by Bob Beranek
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Recently we’ve seen an increase in questions on the Auto Glass Safety Council (AGSC) Master Certification and requests for more study materials for the exam. Master certification is different from the Technician or General exam because it tests more advanced services usually offered by the full-service auto glass shops. These services can include:

  • An in depth understanding of regulations and standards pertaining to our industry,
  • Safety related issues and OSHA regulations for the work place,
  • Laminated glass fabrication (glass cutting and finishing),
  • Pattern-making and template construction,
  • Older and more unique vehicle glass replacement, and
  • Understanding electrical circuits and troubleshooting those circuits.

Though information on some of these subjects is harder to find than others, I thought I would begin this series of “Master” posts with the most common electrical problem a glass shops see – rear window defroster malfunction.

There are three defroster malfunctions that present themselves to the customer; either the defroster does not work at all, one or more gridlines do not work, or the defroster connectors come off. Let’s address each of these.

  1. If the defroster does not work at all, it means that power is not getting to the unit. First, you should check the fuse. If the fuse is blown, replace it and make a suggestion to the owner that they get the system checked by the dealer. A blown fuse means there’s something wrong with the system. The system (circuit) consists of:
  • The power source (battery),
  • The wiring from the battery to the fuse block,
  • The wiring to the switch,
  • The wiring from the switch to the connectors on the defroster,
  • The connectors on the defroster both the incoming power and the ground, and
  • The defroster grid itself (Unit).

Replacing the fuse is a short-term fix.  If you’re able to trace the problem to its source, do so. However, if you do not have the expertise to diagnose and fix the problem’s cause, I suggest you refer the customer back to the dealer.

Photo Courtesy Main Image – Ebay


  1. The customer comes in and complains that one or more of the lines are not working. This usually indicates that the grid line(s) is severed and must be repaired.

How do you find the break in the lines and how do you fix it?

You will need a defroster repair kit from your local hardware or auto parts store. It will consist of a small jar of metallic paint, a brush and a template. You’ll need an ohmmeter, which uses an outside source of power for its reading, not a test light. A test light uses the power supplied in the circuit to light the bulb in the tool.  This adds another unit to the circuit and could confuse the internal computer of the added unit and cause further problems.

Turn the vehicle on and connect the ground lead of the ohmmeter to the defroster’s ground connector, this is usually on the passenger side of the back glass. Now take the power lead and gently drag the lead along the suspected grid line. A properly operating grid line would have a slowly decreasing volt reading from 12 volts to 0 as you move the lead from power side to ground side. A broken line would have a consistent 12 volt reading until it suddenly drops to 0. When the voltage drops to zero suddenly, that is where the break in the line is located. Mark the break point and attach the template to its location. Then paint a “bridge” across the two ends of the line with the metallic paint and allow to dry thoroughly. Retest and confirm repair.

  1. The connector tabs frequently break off of the bus bars due to cleaning the inside surface of the back glass or from items stored on the back shelf or storage area. There are several products that do an excellent job of reattaching the tabs and reestablishing the electrical circuit. However, there’s another way that has proven results.

You can simply use a cyanoacrylate glue, such as Super Glue, to reattach the connectors to the glass surface at the point of separation. Then use the defroster metallic paint to make the electrical connection between all circuit components. The circuit components are the connector, the bus bar above the separation point, and the bus bar below the separation point. This will join all of the components and reestablishes the circuit. Then allow the metallic paint to dry thoroughly and test the repair.

Caution:  Do not add concentrated heat to a particular point, such as a solder gun. This could cause a thermal break.

I’ll give you more information concerning the tested knowledge in The AGSC Master’s Certification exam in future posts. My “Lost Arts” series of posts cover the laminated glass fabrication and finishing and can also help when studying for the exam. Please contact me if you have any other questions about Master Certification.


As glass technicians, what are our responsibilities when replacing tinted glass? Does aftermarket tinting of automotive glass violate the National Traffic and Motor Vehicle Safety Act of 1966 (NTMVS)? Being a student and fan of research, I decided to investigate this issue.

The Federal Motor Vehicle Safety Standard 205, through adoption of ANSI Z26.1 standard for automotive safety glass, dictates automotive safety glass must have 70 percent light transmittance (LT) in the front and side windows. That seems straightforward. However, can the side windows be tinted darker than that directive?

First the facts.

Federal Motor Vehicle Safety Standard

S5.1 – “Glazing materials for use in motor vehicles must conform to ANSI/SAE Z26.1-1996…”

ANSI Z26.1

5.2.3 – “…Safety glazing materials or multiple glazed units intended for use at levels requisite for driving visibility in the motor vehicle shall show regular (parallel) luminous transmittance of not less than 70% of the light, at normal incidence, …”

National Traffic and Motor Vehicle Safety Act of 1966

30122, (b) A manufacturer, distributor, dealer, or motor vehicle repair business may not knowingly make inoperative any part of a device or element of design installed on or in a motor vehicle or motor vehicle equipment in compliance with an applicable motor vehicle safety standard prescribed under this chapter unless the manufacturer, distributor, dealer, or repair business reasonably believes the vehicle or equipment will not be used (except for testing or a similar purpose during maintenance or repair) when the device or element is inoperative.”

We all have seen side glass tinted beyond the 70 percent LT in the federal standard. Does that mean the aftermarket tinting of glass violates the law? There is a loophole.

The government allows vehicle owners to customize their vehicle in the way they see fit and gives regulation of the customization to the states. For example, a person can paint their car a different color, add a sun visor to the top of a truck, or tint its glass. However, the Federal government will not allow the “repair” business to customize a safety device manufactured into the vehicle.

The Federal government has a definition of a repair facility.

30122, (a) “In this section, ‘‘motor vehicle repair business’’ means a person holding itself out to the public to repair for compensation a motor vehicle or motor vehicle equipment.”

The key words here are “repair business.” An aftermarket tinting company offers a product for customization not for “repair”. They don’t repair the glass by tinting it, they add tinting film as an add-on customization.

Therefore, adding tint to glass is allowed by the absence of federal regulations against it. The only limitation on the “customizers,” or tinting professionals, is the percentage of light transmittance allowed by the state, which is regulated when the vehicle is sold. To make things more challenging, each state’s regulations are different.

What does this have to do with the glass replacement company? An auto glass replacement company is a repair facility according to the federal definition of the word. However, aftermarket tinting added to the glass after it’s replaced, is a customization that must follow state laws which regulate aftermarket tinting. If a replacement company tints the glass either as an added service after the replacement or subcontracts a tinting company to add tinting after the replacement, the replacement company must require all state laws be followed. If not, the repair facility (replacement company) that contracted the work could be held liable.

I am not an attorney. These observations are based on the study of regulations available to the public. However, I reached out to the National Highway and Traffic Safety Administration to see if it could answer this question definitively and I will let you know what they say. In the meantime, make sure you know your state’s laws concerning acceptable tinting guidelines.

Last November I posted an article on the contents of a Vehicle Identification Number (VIN). I explained the digits used to identify an automobile and detailed what information the VIN did (and did not) contain. Recently however, I have heard people in the industry tell me that they have a VIN decoder that picks out the right windshield for a vehicle. In my experience, the decoders may not complete the assignment.

It’s true, knowing the complete VIN can shorten the list of windshield options you have to choose from, but it doesn’t necessarily pick the part for you. Let’s take the Jeep Cherokee as it has 51 windshield options. Last week I conducted a training course where we had to replace a 2015 Jeep Cherokee windshield. When we typed the VIN into the decoder on my software, it gave us over 20 windshields to choose from. 

On the same day, we had a Ford F150 that gave us the part we needed via a VIN decoder, so they aren’t useless. However having a decoder will not give you all of the information you need for all vehicles. You may have to contact the dealer.

How can a dealer know what glass is in the vehicle by the VIN and we can’t? It’s because they have access to what is called the “build sheet.” The build sheet is the actual information of what was included in the vehicle at the time of assembly. The VIN does not include the glass part number, but the build sheet does. With this proprietary information the dealer can tell you exactly what glass was put into the vehicle. But will they?

Some software companies have told me that they draw their information from build sheets, which is great. However most still admit they don’t have all of the information required for all makes and models. Some dealerships are happy to help, but it’s to the carmakers/dealers advantage to keep some things to themselves rather than releasing all of the information they have available. If all specifications and information were made public, the carmakers’ dealer base would be undercut and beaten at every turn.

The reality is professional questioning of the customer is still important in having the right windshield for the job. A significant skill of any customer service representative (CSR), technician or owner is the ability to lead the customer through a series of questions that will pare down the information necessary to pick the correct part. If there’s something related to the glass that can’t be seen, heard or experienced by the customer, then the professional CSR can ask about other options that will lead them to features that would differentiate a glass part. For example, if a vehicle has a heated mirror, then it is likely that it would have a wiper park heater as well. 

I have an idea. What if we help our fellow auto glass professionals and send in hints on questions to ask the customer that narrows down the windshield options? Make sure the hints are correct before sharing them. Send them as a comment to this post, I know this would be greatly appreciated and a big help to everyone.  I’ll even bet that the more you give, the more you will receive in new information.