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Switched Grid Heater

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I finally figured out how to get the grids on a switch. By utilizing the positive wires that energize the grid heater relays, you are able to take control of when the relays energize. To do this, all you need to do is put a switch somewhere between those wires so that you are able to close or open the connection and therefore keep the relay from energizing. The two wires you will need are the orange and black one, and the yellow and black one. The other 2 wires are green and are the ground. You can switch either one, the ground or the positives. I chose the positives because I only used one switch. Having 4 batteries, I do not see the need to only be using one grid, so I connected both positives together so that when just one energizes, it still energizes the other so both grids always turn on. This has a drastic effect on how long the grids stay on during the on/off cycle after the truck starts, they only stay on for half as long since they have twice the heat output. For all normal purposes however, I would use two switches OR you can connect the grounds together (which connect together upstream somewhere anyways) and use just one switch that way, and the grids will stay seperate (they will each turn on individually instead of the way I have it set up). I am not sure if 1998+ trucks will throw a code, there are many codes listed but I can exactly find one that will trip for this very isntance, someone with 1998+ will have to see. Trucks 1997 and below will not throw any codes.Here you can see the voltage drop a lot since it uses both grids every time.

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It's not that hard to do. Just glance down and see it lol. I have more trouble seeing around that huge pillar so I had no desire to put gauges on it to make it even worse. After a while you get to the point of knowing exactly where the gauge is at and when you need to be letting off without ever having to look at the gauges.

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A 3rd gen! Can't help you at all there though :lol: Worst comes to worst you could put in another relay on the leads going to the grids, but it would have to be pretty beefy and the whole speil would end up costing a shiny new shield faced penny.

--- Update to the previous post...

I have never seen such a crappy writeup (first post on this thread). I just got to thinking and if I had tied the grounds together and switched them instead, the grids would still work individually with the switch on since it's the positive that does the energizing. Might have to redo it on my truck. Man I feel like an idiot! I will get it right one of these days. :mad:

I do have a question for you 2nd gen 24V guys who can clear codes easily lol, does it throw a code if you take only the positive (orange or yellow) wire off one of the grid relays? Does it throw a code if you take only the negative (green) wire off one of them? I'm trying to understand how it even knows to throw a code.

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A 3rd gen! Can't help you at all there though :lol: Worst comes to worst you could put in another relay on the leads going to the grids, but it would have to be pretty beefy and the whole speil would end up costing a shiny new shield faced penny.

--- Update to the previous post...

I have never seen such a crappy writeup (first post on this thread). I just got to thinking and if I had tied the grounds together and switched them instead, the grids would still work individually with the switch on since it's the positive that does the energizing. Might have to redo it on my truck. Man I feel like an idiot! I will get it right one of these days. :mad:

I do have a question for you 2nd gen 24V guys who can clear codes easily lol, does it throw a code if you take only the positive (orange or yellow) wire off one of the grid relays? Does it throw a code if you take only the negative (green) wire off one of them? I'm trying to understand how it even knows to throw a code.

Yes... P0380 or P0382... It can detect a open circuit...

P0380 Intake Air Heater Relay #1 Control Circuit Problem detected in #1 air heater solenoid/relay circuit (not heater element)

P0382 Intake Air Heater Relay #2 Control Circuit Problem detected in #2 air heater solenoid/relay circuit (not heater element)

That why I disconnect the positive lead going to the grid heater supply...

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to do this correctly without issues, you would need to use another relay on the hot wire to the heater, or insert a switch on the small wire to the relay itself and break a small current rather than a large current.ancient revivals

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to do this correctly without issues, you would need to use another relay on the hot wire to the heater, or insert a switch on the small wire to the relay itself and break a small current rather than a large current. ancient revivals

All I did was put a switch on the small wire, wired it into the cab to my switch then back to the grid relays. I remember having issues between whether to use the green wires or not (back in 2010 when I was still learning), but looking at the schematic, the green wires are always connected and it is the hot ones that are switched. Meaning you would use the green ones to switch the entire system on and off. Or you could do the hot ones individually to control both grid heaters since the system may or may not use both during different times. I used the green wires and it worked perfect, killed the whole system at the flip of a switch.

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Ok cool. I am going to get a hold of an amp clamp this weekend maybe and see what they are drawing. It might just be how cold it is out that is the problem. After I run the grids twice there is not enough juice to crank the truck over. 2 brand new 900 CCA batteries and a new alternator a couple weeks ago. Either the grids are drawing to much or I have a serious power draw while the truck is off, or its just to cold.

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Do you have the truck plugged in?

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With brand new batferies you should be able to cycle the heaters many times and still be able tovstart your truck. I have junk batteries and i can cycle twice and still start. Take both positive cables off the batteries. Hook a test light between the positive clamp and positive post on one of the batteries. If you have a major draw the light will be bright. If you dont it will just barely light up. Pull the iod fuse and if you still have a light on then start pulling fuses until the light dims or goes out. Anytime you open a door or use anything that uses power the light will brighten.

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Your truck shout start right up without cycling the grids when it is plugged in all night. Mine doesn't even hardly run the grids at all no matter what the temp is. Are you sure your heater is functioning? I had mine plugged in for three days and even the upper radiator hose had heat in it.

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I am pretty sure the heater is working but I'll check tomorrow after it has sat all night. But even if it wasn't working I should be able to cycle the grids more than twice before running the batteries dead I would think.

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Ok. I have a test light in between the cable and battery. I made sure there isn't anything plugged in to the cig lighter/power port and all doors are closed. The test light seems to be pulsing steadily. It's a pretty bright pulse but I have no idea what would cause that. It's about twice as fast as a turn signal pulse. I'm going to start pulling fuses until it stops.

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Ok. Without anything plugged in in the cab there is only .008 amps being drawn through the IOD fuse. I plugged my stuff back in (i.e. cell charger, radar detector, etc) and it came up to about .15 amps being drawn from the batteries. Not enough to bring them down over night I wouldnt think.

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