Replaced batteries last month and a few days ago my voltage started dropping and the check gauges light come on. Voltage dropped to 0. I rechecked the batt cables and it worked good for a few days. Yesterday the voltage dropped again. Turn the key off and wait a few minutes, restart and gauge started working. Worked fine today, so I started checking other stuff and I noticed that my intake base on top of the grid heaters was burnt looking and the heater housing is burnt looking along with the plastic insulator on one of the heater wires is melted.
What controls the heaters after it warms up? It looks like they are staying on and is that causing my voltage drop?
Any help appreciated.

 

I believe the intake air temperature sensor (IAT) dictates when the grid heaters come on and go off. I would check it, and the relay.

 

If they are staying on at road speed, the heater relays are probably sticking. When the speed reaches something like 25 mph, the heaters stop working regardless of temperature.

 

Are the grid heater relays a dealer part or can you buy after market. I think atleast one relay is probably stuck causing the heater to stay on. Will Probably replace both relays.

 

Mine started sticking and would completely drain the batteries. Upon close inspection I found that the case on one of the solenoids was cracked allowing water/dirt to get in. If one of the solenoid sticks the grid heaters will stay on with the ignition key out!!

I tried finding OEM parts to no avail, had to settle for original parts. They take came as a 1 piece assembly , about 10 minutes to change.

 

The grids are controlled by the ECM, which senses IAT (intake air temp) and ECT (engine coolant temp). It uses primarily those two to determine if activating the grids is necessary.

Typical parameters for grid heater activation (10 seconds)

ECT - under 140ºF
IAT - under 59ºF

Typical for grid heater activation (30 seconds)

ECT - under 140ºF
IAT - under 30ºF

The grids are not activated above 60ºF IAT, even though the wait to start light stays lit for 2 seconds.

The ECM will cycle the grids to aid in engine warm-up after the engine is started. They will cycle until one of the following conditions are met:

ECT reaches 140ºF
Truck speed reaches or exceeds 23 MPH (this varies between trucks).


In the event of relay failure, I know that you can swap in a Ford starter solenoid (very common item in parts stores). This option requires some modification to use, but if you are decent with wiring, it should be fairly straightforward.

 

What caused my heaters to stay on long enough and get hot enough to burn the outside of the heater housing and the lower part of the intake tube? And hot enough to melt my turbo boost line.

 

Try wiring a temp light to the grids so that when the grids are on the light lights up in the cab, this way when driving down the road you will know that they are on. the melted connections could have been caused by loose connections, but if its killing your batterys, you need to figure out if the ECM is turning them on or that the relay is at fault and its working independant of the ECM. I do know that just about any type of hi-amp relay can and will "stick on".
try running an in cab test light to the small signal wire on the relay as well as a test light to the grid, go for a drive and see which lights come on

 

Man im having the exact opposite problem...my grid heater will not turn on

 

my relay stuck winter before last.same as you describe.replaced solenoid under drivers side battery.

 

I have read somewhere you can use ford starter relays.

 

You can, if you are decent at working with wires that is. The grid heater relay (as nickg indicated) is nothing more that a high current relay. This is because the grids draw about 190 amps of 12V power .

The starter solenoids are designed to handle a lot more current (amps) that the grid heater relay, because they are designed to control a starter motor.

Re-fitting a Ford starter solenoid is a popular option, because the Ford solenoid was used in a wide range of Ford vehicles, for many years. They are easy to find at any auto parts store, and are relatively cheap (about 10-20 bucks).

 

http://search.cartserver.com/search/...=GO!&bool=AND1

Don't know about 24 valve, but the old first gen relays, appear to be the same as the western plow ones, which can be had for reasonable.

 

Ok, it's been over a week now and since I disconnected the grid heaters I've not had any more trouble with the batt gauge. Now this is werid, about 2 weeks ago I posted a question about injectors and the problem I was having about not running right and acting like the engine was not getting the fuel it needed. Well i've not had that trouble any more either. Could the grid heaters being on all the time and the hot intake air cause that. A buddy of mine is checking on new heater relays for me. I will get back after I replace them to see if everything goes back to normal.

 

Anyone who is interested, I found a website where you can buy the grid heater relays that are the same as the stock one's at a resonable price.
http://www.rockauto.com