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  • Switched Grid Heaters

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    Switched Grid Heaters

    For those wanting a switched grid heater, here is how to do it on a 12V from 1989 on up to 1997. The 1998+ trucks throw a code (P0380 and P0382) so for those with that system, you will have to just disconnect the leads that go to the grid heater itself. When winter comes, just reconnect them.

    The reason for doing something like this is because the truck will run the grid cycle if you run into the store or something and this is not necessary and is a load on the batteries and alternator, so why have it when it’s not needed during these scenarios.

    The controversy begins when you use it as a selector switch as to if you want to use the grids at all at a said temperature. The truck will start fine down to 32F and below that it will still start fine but is much happier with the grids. The problem is, this is very hard on the engine when it has to start with nothing but the heat of combustion. The temperature at which this degradation occurs is unknown but it’s a safe bet to say that 50F and below should be using the grid heater. The grids will still cycle up to 60F, but I think that last 10F is a buffer zone that is up to you.

    Why use the grid heaters at all?

    If you choose to remove the grid heaters or disable them, there are a few consequences of that action. All I will tell you is that starting it cold with no grid heater will make it hate the cold. My truck started up with no smoke, on the first crank, with no grid heater at 0F when I first bought it, this was even at 250k miles. The next year, it was starting the same, but I HAD to use the grid heaters. Don’t push your luck with them, use them every chance you get.

    What about my batteries?

    Driving short distances in the winter is the worst thing ever. Your grid heaters are going full blast on the morning start and your battery is getting killed. It will last a little while, maybe a week doing these cold short driving stunts. After a week, you really need to drive it for a long distance or charge the batteries using a battery charger or even exchange them with another vehicle that drives long distances.

    Hooking up the switch

    On the driver’s side fender well, there are the 2 grid heater relays. They control the 2 grid heaters individually. The positive wires (orange and yellow) are controlled by the ECM and are what turns the grid heaters on and off. There are 2 other wires that are green (one on each relay). Those are the wires you want to tie together and put a switch in between the ground source and the relays, thereby making the relays have no ground when the switch is off and having ground when it is on. This way, the grids will work exactly the same as stock when the switch is on. It is also easier as you only need to run one wire from the 2 relay grounds, to the switch in the cab, and then any good ground inside the cab.


    In this video, you can see the grid heaters being switched on and off, the ECM continues to cycle, it doesn’t know that they really aren’t cycling. This allows you to turn the switch off and if you turn it back on and the ECM is still signaling the relays, they will work when you turn the switch back on without anything knowing the difference. The clicking is the switch being turned on and off, you can see the voltage drop when the grid is on.

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