GKK

I recently replaced the hatch struts on my 91 Vette and now the defogger does not work. (Defogger worked fine before)

I noticed the new struts have a shorter defogger tab which did not fit the connector as tight as the old struts did so, I replaced the ends with a better connector and now would like to know how to check each strut connector with my digital voltmeter.

I've read several posts that say to check each strut connector by connecting the voltmeter ground to the body and the positive side to each of the four strut connections. Some say to check it in Ohms and others say to check in Volts?...

What should the voltage or Ohm readings be at each strut connector?

Thanks

GKK

I connected the negative voltmeter lead to the bottom drivers side strut connector and the positive voltmeter lead to the bottom passenger side strut connector and found the voltage to be 14volts with the defroster button on.

Does that mean there is voltage going across the defroster grid?

ccrazor

You can check it with either volts or ohms.. To check volts, put meter on the right and left feeds, you should get 12v. Leave one meter lead connected and put the other on the connector to the defrost grid, s/b 12v again, also at the other end of the grid.. Similarly if you use ohms you should get 0 ohms ( grid is about .5 ohms) from one side to the other. (key off)

ccrazor

No that just means you are getting power that far, check at each end of the grid..

GKK

So, with the Defrost button "On", all four strut connections should read?...

Passenger side bottom____volts
Passenger side top____volts

Driver side bottom____volts
Driver side top____volts

Thanks for your help.

ccrazor

The grid s/b connected one end to each upper end of the struts..

GKK

OK here's what I found...

With the Defrost Button "On".

Passenger side bottom connection_14_volts
Passenger side top connection_14_volts

Driver side top connection_14_volts
Driver side bottom connection_0_volts

ccrazor

Where is the other lead connected for these tests mainly the last? If to a ground disconnect the bottom driver side connector and you should get 14v. Try an ohm test on each strut top to bottom key off s/b 0 ohms..

GKK

The lead is connected to a body ground.

When I removed the bottom driver side connector, the voltmeter reading was erratic.

Does that mean the strut connection is bad? Maybe I can solder the bottom driver side tab to the strut to make the connection better.

It sounds like the driver side strut grid connection isn't letting the voltage through to the bottom connection.

ccrazor

I would see if you can return the driver side strut for a replacement..

GKK

The Ohm test measured...

Grounded to the body, Key Off.

Passenger side bottom_10.5_Ohms
Passenger side top_10.5_Ohms

Driver side top_10.8_Ohms
Driver side bottom_1.6_Ohms.

csthews

But I would disconnect everything first. You may already know this, but just in case: You are checking continuity across the grid. Make sure your meter is working properly by touching the two leads together. It should drop to zero with the leads touching (zero resistance or continuity). Next, disconnect the leads from the struts and check across the grid. Disconnecting may not be necessary with the ignition off, but it doesn't hurt.

GKK

I found that the driver side strut's top defrost connection, was tightened over paint which wouldn't let the current through to the bottom connection.

I scraped the paint off and reconnected everything. Now, both bottom connections get hot with the Defrost button On and the glass feels warm.

Cliff Harris

One thing that wasn't mentioned is to check for continuity through the struts themselves. There needs to be a connection from the top terminal to the bottom terminal. That seems to be the problem that was solved in the previous post.

There should be low resistance (ohms) from top to bottom.

If you're measuring voltage with the defroster on, it should be nearly the same at the top and the bottom (referenced to ground).

ccrazor

If you read post #8, I stated to check each strut top to bottom for 0 ohms.. Nice to hear it was a simple fix..