124 Estate Blowing Fuse C Central Locking

[230K]

Hi

Spent most of the day trying to solve a fuse blowing problem on a 1993
300TD.

It is fuse C that operates the central locking and soft closure on tailgate etc.

During the day i have isolated vacuum pump, tailgate closure system, and all of the twelve wires that go into the tailgate through the flexi beside the hinge. Still it wants to blow a 16A fuse. I short it out for a short while and the central locking and soft closure works fine. I have checked the roof lights are not earthing etc etc. It doesnt seem to be a dead short although i have no way of measuring above 20A.

Has anyone any tips or pointers of what to look for.

Thanks,

230K

 

[television]

By disconnecting the motor only you could measure the residual current.

There is a good chance that it is the closing motor, the problem being that it does have to run very long, so any overheating would not show up.

If the motor can be removed easily then it can be run and a current check done

 

[grober]

Sounds as if you have a short to earth somewhere. I would have put money on it being in tailgate area but you seem to have checked that?? Other possibility is a similar short in the cabling at the door hinges of the normal doors. worth checking out ---do it in the order of the most used >i.e. drivers front first etc

 

[230K]

Thanks

Was gonna check the doors but just didnt have the heart for it and the daylight ran out too. Fiddled around with the pipe/trunking that takes the wires to the doors but i will check the 2 front doors. Is it power or vacuum that goes to the key switch/handle in the two front doors?

230K

 

[bolide]

Do you mean that it blows fuses with all the tailgate wires and the central locking pump disconnected? If so it can't be too hard to find - there can't be much left

If it blows only with the pump connected I suspect the pump is bad

There must be a pretty significant current draw somewhere to pop a 16A fuse. If it's not a bad motor then I'd expect the wiring somewhere will be good & melted

Nick Froome
www.w124.co.uk

 

[television]

Thanks

Was gonna check the doors but just didnt have the heart for it and the daylight ran out too. Fiddled around with the pipe/trunking that takes the wires to the doors but i will check the 2 front doors. Is it power or vacuum that goes to the key switch/handle in the two front doors?

230K

You have both power and vacuum going to the doors,contacts on the key switch that turn on the vacuum pump

 

[grober]

As far as I know there's power- 3 wires- and a vacuum/pressure pipe to the 2 front doors and boot and just vacuum/pressure pipe to the rear doors and petrol filler cap. so just the front doors to check.

 

[television]

Soft closure uses an electric motor in the back door

this is the rear door locks

http://www.detali.ru/cat/oem_mb2.as...GM=717.433&CT=F&cat=15U&SID=74&SGR=030&SGN=02

 

[230K]

Do you mean that it blows fuses with all the tailgate wires and the central locking pump disconnected? If so it can't be too hard to find - there can't be much left
www.w124.co.uk

Yes it blows the fuse with pump disconnected and the harness to tailgate on both sides disconnected just beside the tailgate struts you know under the roof cloth.

Might check the 2 front doors

Thanks,

230K

 

[Dieselman]

As grober said, perform a continuity check from the fuse holder to ground as this mucst be a significant load to draw more than 16A.

 

[230K]

As grober said, perform a continuity check from the fuse holder to ground as this mucst be a significant load to draw more than 16A.

The draw is approx 20A my meter only goes to 20A when above it just reads 1. With the ign on (glow plugs) it would drop to 18.5A or so (obviously cos the battery is strained with heaters) so pulling just around 20A.

I will get to the bottom of this. Will check continuity to earth from fuse terminal to see what it is but it should be around 0.6 ohm if its drawing about 20A?????

Update i checked resistance to ground about 0.5 or 0.6 ohms.

230K

 

[230K]

Hi

Update:

Central locking is now working again. It seems the switch in the door lock on the drivers side had shorted out and melted the wires going to the door in the process. Traced all the wires to the door and remainder of the melted ones replaced and taped up and have all up and running again without a harness to the drivers door. New central locking loom is £98 and new lock is £128 so i will maybe make do with the beeper on the alarm. Key lock was never used anyhow.

Thanks for all your help, i am a lot wiser with regard to the Central locking system now.

230K