Yes I understand the wiring and it’s function completely, I am an electrical engineer. I have analyzed circuits with 5 million transistors in them for my job and I have been repairing vehicles for 51 years. My company developed the single wire J1850 transceiver chip with Chrysler to move to the buss communication structure used on all modern vehicles today. I am trying to use that knowledge to help you but your fighting me on this diagnosis. As I said, there are two paths to energize the lift gate glass actuator . One of them uses a relay and one of them has no relay. A relay is used when it’s necessary to control a high current load but not pass all that current through the control circuitry, in this case the BCM which decifers the inputs from the remote module, the dash button and various other inputs to decide if the lift gate glass actuator should be energized and then uses a relay to route the current to the load. The other route uses the switch on the back lift gate to open the lift gate glass and does not use a relay because all of the load current can pass through that switch. If that route also results in no voltage to the actuator solenoid then either the relay and it’s wiring from the relay to the actuator is not the problem or there are two different faults which is unlikely.

we can do it your way if you like:

There is no second relay, it’s not necessary

Yes you can Hotwire the lift gate glass actuator solenoid if you like but it won’t help you identify the fault. Take a fused wire from the battery to the solenoid hot wire in the lift gate. You say that the solenoid tested good so it should energize but then we still need to find the fault. It can be a lot of things like say the drivers door switch..

You said power is good to the “button” but I don’t know if you mean the dash button or the rear lift gate button.

You seem determined to analyze this a certain way and don’t prefer my diagnostic approach. I’m just here trying to help people like yourself, if it works better for you I can just post the wiring diagram and let you do your thing.


George

 

I have another idea, lets try this. I have attached a schematic with labels and another copy without that is easier to read.

Lets start with the leg that does not use a relay. Test for 12V at "C" ahead of the Liftgate lock cylinder switch. If yes activate the switch and measure at "D". If yes then go to the drivers door and measure at "E" before the left door lock cylinder switch. If yes then activate and measure at the output of that switch at "F". If yes then activate the rear gate switch again and measure at the input to the liftgate release actuator at "A". Report back.

George

 

Sounds like an interesting job. I'm a retired journeyman mechanic of 35 years. I understand my problem and isolated it to simplify. As I am also disabled getting under the dash is extremely difficult. I could take down the headliner and trace wiring. I know where is another relay panel on the drivers side under the dash that takes a lot of pulling to get out. I was simply trying to find out if there is a second and seperate relay for the hatch actuator because under the hood only has one for the lift glass. What I'm not interested in doing is spending time doing what I've already done to determine what I have already. I was looking for s10 blazer specific information on relay locations as I have only had ZR2s. They are wired differently with tailgates. If you have that knowledge it would be helpful. Respectfully, I need guys that know this vehicle, not an electrical engineer who doesn't. If you can tell me if there is a liftgate relay in the underdash panel before I struggle for an hour to get access it would be great.

 

I have repaired this very problem on my blazer in the past. I have never even seen a ZR2, and I definitely have never repaired the lifgate circuit on a ZR2.. The schematics call out any differences between base Blazers and ZR2 models throughout the electrical diagrams such as for the headlights for this model year. The liftgate schematic shows no difference in this case. Could this be an error or omission, I don't know? The tailgate switch does not show a relay in the schematic and it is not required electrically so it would serve no purpose, and therefore unlikely. I gave you the diagnostic flow for the side that does not use a relay, you can check off any steps already completed. Starting from the fuse end, where does the voltage not appear when you energize the tailgate switch? Did you get to the drivers door switch? BTW, yes there is another relay block under the dash, its the body relay block and its a pain in the *** to get to, a disability would certainly make it even more difficult. There is no relay for this function found there but the circuit flow does pass through that block as shown in the schematic. Christine posted on its location and how to take it apart, maybe she can help you. The good news is that I think shes a chemical engineer, the bad news is that she owns an LS model like me, '99 I think.

If you want me to keep helping you I will, with or without ZR2 experience or even a circuit diagram we can fix your lifgate in a couple of posts. This is a simple problem, unless its the BCM or the class 2 data buss which is involved on the other leg but we can figure that out as well. If it is a hard requirement for you that I have worked on the liftgate circuit and body relay block on a ZR2 then I am not your guy. I won't post again unless you ask for my help specifically, that way another member can chime in if they meet your requirement and I am a hard no. No worries either way, I just want to see you get your truck fixed.

George

 

I just saw your signature and you own a ZR2 and a non ZR2 2000 blazer so now I am completely confused about your resume/experience requirements. My resume as it relates to this problem:

I own a 2002 LS Blazer since new
I have repaired the lift glass circuit in this truck
I have repaired hundreds of vehicles in 51 years
I can diagnose and repair any electrical circuit and certainly this circuit
Unfortunately I am a functional EE, is that a killer defect? You decide.


George

 

I own a ZR2 and restored a half dozen. I also own a 4 door with a "liftgate". ZR2s have a tailgate like 2 door Blazers and many ls 4 doors. The only difference in a ZR2 is an off road package with wider and stronger Axel's and suspension and body lift. Everything including wiring is the same as every other model Blazer.

Back to the issue at hand is that I read in another post that their is a liftgate relay in the relays under the dash in 1997 LIFTGATE models. I'm not sure if you are grasping the difference in the rear openings of the ls Blazers. Some have hand operated tailgates with a glass hatch that is actuator operated. Mine is the liftgate version of the ls blazer that has a hand release and an actuator as well as a seperate lifting glass built into the liftgate. As the liftgate actuator relay is not under the hood with the hatch glass relay it must be elsewhere. As detailed in my original post, both actuators work but NO power is going to them from either the rear button, the dash button, or the fob when pressed according to the meter. The dash button does make the HATCH GLASS relay click when pushed which indicates it's getting power. When I used my ZR2 identical dash button it made no difference. Based on this it leaves the still outstanding question in my original post. Is there a seperate relay for the Liftgate actuator that is seperate from the hatch glass actuator in the lift gate? As it is not in the under hood relay box then is it in the under dash box? The issue of power going to the liftgate and hatch glass within was addressed in my original post. NO. To continue focusing on it seems kind of silly once established. I think you are struggling to understand the different rear gate, hatch door, whatever on the same Blazers. Some are like and SUV and some are like a pick-up with a canopy that operate seperate. All Blazers are the same in 99% of the models and this is my first liftgate so I'm looking for liftgate electrical knowledge here. Otherwise I am well experienced in the s10 Blazers mechanical systems including wiring.

 

This is the liftgate model on my 2000 blazer ls 4 door. Not the same as the tailgate/hatchglass model. The gate and glass both have actuators.

 

I understand all of this and now you have made your question more clear for me.There are two different systems in play here, the power door lock system and the rear lift glass system:

The liftgate function (the locking and unlocking of the entire back lifgate, as a rear door if you will) is part of the power door lock system. This uses input from all of the door switches, remote module, the liftgate cylinder switch, the ignition key alarm switch and the BCM. All of these inputs control three different relays in the body relay block which is under the dash on the left side. The wiring is actually quite busy and takes a minute to grasp. It contains: driver door unlock relay, door lock and door unlock relays, all of which offer a way to energize the actuators in the locking direction and then reverse the voltage polarity to energize in the unlocking direction. You have made it clear that you dont want any debug help but I will caution you that given your desire to avoid this relay block and its nasty access, those relays control multiple "doors" simultaneously so if the liftgate is the only "door" malfunction, a given relay is probably not the problem, there is no dedicated liftgate relay, only a dedicated drivers door unlock relay. Also, if you are unaware of the polarity reversing function then your testing may have issues.

The liftglass actuator (rear glass unlock mechanism) is controlled by two routes: the relay which gets input from the BCM, park brake, wireless receiver, VCM, rear wiper and transfer case if so equipped and a second leg that has no relay: fused power, the lifgate cylinder lock switch, and the driver door switch..

SO to summarize what I think was your question about relays:

No relay for the rear liftglass as controlled by the rear cylinder switch

Yes a relay for the other control methods for the rear lift glass in the UHFB

Three "door" lock relays in the body relay block under the dash but none of them are dedicated to the rear lift gate/rear door function.

Let me know if you need anything else. I can supply wiring diagrams, their explanation, diagnostic help or just go away if you have what you need.

BTW, a '97 has a relay under the dash for the doors and no relays for the liftglass function regardless of if it is a liftgate or endgate model as GM calls it on their wiring diagrams.

I will reiterate that an actuator does not need a relay unless one of three things are true:

The control circuit is low power and the actuator needs significantly more power

Multiple inputs are controlling that actuator

A special function is needed like polarity reversal as is used here for the doors.


George

 

Another thing that may be causing all of this confusion. The big difference electrically between the Liftgate models and the end gate models as GM calls them (tail gate as you called it) is the fact that the Liftgate acts as a fifth or rear door and as such is involved in the power door lock system as I stated in my last post. This is where the relays under the dash come into play. The rear glass or lift glass function is electrically the same in both models. The wiring diagram shows this, a reference to both models using the same circuit. This is also true in the ‘97 model.

Good luck, I hope you get it sorted out.



George

 

I am finally at the correct location to create this wiring diagram of your door locks and dash relays. So here is the last of the story:

Good luck,

George