Using MG Chemicals Electrically Conductive Adhesive
With winter fast approaching, it’s time to get the mitts and scarves out, and make sure your rear defroster is ready too. If your rear window isn’t clearing frost properly or at all, don’t panic. The problem is often due to a broken electrical connection or damaged grid line in the defroster, and you can fix it yourself. Using MG Chemicals 8331D Silver Conductive Adhesive and a few basic materials, you can repair these electrical connections with a simple “cold solder” method, restoring the defroster function without replacing the glass.
What You’ll Need for a Rear Defroster Repair
Let’s get started, here’s a list of what you’ll need:
- MG Chemicals 8331D Silver Conductive Adhesive – we recommend this electrically conductive adhesive (ECA) due to its fast working time, high electrical conductivity, and resistance to humidity, saltwater, and aliphatic hydrocarbons (found in fuels), making it well suited for an automotive repair.
- MG Chemicals 409B Electrosolve Contact Cleaner – for cleaning electrical connections.
- Safe on many plastics
- Zero residue
- MG Chemicals 824 99.9% Isopropyl Alcohol – for general cleaning.
- Safe on most plastics
- Zero residue
- Fast-drying
- Applicator and mixing supplies
- Disposable mixing surface
- Disposable utensils to mix and apply with (like a Q-tip, swab or toothpick)
- Flat putty knife (for repairing grid lines)
- Tape: masking and general purpose – to mask off the area for a clean and professional repair and hold a broken tab in place.
- Multimeter or 12 V automotive test light – for locating breaks in electrical continuity and testing the repair.
- Hand tools – if a connector tab has broken off, then you may need small pliers, tweezers, or a small plastic clamp (as to not damage the window).
- PPE – Safety goggles (always) and disposable gloves (nitrile or latex).
- Old or work clothes – epoxy is impossible to remove from clothing once cured.
- Warm weather – it’s best to do this repair when the temperatures outside are close to room temperature. Cold temperatures may interfere with the curing process.
A Word about Safety
- Electrical safety: ensure the rear defroster is turned off and the battery is disconnected before starting any work.
- Damage to Glass: be gentle working around the rear window.
- Do not attempt to solder a broken connector back on to the window with a flame, heat gun, or soldering iron. The high amount of heat can crack the window.
- If old adhesive needs to be removed, do not scratch the glass, just the metallic surfaces. You can use the masking tape to help protect areas while sanding.
Repair Guide
Broken Connector Tab
Inspection
It might not be obvious at first that a connector tab is broken, so start by gently unplugging the wires that connect the defroster to the vehicle. Inspect the tabs and connector for wear, damage, or corrosion and check for continuity. If they are intact but corroded or dirty, clean with electronics cleaner and light sanding if needed. Electronics cleaner like MG Chemicals 409B Electrosolve Contact Cleaner is safe for many plastics and leaves zero residue.
Don’t forget to ensure the battery is disconnected before moving forward!
Clean
If a tab is broken, you can fix it using our DIY rear defroster repair. Start by cleaning the repair area with MG Chemicals 824. This 99.9% pure isopropyl alcohol is safe for plastics and paint. Its high purity will ensure that no residue is left behind that could interfere with bond and electrical connection. Clean both the tab and the window side.
Mask
Using the masking tape, mask off an area around the repair that you want to protect from accidentally getting epoxy on.
Prepare Epoxy
If it’s cold outside, you may want to slightly heat the repair area with a hair dryer so that it is lukewarm to the touch. Do not overheat, as this could crack the glass.
On a clean disposable mixing surface, dispense equal parts of 8331D. With a disposable utensil, mix both parts together thoroughly. Place the caps back on the syringes to keep the product fresh. You may choose to use a plastic clamp, tape or tweezers to hold the broken connector in place at this point but be sure that you’re still able to access the area where the epoxy will be applied.
Apply
With a small disposable utensil, apply the product to the broken tab. Place epoxy on both the tab and the repair area. Ensure the tab is reinstalled into its original position.
After 20 minutes, you can mix more epoxy and apply another layer as needed. If you’re building up layers to reinforce the repair, ensure that it’s not going to prevent the tab from being fully inserted into its electrical connector.
Avoid the temptation to test the repair right away. 8331D will cure in 6 hours at room temperature. However, we recommend letting it sit for 24 hours before reinstalling the electrical connector.
Note that epoxy will take longer to cure in cold ambient temperatures, but you can use a hair dryer to gently warm the area.
After 24 hours, inspect and test continuity of the repaired tab. If all is good, remove the masking tape, gently reconnect the electrical connector/battery and test the defroster.
The epoxy will cure to a hard and conductive state. If that didn’t happen for you, see our troubleshooting tips at the end.
Broken Grid Lines
Locate the break
If the connectors are fine but some grid lines are damaged, this DIY rear defroster repair process works for that too. Often, a break here won’t be obvious to the naked eye, so it’s best to work in an organized and methodical fashion. Grab the test light or multimeter and attach it to an unpainted metal part of the car (like the rear door striker). From the inside of the car, start touching the positive lead to each grid line (from the top down) and take note of which have power and which do not. If using a multimeter, check for voltage.
Note: on North American cars, the positive side of the defroster is usually the driver’s side, but you should confirm by checking both sides for 12 V against ground.
Test each line
Starting at the positive side of the grid line, slowly move the probe laterally along each individual broken line (towards the negative side). This will help give us a rough idea of where along the line the break is. Mark the break with a small piece of tape. Disconnect the battery before moving on to the next step.
Clean
Start by cleaning the area with MG Chemicals 824. This 99.9% pure isopropyl alcohol is safe for plastics and paint. Its high purity will ensure that no residue is left behind that could interfere with bond and electrical connection. Clean the repair area on the inside of the window.
Mask
Mask off an area around the break roughly the same width as the original grid line. The goal is to use this as a template, so that you can make a clean and professional repair.
Prepare epoxy
If it is cold outside, you may want to warm the repair area with a hair dryer so that is lukewarm to the touch. Do not overheat, as this could crack the glass.
On a clean disposable mixing surface, dispense equal parts of 8331D. With a disposable stick, mix both parts together thoroughly. Place the caps back on the syringes.
Apply
With the flat putty knife, apply a thin layer of the adhesive to the template, ensuring it overlaps slightly on the grid lines on either side of the break as well. Ensure the applied amount is uniform with no gaps. Flatten it down into an even layer.
Note: epoxy will take longer to cure in cold ambient temperatures, but you can use a hairdryer to gently warm the area.
After 24 hours, inspect and test continuity of the repaired grid lines. If all is good, then remove the masking tape, reconnect your battery and turn on the defroster to test the repair.
The epoxy will cure to a hard and conductive state. If that didn’t happen for you, see our troubleshooting tips below.
Troubleshooting the Repair
- The epoxy didn’t fully cure
- Incorrect mix ratio – carefully remove epoxy and try again
- Parts A and B were not mixed properly – carefully remove the epoxy and try again
- Ambient temperature was too cold – gently heat the repair area with a hair dryer. If it is really cold outside, wait for warmer weather.
- Epoxy is fully cured, but the line/defroster is still not heating
- Check integrity of the repair. Even a small gap between electrical parts can prevent sufficient connection. Repeat the repair process and ensure full coverage.
- The defroster is heating unevenly
- Hotter parts indicate a higher resistance. If the adhesive was applied there, then it may have been applied too thin or the electrical contact is not sufficient. 8331D will cure to a highly conductive state; repeat the repair process and ensure adequate coverage. Apply enough adhesive so that it also makes contact with a good part of the line as well.
|
Symptom |
Likely Cause |
Fix |
|---|---|---|
|
Indicator light on, but entire grid not heating |
Blown fuse or broken tab |
Replace fuse or reattach tab with 8331D |
|
Defroster works in some but not all areas |
Broken grid line(s) |
Repair with ECA |
|
Tab repair not heating |
Insufficient coverage |
Re-clean and reapply with epoxy |
|
Uneven heating after repair
|
Thin adhesive layer |
Add more adhesive for better conductivity |
|
Epoxy not fully cured |
Improper mixing, or Ambient temperature too cold |
Try again but ensure 1:1 mix ratio, and mix thoroughly for a longer period of time Warm the repair area with a hair dryer or wait for warmer weather |
