850 sedan trunk lock testing question.

Post by **scot850** » 09 Jul 2016, 10:43

The project 850 has an issue with the trunk solenoid not working (I'm assuming it has one as my 93 GLT did). When locking/un-locking the doors with the fob, the trunk lock does not actuate in either direction. Auto electrics are not my forte (merely a mechanical engineer), so how do you test it for power getting to the lock? Is the power there all the time or only when the lock is activated with the fob?

Is there a particular wire I need to check for power?

Appreciate the help.

Neil.

Post by **scot850** » 09 Jul 2016, 15:29

None the wiser after looking at the wiring diagrams. I'm assuming I use the diagram for the 4 door, and as I have to press the fob once to open the driver door only and a 2nd time to open the other locks, I'm assuming I have the 2 stage lock system?

I identified which component (3/78) is the trunk lock mechanism and it has 6 (?) wires running from it.

Terminal # 2 + #8 = SB wire (Solid Black?) which are the ground/earths with #2 and #8 linked

Terminal #4 = Y/GR (Yellow/Green?) which appears to send the signal to lock the trunk

Terminal # 5 = GN-BN (Green/Brown?) which appears to run to the Central Locking relay

Terminal # 6 = Y-BN (Yellow/Brown) which I'm not sure where it goes. Is this a constant live?

Terminal # 7 = Y (Yellow?) again this looks like it runs to the Central Locking module.

What I can't figure out is there a constant live feed I can check for and if so what wire is it, and if there is no live feed, do I have to have someone activating the lock using the fob to check for a live signal?

Thanks,

Neil.

Post by **scot850** » 09 Jul 2016, 16:30

I have more info to add if it helps. It may or may not be relevant.

I decided (thunderstorm outside so no yard-work for a while) to have a quick look at the rear of the sedan and thought that if the licence plate lights work maybe the earth may be good. Not a 100% correct assumption I know, but worth a shot. Well the licence plate lights would appear to work (or one did) after replacing a failed bulb. So the earth/ground should be good but I'll check anyway when I find it. What I did find was the lock for the gas flap is not working either. These both have a commons wire feed to them, but not sure where the feed links. I'll have to try and follow these wires. One wire is a Yellow/Brown and the other is a Yellow. The yellow goes to a connection pin #2 on the trunk lock marked 'M-' and the Yellow-Brown comes from the 'M+' Pin #6 on the trunk lock.

Is there something that is 'common' that may affect the operation of both items that may not be related to a broken wire in the trunk lid hinge, as the wires to the fuel tank lock are not run through there? I suppose both items could have failed and for possibly different reasons. I think the lock for the fuel flap is easy enough to remove so I could feed a direct 12V to is to see if that actuated it (it is 12V isn't it?). If it works then power may not be getting to either.

I'm assuming all the locks would be fed from the same fuse?

Help would be appreciated.

Neil.

Post by **scot850** » 09 Jul 2016, 17:04

Again may not be of relevance, but with all the door locks locked (but not the trunk) when I opened the trunk lid the alarm horn went off.

Can the alarm horn be adjusted/cleaned. Sounded pathetic!

Neil.

Post by **scot850** » 10 Jul 2016, 17:38

No electrical geniuses out there that can point me in the right direction on this challenge?

Neil.

Post by **MadeInJapan** » 10 Jul 2016, 22:17

Those alarms get pitiful... Mine is pretty much non-existent...sounds like a pip squeak. Anyway, best I can say on the alarm is grab one from a junker...but it might be the same too... I wish I knew about electrical issues to help you but that's my greatest weakness on these cars.

Teddy1975 · Post by **Teddy1975** » 11 Jul 2016, 02:26

I looked into how the door lock actuators work when I put in an after market alarm in my 96 850.

The voltage on the actuator wires for the trunk are like this:
Idle: Earth/Ground on both Yellow and Yellow-Brown wires.
Lock: +12v on Yellow-Brown wire, Earth/Ground on Yellow wire for ~0.7 seconds.
Unlock: +12v on Yellow wire, Earth/Ground on Yellow-Brown wire for ~0.7 seconds.

Green-Brown, Yellow-Gray and Black(Ground) wires are for the lock position sender to the central locking relay.

Blue-Brown is for the interior light, will be shorted to Ground(Black) when trunk is open.

Since the voltage will only be on for such a short while, a digital voltmeter may not respond quickly enough to show the true voltage.

Also, check if you have locked the trunk using the key and not fob. When trunk is locked manually, the key should be removed in vertical position. If not, trunk will not be operable using central locking system.

Hope this will help you,
Teddy

Post by **scot850** » 11 Jul 2016, 10:27

Many thanks for the reply.

So 'testing' of the wiring/power to the circuit is not practical. Only way then to test the wires in the trunk lid is to buzz them out I guess.

The key lock in the trunk is in the vertical position. I have tried it in both horizontal and vertical position, tried re-setting the alarm system using the driver's door lock and it does not lock/unlock unless you do it manually ( as a side-bar I discovered I do no have 2 keys but a key and a valet!).

I can hear no activation attempts from the trunk lock. So I will pull the lock and try adding power directly to it to see if it will work at all. This will hopefully point to if the issue is the lock mechanism itself or the wiring.

The lock for the fuel flap does not respond either, so out it will come and a visit to PnP is on in a few days for the 50% off sale!

Neil.

Post by **scot850** » 11 Jul 2016, 14:57

So I removed the whole latch mechanism to check if there is anything broken. There is some question in my mind about the plastic retainer for the rod from the lock mechanism at the end in the latch mechanism. It looks like it may be broken.

If I want to test the motor, which connectors do I use of the live and negative?

I'm guessing I put power to pins 4 (to lock) and 5 (to unlock), while holding the ground to pin 2 as the negative/ground in both cases?

Neil.

Post by **scot850** » 11 Jul 2016, 15:41

Having looked at the mechanical portion for a while, I now have figured out why the electric trunk lock does not work when the mechanical lock on the lid is turned horizontal. When in this position, it moves a spring loaded lever which prevents the lock engaging with the mechanical lock. The electric motor still works but just does not engage with the mechanical portion.

Whew. Now to see if the electric motor works. Any idea how much current is required?

Neil.