heater grid relays

cumminspwr11

cumminspwr11

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May 18, 2010
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so something is wrong with my heater grid, i have it unhooked because if its hooked up its always on and never turns off, started when something fried my trucks computer and every electrical device inside, i put a new computer on and unhooked the relays, now its winter and my trucks IP is weak or going back because it doesnt start easy in the cold, no its not the injectors. if i plug it in at night it starts fine but i live in a apt. right now, im wondering if i can use a regular old napa relay (like the 7.3s do) to run my heater grid? that would help alot with my cold starts
 
Yes, if you don't want to run the factory set up. All you have to do is put a push button in the cab to the relays. Hold the button for 15-30 sec and fire it up. You will looses the cycling that the computer does to the relays when going down the road, but you should be fine. If you want to replace the factory relays you could do like I did :

here
 
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You said your IP is weak.. What happened to it?

Maybe your OFV is weak...?
 
toms73novass said:
Yes, if you don't want to run the factory set up. All you have to do is put a push button in the cab to the relays. Hold the button for 15-30 sec and fire it up. You will looses the cycling that the computer does to the relays when going down the road, but you should be fine. If you want to replace the factory relays you could do like I did :

here
Click to expand...

Do you NEED a relay or can you just run wires with a switch to turn it on/off? I haven't hooked my grids up in my fummins swap yet & was wondering...
 
TRUBBS said:
Do you NEED a relay or can you just run wires with a switch to turn it on/off? I haven't hooked my grids up in my fummins swap yet & was wondering...
Click to expand...

You would have to find a high amp switch that is a double pole - single throw or double throw. You would also have to run a bunch of high amp wire into the cab and back out. As you increase the distance of the wire you might have to increase the gage if it is over so many feet....

That is the reason that relays are used, keep distance down on high amp wire (more expensive and don't have to up wire gage for long run). Reduces the possibility of a fire from high amp draw short.

Personally I would still run a relay. But you could make a straight hook up work with the right components.
 
just run a relay they are not hard to do and they are easy to set up. Easier to find the parts needed and wont kill switchs.
 
relays are no problem for me and thats what i plan to do, just didnt not if there was something special with the factory ones because a smaller wire comes off the battery and a large gauge one goes form them to the grid, couldnt figure out if they were some short of coil or just a simple relay

as for the IP, when it gets cooler out my truck gets hard to start, i have check the injectors a few times and have even changed them and the problem is still the same, if i plug the block heater in it starts just fine and it starts fine all summer, the heater grid makes it a bit easier to get started, thanks for the help i will be finding a relay and get this wired up soon, i wish i had the money to get the pump rebuilt but i dont have that extra money right now
 
The smallest of fuel leaks will make your truck harder to start also, and more noticeable in cold weather
 
i starts up fine if its warm out or been plugged in and i have changed the rubber ones since this problem has been happening with no affect, i will be changing over to a electric fuel pump here pretty soon and re-plumbing all my fuel lines and adding a 2-mirco spin on filter so we will see how it goes and if it helps out at all
 
I've read in several places that the grid heater controller for the early 89-93 dodges had a stand alone controller.

Can anyone confirm that. Avoid the whole push button grid heater thing? I'm sick of the damn buttons.
 
You can also diagnose the current relays by popping off the signal wires and seeing if your grounds are switching on and off or not, if they are working correctly then you can wire in some jeep starter relays for around 12$ a piece and they will work like factory, but cheaper and more durable.
 
so one of the two smaller wires that go to the factory relays is a ground wire? can some clearify how the stock ones are wired on a 95? i just picked up a jeep relay, still need to get another one or can i use one relay for both wires? autozone only had one available right now, i would like to wire up the new relays to work off the stock ignition switch
 
If I remember correctly the solenoid needs to be isolated, I mounted the jeep relays on top of my plastic fuse box cover

I believe the relays are wired separately because not both are always used

Also the jeep relays I used had three terminals, but only two were used for the switch.
 
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If your going to try and set it up like the factory wiring, yes the relays HAVE to be isolated.

The relays trigger coil sees a constant +12v with the key on, and the PCM switches the ground side of the trigger coil off and on to activate the relay.

If the relay is replaced with a non-isolated unit, the relay will activate as soon as you turn the key on because it is already grounded!

If you are going to run your own complete setup, you can run a non-isolated relay (keep in mind each GH element draws ~90amps, so size it accordingly) and just use a push button switch on the dash to sent a +12v trigger signal to the relay.
 
your going to need big relays, these things suck up a ton of power, iirc factory is 2 relays working as a 1 I was told they pull over 100 amps i don't know if its true but it seems right
 
Each grid is ~90amps, each factory relay is rated at 100amp. they operate independently depending on conditions (the PCM may fire only one or both grids pre or post heat)
 
Heres a cool little chart of how the cummins GH controller operates. The dodge PCM is programmed similarly.

gridheater.jpg
 
Great information ykdave, I had been interested in the specifics for some time
 
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