FJ62 rear defrost voltage (1 Viewer)

[Spook50]

Messing around with the rear defroster on my 62, and I have a few ideas to try in order to see if I can improve its function. Most lines on the grid are (surprisingly) still good. Just a couple that are shot. Last night I checked voltage on the leads connected to the grid, and showed only 10.1 VDC . I'm curious if this is on par with what others are getting on their defrosters.

My intention is to start with a larger ground lead, and then add an actual ground wire from the lift gate to the body itself so that it doesn't ground through the hinges like seems to be the case. After that I'll use a larger power lead from the relay, into the lift gate and to the grid. I have yet to see exactly what voltage I'm getting from the high current lead on the relay though, so if that is also only 10.1V I won't bother. But if it's considerably higher I'll go ahead.

Eventually I'll adhere I whole new defrost grid to the glass when I pull the lift gate off for repair and repaint.

If anyone can check the vintage at the tabs for their rear defrost, I'm curious to compare.

 

[86aggie]

The repair manual has a page for troubleshooting/repairing the grid, with expected voltages at various points.

 

[CruiserTrash]

Messing around with the rear defroster on my 62, and I have a few ideas to try in order to see if I can improve its function. Most lines on the grid are (surprisingly) still good. Just a couple that are shot. Last night I checked voltage on the leads connected to the grid, and showed only 10.1 VDC . I'm curious if this is on par with what others are getting on their defrosters.

My intention is to start with a larger ground lead, and then add an actual ground wire from the lift gate to the body itself so that it doesn't ground through the hinges like seems to be the case. After that I'll use a larger power lead from the relay, into the lift gate and to the grid. I have yet to see exactly what voltage I'm getting from the high current lead on the relay though, so if that is also only 10.1V I won't bother. But if it's considerably higher I'll go ahead.

Eventually I'll adhere I whole new defrost grid to the glass when I pull the lift gate off for repair and repaint.

If anyone can check the vintage at the tabs for their rear defrost, I'm curious to compare.

When I was repairing the rear defrost on my previous 60 I was getting 12+V at the hot lead. As @86aggie said, the Body & Chassis FSM gives voltages at points along the grid lines - I think 5.5V was the expected voltage in the middle, for example.

I was getting no power to the grid at first, and found the wire halfway cut inside the rubber tube that goes from the headliner area into the upper hatch. I repaired that and was getting something like 9-10V. Behind the driver side cargo panel were a bunch of harness connectors that were extremely corroded. Check those - you could be seeing a voltage drop there (or anywhere along the path). I had larger corrosion issues (inside the wiring itself!) so I rebuilt the entire harness from the rear door back - I gutted and hardwired everything, no connectors. I left the taillight pigtails, but really everything else was replaced. Voltage at the positive defrost tab (driver side) was very healthy after that.

But the defrost still didn't work super well. In my new 60 I get healthy voltage to the defrost and it works only marginally better. I think the rear defrost on 60s might not be the best design.

FYI if you have grid lines that are broken, you can use a conductive paint pen to bridge the gaps. Tape it off with blue tape a little fatter than the actual grid line and apply 2-3 thick layers. PO of my red 60 put stickers on the inside of the window, and removing them lifted a bunch of the grids. The conductive pen got them all working again.

 

[Spook50]

The repair manual has a page for troubleshooting/repairing the grid, with expected voltages at various points.

It does. But like @CruiserTrash said, the design overall is marginal at best even with everything working well. My curiosity was what others are seeing at their grid tabs so I could have an idea of an "average" among trucks as old as ours. I think the best solution will be repairing anything that could be preventing full power (voltage AND current) from reaching the tabs and then pulling the glass to apply an entire new, modern grid. Also pondering if applying ceramic tint (I would opt for clear) might help protect the grid itself for longer term functionally.

@CruiserTrash I've done the conductive paint repair before, though in my experience it's never worked well beyond one season. What I used was the Permatex parts store stuff. I'm curious though if there are better products available now since it's been over ten years since I last did it.

 

[OSS]

My suggestion:

Run a big fat gauge test wire pair directly from the battery- or better yet, place a charged battery on the tailgate,and wire it directly to the leads of the defrost net and see how it performs.
That test hookup will show you if wiring bigger gauge wire eventually through the body will be worth the trouble.

 

[Spook50]

My suggestion:

Run a big fat gauge test wire pair directly from the battery- or better yet, place a charged battery on the tailgate,and wire it directly to the leads of the defrost net and see how it performs.
That test hookup will show you if wiring bigger gauge wire eventually through the body will be worth the trouble.

Not a bad idea. If I can catch it on a frosty morning I can get hit it up and get a good reading of just how much current it SHOULD (ideally) be drawing too without the losses happening wherever they may be in the harness.

 

[OSS]

Just about everything wired through the stock wiring harness takes a big hit with a voltage drop. I guess in order for the bundle to not end up being gigantic, Toyota has to use dinky wires and just accept the resistance.

The cabin fan is a good example. When wired through the stock harness it blows ok. But when wired with 10AWG wire pairs directly to the battery- it blows like a jet engine when on high. Night & day difference.

 

[archtimb]

I will also note to check your defrost switch. When I was looking to repurpose one of the four switches I had accumulated over the years I found all four to be limiting voltage due to corrosion. They can be taken apart and cleaned up.

 

[Spook50]

Just about everything wired through the stock wiring harness takes a big hit with a voltage drop. I guess in order for the bundle to not end up being gigantic, Toyota has to use dinky wires and just accept the resistance.

The cabin fan is a good example. When wired through the stock harness it blows ok. But when wired with 10AWG wire pairs directly to the battery- it blows like a jet engine when on high. Night & day difference.

Boy you ain't kidding! Another reason I'm researching an upgrade for the OEM blower that can still use the factory switch to control a PWM.

In a perfect world I'd love to have a complete modern harness with relays where appropriate so every device has full battery power available.

Years ago I looked into an ISIS (not even sure what they're called anymore) system but the cost both financially and for time were astronomical.