OK heres whats been plaguing me for about a year now....Its getting cold again and need to go easier on the truck. I have power down to my grid heater relays, but when I turn the keyswitch on, the relay clicks on and I lose all power to my relays, it even shows no power to the relay wire terminal where it mounts to the battery terminal bolt. I just replaced the relay and same thing. Any thoughts?

 

Here is another question. Does it matter which side I have the small wires on the relay installed, I have an orange/black wire and a black wire to the front relay and a yellow/black wire and a black wire to the rear relay. This truck is a 2000, if it does matter, which goes where?

 

according to my manual, it's right .......

 

I'm no expert, but I did just do a little trouble shooting with my 98.5 truck and the intake air heaters. Here's some of the stuff I learned that may help. I've done a search for some of the threads where I found information, but can't seem to find them now...

First check the codes. Is the check engine light on? If not then there are no codes. If so, is your truck new enough to get codes by cycling the ignition key (without starting) 3 times? I think that the codes will dispaly in the odo if you do that. Knowing what codes you have would be the first step in troubleshooting.

Without a wiring diagram, I wouldn't know how the switch wires would connect, but you can get a test light or Ohmmeter and use that to find out. Don't forget to wait unitl it's cold to try it though... Also, is it cold enough to get your grid heaters to turn on? I think it's 66 degrees or colder. The day that I was working on mine, it was too warm and I had to wait for a cold morning to find out whether I had actually fixed the problem.

Other sensors play a roll in when the heaters turn on. I think it's the air intake temperature sensor and the battery temperature sensor. I don't know where either of those are, but I imagine that a bad sensor could fool the computer into thinking that it doesn't need to warm the heaters.

From your description, I would imagine it's one of a couple of things. Again, I'm no expert... The switch wires are connected wrong. The wires themselves have been severed. The computer isn't receiving the correct signals from a sensor. Something in the mechanism to actually energize the switch wires is broken.

To test if the relays are working correctly, here's what I would do: Get some test leads with alligator clips on the end. Remove the switch wires from the wiring harness and connect one of the switch terminals on the relay to the positive terminal on your battery. The using another test lead, ground the other switch terminal on the relay to the negative terminal on your battery. Be very careful not to touch the grounded lead to the top of the relays. You should hear a "click" and if you measure voltage across corresponding grid heater connection on the intake manifold, you'll get about 12v. Then do the other one. If the relays check out, well then you know they're not the problem.

Hope this helps.

 

If you are getting no power at the battery terminal you need to look very hard at your cable connections at that point. If there is ANY corrosion in the area, clean it up. If I understand you correctly, everything is fine till it gets cold enough to need the intake heaters. Then, when you turn on the key to start it, the relay(s) click, but the power goes away from the supply side of the relays. If that is the case, the problem pretty much has to be between the relays and the battery. On my '99, that's about 18 inches of 6 gauge wire.

 

The solenoids are not polarity sensitive.

 

Well, I don't know what I did but it works now!!! With a better tester I wasn't losing power at the battery terminal like I thought. I took out the iat and cleaned it and checked it with an ohm tester, I guess it works, if it acts up again I'll change it. The only other thing I did is unplug the pcm wire harness and attempt to check wires there, put it together and presto. I think it helped having a better wire tester, it wasn't reading correct last night. Thanks to each of you for your help, i appreciate it. Now I'll hope it works in the morn.