: How to test your trunk pull-down motor

03-08-07, 11:00 PM
My first how-to, so bear with me.. I also don't have pics, so I'll try to explain as clearly as possible. If you ever want to test to ensure your trunk pull-down motor works (the one I tested was on a '93 STS), here's how to do it.

Note - I tested mine with the unit out of car, and wire cut and exposed.

The unit is comprised basically of two components; the switch and the motor. You'll need the following tools to test the thing out:

1. Torx screwdriver (two sizes, not sure which ones, sorry)
2. Small open ended wrench (7/16 works fine)
3. Source of power - either a car battery, or better yet an AC to DC adapter (I used a 9V DC adapter)
4. Voltage meter - not necessary, but helps

Start by testing the motor.
First, remove the switch unit. There is a small torx screw that has to be removed to free it up. I noticed it was still held in place by the latch piece that holds the trunk, so I also had to really loosen up the two bolts that hold the metal plate to the plastic. Once there was enough play, the switch will come right off.
You'll notice at this point two small metal tab connections for current where the switch fed power to the motor. To test the motor, simply put your negative and positive from the battery or adapter to the two metal tabs. The motor should whir to live and the latch should either move up or down, depending on the polarity of your connection. If nothing happens, you know your motor has a problem. As a side note, you can further take the motor apart and clean the brushes and whatever, that may help.

Next thing to do is test the switch - I'll explain the way I did it with the voltage meter. First, know which wires are which:

Black wire: negative/ground
Black w/ stripe: constant power
Red wire: power signal from computer

To test the switch (while the switch is disconnected), first connect your ground/negative to the black wire. Then, connect your positive to both the black wire with the stripe and the red wire at the same time. Now, look on the switch and find the two small metal clips that supply the power to the motor. With everything hooked up and the switch open (not pressed), place the leads of your meter to those two small connections on the switch. Your meter should give a reading of 12V, or whatever your adapter puts out. If you press the switch at this point, it should kill the flow of power; this is because the switch is only pressed once the trunk is fully closed.

Finally.. time to test the unit as a whole. If it's apart, put the switch back onto the body/motor, it goes the reverse of removal. May be a little tricky, but you'll get it.
Hook up your power supply to the wires; your negative/ground to the black wire, and your positive to the black striped wire - this time though, leave the red wire coming off the switch alone.
With everything hooked up and your power live, take the red wire and touch it to the positive and black striped wire connection, making sure that the switch is also open; the motor should come to life. If you hit the switch, it should kill it as before.

If something isn't working right, double check any connections between the switch and the motor.. there really isn't much to it without the computer involved. If I'm leaving anything else, let me know. Hope this helps!

03-14-07, 06:59 PM
very good.
but one thing. . if its in your car and you shut your trunk and it goes down/ then why would you test it ?? because it works.

03-16-07, 02:58 PM
What he said... just shut the trunk.

Unless you just bought one off eBay or something?

04-06-07, 11:05 AM
Well if it works, you don't need to test it,

But if it doesn't work, this allows you to isolate the unit from the rest of the electrical system when troubleshooting, and further allows you to isolate both the motor / switch.

Tommy Deville
04-11-07, 04:32 AM
I believe that you can run the "test" though the OBD2

12-09-10, 10:53 AM
I realize this is a very old post, but it sure did tell me what I needed to know!

I don't understand why anyone who has a working motor would respond to your post or even read it. The title alone tells everyone it is a TEST, and there is never any reason to test something that works (unless you're just bored and need to kill time).

My motor isn't working, and I was back there messing around with a test light but never got around to hooking up voltage to it. I did show constant voltage in the red wire and on/off voltage in the black/white wire depending on switch position. So, that tells me that the switch is working most likely. I do know one thing: my trunk release button pops the trunk. It's just that the pull-down motor doesn't do anything, which requires me to always slam the trunk! And since the trunk lid is a bit heavier than (for example) a 72 Ford Maverick or something, it takes a little more of a slam to get it to latch. Also, I believe part of it is because it's so much more well sealed and air tight than non-Cadillacs (I'm guessing).

So anyway, I do appreciate your post and will certainly try this! I always have a 20-foot length of speaker wire I use for tests like this. I have a roach clip (oh, sorry, 70's flashback... Alligator Clip!) hooked to one end of each wire. I use them to clip to my car battery's positive & negative. Works awesome! This is better assurance I'm getting a good ground, plus I don't have to hold a piece of wire to metal and wonder if it's getting a ground.

Thanks again! :worship:

I'll let you know what I find out!:hmm:

10-29-11, 07:36 PM
Ok, everything looks good with this process, but is there any change to the process if the little lever on the front side of the switch away from the connector either up or down? My switch voltage seems correct across and stops when the trunk is closed or the switch depressed, but can't seem to have any different when the front lever is either up or down. Does this lever do anything?82190

12-02-11, 04:29 PM
yes, that little lever on the front shuts off power to the motor when the lid is closed. My problem is the motor runs fine to close, the button releases the trunk fine, but it wont go on to raise the latch again after it opens. Anyone with any ideas? Oh, and I have the four wire plug not the three wire plug.

12-03-11, 11:51 AM
And if you can't fix it, can't find and/or afford a replacement motor or switch, and just need to close the truck tighter, you can disconnect the power, take the assembly apart, screw/turn the latch hoop down a few turns, then re-assemble and reattach. You may have to do it once or twice to get the truck lid down to it's normal position, but the electric release will still work fine to pop the trunk, until you can replace the screw motor. :)


03-03-12, 08:46 AM
I bought an eldorado that already had the motor removed from the clear trunk latch mount. I just bought a new motor, but the connector I have to hook into that motor doesn't fit. The motor looks like it takes a two-prong but the wires have a flat female 5-prong connector. Is there an adapter or something I'm supposed to have?
Thank you!

02-16-16, 01:31 PM
That is what happened to ours. I used dry graphite powder last summer and for a while it would open and the latch would raise back up but this winter after not using the trunk in a long time, it opened but the latch stayed down. I clicked and clicked the remote and pulled on the latch and after several times pulling on it it raised, almost but not quite all the way back up. Since it is now frozen in an up position I can only close the lid manually and there is a gap around the entire perimeter of the trunk lid by about the thickness of an index finger. I have to go buy a new pull down motor and hopefully I can replace it myself. Only problem with that is, after removing the 4 plastic screw caps and pulling up on the shroud the edge is connected to the rubber gasket that lines the front bottom edge of the trunk compartment. It appears I might have to use a screwdriver to pry up on it to get it loose so I can get at the motor.