howdy folks, I think the lock on the tailgate was replaced in the past before I bought it. my key will not work on it. the very same day I order a keyless entry remote, the lock started giving fits. if it's latched and I start the blazer the rear glass lock repeatedly locks and unlocks with no pause
to stop it, I have to open the glass, it cuts it out after 5 seconds
what part do I need to change please, is it a bad actuator?
also if the keyless remote was an option, and if mine is not equipped, did I waste my money on the remote? or did all the blazers in 98 have them new.

 

Hmmmm....this is a drop gate right, not a lift gate? Actually I was not aware that the 2nd Gen Blazers ever had a key lock on the rear gate, thought they were electric only.

Regarding the remote operation...do the doors lock/unlock with the remote?

Is there an aftermarket alarm system installed? If so, this is usually the problem.

 

it is a drop gate. there is no alarm system
I can't program the remote because the back glass problems (it won't go into program mode). I hope to find out after fixing this lock troubles

 

Operation:
All 4 doors and the liftgate get the same lock signal on the same wire from the same relay. All but the drivers door get the same unlock signal on the same wire from the same relay. The drivers door has its own unlock relay so that the remote can unlock only that door with the remote with one/short button press as controlled by the remote, the remote receiver and the BCM. Nothing in the truck sends a command to the liftgate only. The way the system uses the same lock motor to lock and then unlock is to send 12v on tan and ground the gray wire at a given motor and the reverse polarity to go the other way.

Possibilities:
It could be a bad power feed, ground, door switch, relay, BCM, remote module or remote transmitter but it would affect all doors or the drivers door only.

There could be a wiring hack or a short somewhere in the wiring harness on its way to the liftgate motor

Questions:
Is any other door doing the same thing?

Is it literally locking and unlocking or is it trying to do one of those operations continuously?

It only does this if the truck is running but does not do it at rest or if the truck has the ignition on but not started?

Do you mean when you start it or after you put it in gear?

If so equipped your remote module is behind the left side of the dash with three wires (org/org/blk wht).

To really find out what's happening here you need to get a set of voltmeter leads on the tan and gray wires going into the liftgate motor and see if its one polarity all the time, same polarity pulsing or the polarities switching back and forth (true locking and unlocking signals).


George

 

One additional operation point:

There is a pair of splice nodes for both motor wires to the liftgate and two rear doors near the rear doors so if there is a wiring fault it helps to narrow down where it is if:

All doors are doing it
All but the drivers door is doing it
The two rear doors and liftgate are doing it
Only the liftgate is doing it

George

 

After I saw Lannys question I did a deeper dive and discovered that the wiring diagrams for this truck/year have an additional page and together reference a liftgate, liftglass and/or endgate. I also reread your post and you reference the rear tailgate lock and then the rear glass release. Can you describe the set up and what's malfunctioning so I can make sure that I am helping you? There is a separate glass release in the door that is malfunctioning but not the door lock itself? Is there a keyed release back there or only a button?

George

 

If its the liftgate glass and not the door lock then pull the "endgate or liftgate liftglass relay" in the "body bussed electrical center (bbec), behind the left side of the dash near the ic fuse block and see if the problem stops. Given the engine involvement it should because this takes the tbcm and pcm out of the equation and drops the possibilities in half.

George

 

the key goes into the push button.
so after going out and checking if this only happens when the engines runs or the key turned on. I notice it's not an lock/unlock. it's as if the lock process is trying to be performed but failing so starting over again immediately.
It does start this only when latched and when the key is turned on (engine doesn't need to be running)
I just now put my ear up to the tailgate outside and in, but if I'm outside and I can hear the sound/vibration, its coming from in the tailgate to the right of the lock cylinder pictured. or right under the rear wiper
also no doors are giving me trouble and lock unlock fine with the switch on the door except the back drivers side. but I can manually lock/unlock it. but no clicking noises from that one
thanks for y'all helping out

 

So its the glass latch and not the "door" lock? Its the setup where the glass unlatches independently of the door/tailgate/endgate/...?

Does that keyed cylinder also unlatch that glass?

Is it perpetually locked or unlocked?

Try removing the relay and tell me if it stops.

George

 

I got around to mess I g with the blazer and need help finding the relay.
yes the glass is independent of the drop tailgate. The glass must be open to access the tailgate latch on the inside.
the key cylinder does unlatch the glass when you push it in. like a button you would press. When I try to use the key on it , I can't turn it, that makes me think the cylinder was changed.
keeping the above in mind, it seems to stay in sync with the drivers door lock. For the perpetual lock ?
can you point or circle the relay on the PIC I have here?

I was looking at that fuse box and none seem to handle locks or rear lift gate.
thanks for any help