAL boost gauge (not the one built into the water/meth controller, goes up by up to SIX psi instantly. The turbo has veins that move to change boost and are controlled by the truck’s computer. I can hear the turbo spool and my butt can definitely feel a slight pick up in acceleration. So, at cruising speed of about 65mph and the turbo making about 5 psi boost on the mechanical gauge and the fan is on low, the water/meth controller is not working... then the fan kicks to medium, and the controller starts working, and the mechanical boost gauge raises to 11 psi. This is a real gain in boost from the feel and from hearing the turbo. Its not extra horse power from the water/meth since it is not injecting AND the pump is disconnected anyway for trouble shooting. When the fan drops to low, the water/meth controller stops reading, and instantly the boost on the mechanical gauge drops back to 5 or so. What do you all think? Some thing isn’t right here. How can the fan cause the boost to change unless it’s also messing with the truck computer and not just the water/meth controller? The fans have their own temperature sender unit in the upper radiator hose and don’t interface with the factory computer in any way.
I cannot return either unit since they were installed.

Picture of the controller and installation location?

Sure give a day.

Try wiring the fans direct, both + and - direct to battery + and -, forcing them to high speed. If this keeps every thing in check, you might have to wire the fans to just come on high speed when needed and totally off in-between times. PWM's are notorious for trash emi.

I'm not very familiar with your equipment, so I cant comment on the oddities of the operation, but one standard procedure for reducing/eliminating Radio Frequency Interference (RFI) is to install .01 mfd disc ceramic capacitors as close as possible to the source of the RFI. The idea being to bypass the RFI harmlessly to ground rather than allow it to radiate. The capacitors are available at radio shack or any TV repair shop and are pretty cheap. Dont worry about the voltage rating - they will all easily handle 12 VDC. They dont conduct any DC current so it doesnt matter how many amps the fans or whatever will use. The capacitors are installed with one lead connected to the suspected RFI source (+ wire from the PWM, for example) and the other lead connected to ground. Usually its kind of an educated guess where the source of RFI is and you may have to try several different spots or install several capacitors. One trick that sometimes works, but I dont know if it would work in an engine compartment is to tune a small portable AM radio to a blank space on the dial. You may be able to hear the hum or RFI hash. Move the radio around until the noise is the loudest and that will be pretty close to the source of the RFI.

I'm done, giving up. Sendiing all the parts, inc snow controller, to SPAL to trouble shooting. THanks all.

Are you grounding all the equipment to a common ground? With PWM especially, any 'ground loop' noise will interfere with the controllers ability to change the on time of the power switching.

All were grounded to the exact same point, then varrious other points, still the same.