Liftgate Release (Hatch lock) failure trouble-shooting

[DPDISXR4Ti]

3/87 built car (early '88 in North America) Rear hatch usually stays locked when doors are unlocked, requiring separate unlocking with key (the problem) rather than being able to simply push button to activate latch solenoid. Note, the Scorpio functions differently from the XR, which was the first thing I needed to understand.

Diagnostic step one was testing the latch solenoid by applying 12V directly. The solenoid activates as it should.

Step 2 was disconnecting the Liftgate Lock Switch (Liftgate Release Switch in '88 EVTM) and testing it's function. It works as it should - resistance goes from infinity to zero when button is pushed.

Step 3 was checking for the presence of power at the Liftgate Lock Switch. I'm seeing 12.08V. A little low, indicating a voltage drop somewhere, but I think the circuit would still fuuction.

Step 4 was electrically disconnecting the latch solenoid and monitoring the voltage change at the connectors as the Liftgate Lock Switch is depressed. No change at all. Zero volts always. Even tried a few different ground points with no voltage to be found.

I have some next steps planned, but figured I'd document this as I'm doing it.

Side note.... The language in the 1988 EVTM (page 144) is very different from the 1989 version (page 123), even though the circuit is identical. The 1989 version makes more sense.

[brokencase]

Step 5 - Relay or dirty socket contacts to relay?

[Ed Lijewski]

Seems you verified power at the liftgate lock switch, verified that solenoid actuates when given power separately, but when both are connected and the switch is depressed the solenoid doesn't operate.

So even with the switch seemingly testing OK (for on/off ohms) the switch itself may be the issue.

YMMV

[DPDISXR4Ti]

Step 5 - Relay or dirty socket contacts to relay?

I think I was testing that about the time you were typing it! I verified the same 12.08 volts at pin 87 with the relay removed. Swapped the relay out with the known-good one next door (gas filler door release), and no change. Freshened up the relay contacts with some contact cleaner. No change. 30A fuse in position 9 looked okay but I tried another one any way. No change.

Ground G1010 verified as good first-hand. Ground G1005 verified as good via reference since it is shared with the RH front door lock switch which works fine. That concludes all the "Troubleshooting Hints" in the EVTM.

[DPDISXR4Ti]

Seems you verified power at the liftgate lock switch, verified that solenoid actuates when given power separately, but when both are connected and the switch is depressed the solenoid doesn't operate.

Correct

So even with the switch seemingly testing OK (for on/off ohms) the switch itself may be the issue.

I was pondering something like that when I noticed that it seemed the one on the '89 parts car is a little different (upgraded?) from the '87. But I couldn't wrap my head around how it could be possible. It's either lets the juice through or it doesn't, right?

[Ed Lijewski]

Can't remember specific examples ATM but I've encountered a few electrical items (on cars or elsewhere) that ohmed OK but didn't operate as designed.

Since you have an '89 parts car, swapping one from it is worth trying.

YMMV

[DPDISXR4Ti]

Since you have an '89 parts car, swapping one from it is worth trying.

Except it's pooched from having been broken into, or so it would appear. Figures, I had access to 9 parts Scorpios this Fall and didn't grab one of these.

[Ed Lijewski]

Re Ohming/resistance switch testing. Infinity reading = a gap between metal contacts. Any reading of resistance = at least some metal contact, but not necessarily proof that necessary amount of current for operation of device can flow at that contact.

Try hot wiring or jumping the switch contacts.

YMMV

[brokencase]

It seems that you have verified everything. It should work.
Is it perhaps some mechanical issue...Like the solenoid is operating but is unable to pop the release?

The only other thing would be that the door lock switch is not working as reliably as you think.

Unscrew the weather sealed door harness connector (near the hinges) on the driver's door.
Separate the connectors and spray contact cleaner on the contacts.

Not a bad idea to to this on all the connectors on all the doors. After 30 years the contacts can get a little chalky.

I can't think of anything else.

[Ed Lijewski]

'89 S.M.: With doors unlocked, when button is pushed it should depress microswitch which then powers the solenoid. So if you have the liftgate underpanel off to see what takes place, when depressing the button that should depress the microswitch sufficiently to power the solenoid. If it doesn't, either a) the button is not depressing, or b) the microswitch is faulty.

YMMV

[DPDISXR4Ti]

Fixed! I realized I had one more test to conduct, surprised I hadn't already thought of it. I disconnected the quick-connector for the switch and shorted the now exposed contact points. Bam, the latch opened! That confirmed to me that everything else in the circuit was good, and it HAD to be the switch.

Going with Ed's idea that the switch could Ohm-out okay but perhaps still not function, I went and took another look at the buggered assembly removed from the '89 parts car. In short order, I realized that the microswitch could be removed, and once removed and connected to the harness, it fired the solenoid open at will.

Out came the microswitch from the hatch, and before putting the one in from the '89, I took the pic below showing how the part was upgraded with a longer, metal piston rather than the plastic one on the '87.

Once installed, everything works as it should. The end.

HatchLockSwitch.JPG (1.04 MiB) Viewed 8139 times

[Ed Lijewski]

Metal vs. Plastic rod is insignificant; I'll bet that XR and Scorpio door microswitches have plastic rods or buttons. What likely matters most is whether the internal activation point is different between the two.

YMMV

[Ed Lijewski]

On second look at the photo above, comparing the early switch's boss for the actuator rod with the later switch without any boss, it's possible that the boss could limit the plastic rod from fully or always completing its required travel.

YMMV

[john keefe]

I've had this problem from Day 1, though it's an earlier Scorpio. I don't have a button to release the trunk from the interior. AFAIK, it's switched with the door key. Where would the trunk switch be located on the later models?

[DPDISXR4Ti]

I've had this problem from Day 1, though it's an earlier Scorpio. I don't have a button to release the trunk from the interior. AFAIK, it's switched with the door key. Where would the trunk switch be located on the later models?

Nothing has changed in how the circuit works. The MANUAL changed in how they describe the circuit operation. The switch itself, which is part of the push-button/lock assembly, appears to have been upgraded - it's is changed out pretty easily. Contact Jeff Herson - I bet he has one from a '89.