The defroster in my 2005 tb is not working. I have checked the voltage at the leads and I am getting different readings that range from 14 volts to 3 volts. I have checked the boot where the wires come through the lift gate, but cant get the boot off completely in order to see if there is any thing wrong. what is causing the variation?
rear defroster not working
- Thread starter bob
- Start date
There are possibly problems in the wiring getting TO the grid (both the hot side and ground) and you could have open wires. Check this: Frost Fighter Defroster Troubleshooting and Repair Resource
I too have this issue. Started at the end of last winter, so early this year I think.
I check the grid and all seemed fine. Also a 2005 TB.
I check the grid and all seemed fine. Also a 2005 TB.
How did you check it? Was there power and ground at the tabs when you turned it on?misterhyde said:
sorry, I meant visually I check it. I guess I should throw the voltmeter up to it and check continuity.
Visual checks are low down the list of things I trust. I constantly wish my retinas would distinguish voltage when I look at wires. 
Check continuity with the power off, then check for +12 and ground with the power on. If you have any dead lines in the grid, get a pin to use for one voltmeter lead, and check the voltage gradient across the dead line and it should lead you right to the gap, which can be fixed with conductive epoxy paste.
Check continuity with the power off, then check for +12 and ground with the power on. If you have any dead lines in the grid, get a pin to use for one voltmeter lead, and check the voltage gradient across the dead line and it should lead you right to the gap, which can be fixed with conductive epoxy paste.
I've got the same problem with mine. Only when I look at my back window to where the little tabs are located the one on the driver side of the window is not even close to being located in the correct place. its mounted on the window just not in the correct spot. I'm assuming this is my problem but I will find out tomorrow. I did the visual inspection for broken parts today because my voltmeter is at work.
the roadie said:Visual checks are low down the list of things I trust. I constantly wish my retinas would distinguish voltage when I look at wires.
Check continuity with the power off, then check for +12 and ground with the power on. If you have any dead lines in the grid, get a pin to use for one voltmeter lead, and check the voltage gradient across the dead line and it should lead you right to the gap, which can be fixed with conductive epoxy paste.
So I took the voltmeter too it as I was out doing some other things to the truck.
7.4v from the tabs. I then checked continuity, 1st with audible and it buzzed. Then put it on 200 and got 1.## (can't remember). Not sure it it gets multiplied by 100? Either way, I think my grid is good. Pretty sure someone said its supposed to be 12v?
Anyway, my neighbor thinks that the switch in the console is bad. He says sometimes they wear out or get grimy.
Sparky
Member
- Dec 4, 2011
- 12,927
The switch in the dash is just a button. It triggers a relay. If the light turns on in the dash, the button is fine.
7V sounds wrong. You either have bad contacts on the relay, a bad ground side, or faulty wiring. What I would do first is turn it on, then test the voltage hot side to a different ground and see if you have 12V that way (Well, 13-14 volts actually if the engine is running). This would isolate whether you have a problem on the ground side or the power feed side of things.
7V sounds wrong. You either have bad contacts on the relay, a bad ground side, or faulty wiring. What I would do first is turn it on, then test the voltage hot side to a different ground and see if you have 12V that way (Well, 13-14 volts actually if the engine is running). This would isolate whether you have a problem on the ground side or the power feed side of things.
Sparky said:
k, makes sense. Any idea on what I could use as a ground back there? body of truck?
I am wondering if I did the Big3+1 upgrade around the same time. I have good contacts at the battery and the body point next to battery. I just check and ground those to good metal. Now, I have been having other electrical issues, and am starting to think it might be from the big 3. I left the positive cable from the alternator to battery, but added a thick multi-strand cable to the same points. I also added a ground to the front bracket bolt, as you can see in the pic I took of my efan.
I thought maybe it had to do with the efan setup? dimming the lights when it comes on, but I am also getting a weird flutter of the dome lights (all of them) all of the time they are turned on.
Any unpainted part of the body, or a screw or bolt head. Or scratch through the paint in an unseen area. Lots of folks (not you) assume that black wire grounds are always trustworthy, and especially in the case of the liftgate, they are not.misterhyde said:
Think of the power wire as a conductor that has to deliver 12V with low lossage to the load. A partial break in the wire adds resistance, and resistance steals power. Instead of delivering let's say 10 Amps (120 Watts) to the load, a high resistance in the path might steal half of that power, so only 60 Watts, or 6V, gets delivered to the load. Since current in a series circuit can't disappear (a fundamental rule of electricity), what happens is that voltage is used up in the wiring and connections instead of being fully delivered to the load.
But ground wires can be thought of the same way. A ground wire is a conductor that is supposed to deliver ZERO volts to the load. A place where the current can drain out and get to the frame or body of the truck, and then flow freely back to the ground side of the battery or alternator.
A bad ground wire will not be sitting at zero volts, when compared to a known good ground like a frame screw head.
That's why it's most useful for troubleshooting to make two measurements with your meter to the defogger grid terminals. One from a known good ground to the 12V side, and another one from a known good ground to the "ground" side of the grid. Then you know if your high resistance problem is on the current delivery path or the current drain-off path. Thinking about electrical current as water flow, and voltage as pressure, and switches/relays as valves, and wires as hoses, is the way I usually discuss it with folks new to the concepts.
bore_pig
Member
- Nov 25, 2011
- 113
Well stated Roadie.
A good place to look for a bad connection is at the connections to the grid. The last rear defrost I had to fix had a poor connection on the ground side. The guy said "I have 12v to ground on both sides, can't see why it isn't working". Earned myself a quick case of cold ones that day.
A good place to look for a bad connection is at the connections to the grid. The last rear defrost I had to fix had a poor connection on the ground side. The guy said "I have 12v to ground on both sides, can't see why it isn't working". Earned myself a quick case of cold ones that day.
WarGawd
Member
- Sep 2, 2012
- 468
Discovered I also have rear defrost problems - without checking anything yet it seems like power and ground to the tabs must be ok, since the grid line immediately above and below the tabs are the only two that work. Just makes it difficult to picture in advance what's wrong with all the others. I'll take a DMM to it tomorrow and see what's up.
WarGawd
Member
- Sep 2, 2012
- 468
Meter wasn't really needed - I could see the gaps where the conductive material was missing, as if it had simply peeled away from an adhesive backing. The residue of that backing was all the was left in those areas. I tried the Permatex paint on grid repair - despite following the directions it just lifted back off when I removed the stencil/masking. If I decide to try this again, I will remove the stencil before the material has any chance to cure and see if that gives a better result.
Any opinions on whether I should also scrape off the residual adhesive before applying the paint? Seems to me if it's still stuck to the glass, then the paint will adhere to it better than to the glass directly (as long as it's clean & grease free etc). But maybe I'm wrong...any thoughts or experience with this?
Any opinions on whether I should also scrape off the residual adhesive before applying the paint? Seems to me if it's still stuck to the glass, then the paint will adhere to it better than to the glass directly (as long as it's clean & grease free etc). But maybe I'm wrong...any thoughts or experience with this?
My 06 TB has this prob too...anyone got any pics of their tabs on the glass...I have power to every line but it must be weak,because it will not melt snow or even frost.
Okay, resurrection time 
a few weeks ago found that one of the tabs had a crack where it bent over to accept the connector. So ended up pulling it off the window, soldering the crack, and gluing it back on with the defrost tab glue from Carquest ($11!!!!)
Put it back on and still no thawing. Got our first snow yesterday here in central MI (frozen rain first) and really missed the rear window defroster this morning.
So, I go to the manual and look to find the Rear defroster fuse & relay. Much to my dismay, there is none labelled. WTH?
How do I find it, or is there one?
How do I fix a bad ground to the system? Is there a single grounding location for the defroster?
TIA
a few weeks ago found that one of the tabs had a crack where it bent over to accept the connector. So ended up pulling it off the window, soldering the crack, and gluing it back on with the defrost tab glue from Carquest ($11!!!!)
Put it back on and still no thawing. Got our first snow yesterday here in central MI (frozen rain first) and really missed the rear window defroster this morning.
So, I go to the manual and look to find the Rear defroster fuse & relay. Much to my dismay, there is none labelled. WTH?
How do I find it, or is there one?
How do I fix a bad ground to the system? Is there a single grounding location for the defroster?
TIA
It's uselessly labeled LGM2, rear fuse #3, 30A. The relay is built into the LGM, not the fuse block. Grounded by G401, a ring lug on the driver's side of the liftgate opening. Problem could be the fuse, the power wire getting to the LGM by way of the hinge area rubber boot, or the ground wire also going through the boot to the body. Or the LGM. Or (for future researchers) if other functions in the LGM are dead like wiper or remote entry, then suspect the data comm wire going through the hinge area.
FIXED (I Assume)
Well, I was able to dive into the hatch area again this weekend (60 deg. F mid-november sucks for MI Gun hunters like me)
I kept remember members saying they found frayed wires in the area around the hatch hinges. So after checking fuses and wires and not seeing a problem, I saw there was one more area I did not look yet.
The Bottom portion of the boot.
View attachment 31357
Well, I was able to dive into the hatch area again this weekend (60 deg. F mid-november sucks for MI Gun hunters like me)
I kept remember members saying they found frayed wires in the area around the hatch hinges. So after checking fuses and wires and not seeing a problem, I saw there was one more area I did not look yet.
The Bottom portion of the boot.
View attachment 31357
