JX engine bay earth?

[RogerT]

Hi folks
I'm re-doing the engine bay wiring, as per my post (https://club8090.co.uk/forum/viewtopic.php?f=39&t=154441" onclick="window.open(this.href);return false;) in the electrical thread, but am struggling to find the engine bay earth point - LHS as referred to in the wiring diagram. I need to make an earth for the Coolant pump thermoswwitch (F95 in the wiring diagram) and for the Glow plug engine temp sensor (G27 in wiring diagram). Where do I connect these to? Should there be a pre-existing earth point? Someone did reply with a photo in the above thread, but I didn't know what was in the photo...

Otherwise I'm doing not too bad - wired up the plug for the coolant pump, checked the other wires, but have discovered the connector for the coolant level sensor is wet so I'm guessing the actual sensor pins are leaking.

Posting this in Mechanical as seemingly so few people look in Electrical.

[ZsZ]

Under the air filter, near the wiring loom, there should be a hole with M6 thread. The earth wires should be bolted there.

Here on the left side of the bay:

http://www.vwt3.hu/node/127" onclick="window.open(this.href);return false;

[RogerT]

Thanks, air filter out then I guess...

[Oldiebut goodie]

[RogerT]

Thanks for highlighting that OBG. I peered in from underneath, but nothing to see. I'll just drill and tap a new hole in an accessible location near the electrical box, that seems easier than trying to find the original hole.

Heaven knows, one more hole isn't going to make a difference!

[Oldiebut goodie]

I doubt that you can see it from underneath very easily, it is quite close to the chassis member right in the angle of the body and chassis where it will be covered with underseal and carp.

[syncroandy]

As the engine-bay harness runs along the left side, underneath the airfilter, you'll need to remove it for access to do anything much on the wiring. The earth points have an extra steel plate spotwelded to provide necessary thickness for the screwthread, if having to re-make an earth point (eg. snapped screw) I would recommend placing the hole right next to the existing one so you can tap a decent bit of thread. These earth points really are critical so don't be tempted to skimp, a self-tapper through a ~1mm panel is a bodge IMO.

If you have problems with your JX harness I would suggest simply repairing whatever is faulty (eg. replace corroded terminals) rather than trying to improvise workarounds.

If you having trouble following the earth path on the JX wiring diagram, be aware that several sender earths etc are connected to engine-bay earth via the rear lighting harness, as there's an earth wire between T7a/4 and T7/7 (page 83/4).

TBH, if you have multiple issues to deal with it'll probably allow you to do a better job if you remove the harness completey to work on it on the bench. The GP relay is fixed into the black box so it easiest to take that out along with the harness after unplugging the connectors from the main harness to the front and the rear lighting harness.

[RogerT]

Thanks, I really appreciate you all taking the time to help me on this. Air filter out then, and doubtless wiring box too. I can replace the GP fuse strip too - that's missing as well! And I was kind of ignoring the wires with cracked insulation down near the glow plug bus bar - likely from the heat of the engine. Might as well do the job properly if I'm doing it at all. Hey ho, on we go...

[ZsZ]

Thx Oldie for the highlight. The easiest access is by taking the air filter out.
As Syncroandy said, there is a strenghtening plate welded, and there is another one beside that about 10cm in the direction to the junction box. This second one can be accessed easier when the filter is in. They are present on the petrol body too.
It is worth cleaning the earthpoints (resoldering the connections) anyway.

[syncroandy]

Until pretty recently I used to recommend the option of just buying a complete new engine-harness from VW, as they were only around £150, but they all seem to have gone except for the KY one (no coolant pump) and they's silly money. Seems like they have heard of scene-tax at Classicparts..

[RogerT]

Air filter out, earth for the rear lights nestling underneath, as predicted. I'll clean it up, add earths for the sensors, tackle other knackered wires, replace the coolant level sensor, and all should be good, or at least a step in the right direction

[RogerT]

Hooray, I've succeeded! The coolant pump now works when the sensor connector is shorted. Clearly I've no idea if the sensor works at this stage, but I'll find out at some point I'm sure.

I do however need to investigate the coolant level sensor, the light should flash when it is disconnected, but it doesn't! Not much use like that. The wiring to the junction box in the engine bay is good, so I'll trace it forwards. I guess it is either the electronic module (although I do get the flashing light at startup) or the positive wire to the sensor is shorting somewhere, so the circuit is always complete.

The sensor is also dodgy as the top of it is wet suggesting the body of the sensor leaks. Could the connecting pins being wet be enough to cause the false positive when it is disconnected?

Ideas on a postcard...

Notwithstanding that, I was dead chuffed to remake the earth point (the old one sheared when I tried to undo it) and have a functioning coolant pump. Thanks to this forum again to

[Oldiebut goodie]

I had water coming up via the pins on my sensor - I had found water in the connector also and wondered how it had got there.

[RogerT]

And how did it work while it was wet, Oldie? Did your sensor read full or empty, or - there were plenty of other problems?

[Oldiebut goodie]

I really can't remember, it was a long time ago. There must have been a reason as to why I was looking at it though!