thepurpleblob

I've got two good batteries and I've been trying not to let either of them go completely flat. I checked for a hot relay a couple of days ago and found nothing conclusive.

I'm happy enough to try again.

SwayBar

Have you tried puling relays one-by-one to see if the drain stops/reduces?

Let's say that works, then you know which system to diagnose based upon the relay.

thepurpleblob

I've made a bit of progress - but I don't want to tempt fate as more testing is needed.

The current theory is that it's the X-Bus relay sticking on after the car is used. If this is true, it's clearly dropping back out when I disconnect the battery (to insert the ammeter) which is why I don't see the problem. I don't own a clamp meter.

Anyway, I'm recharging the battery and have replaced the relay in the hope that it's as simple as that. I'll give the car another run and see what happens.

Hey_Allen

Have you tried checking the system drain without disconnecting fully?

If you use clips to connect your meter to the battery terminal and the post of the battery, you can carefully lift the lug off if the battery post without de energizing the wiring. You want the meter to be in parallel to the connection, and the major current draws offline before you do so, or the circuit protection fuse in the meter will blow.


(edited to correct typos from mobile keyboard.)

Mrmerlin

I had that X bus relay stick on my 88 I found it by touching it with my finger after i had recharged the battery, yes it was warm

thepurpleblob

I'm just rambling now.... it definitely looks to be the X-Bus relay that is staying on. However, replacing the relay (with a new one) didn't fix it. I also took apart the old one and it all looked fine. As it consistently drops out (and stays out) when the battery is disconnected, it would not point to a "sticky" relay anyway.

So, it would appear to be something else energising the relay. That's as far as I've got. I now need to have a good look at the wiring diagram and a poke around to see if I can establish what's keeping it energised. It feels like progress....

Mrmerlin

Try removing the rear window defrost relay mext

FredR

Even if the x-bus relay is sticking on the current still has to go somewhere given an energised bus in and of itself does not consume current

Alan

You don't need a clamp meter to do this - connect the meter across the battery negative post and the ground point - then disconnect the ground strap. To verify if its the X-Bus staying on simply remove the relay overnight, this a better test than replacing the relay (since it could be an issue with the coil control not the relay - eg ignition switch)

Alan

Alan

I would also wind the windows and sunroof to the 1/2 way positions and try again - keeping the meter connected at all times and removing the ground strap to test.

Alan

thepurpleblob

Thanks - I've got a bunch more things to check to confirm if the X Relay is the issue (or part of the issue) and, if so, why it's causing such a huge drain. Hopefully, I'll not be back later saying "it wasn't that"

thepurpleblob

And... it's looking like the rear window heater relay/timer. I'm not calling it yet because I've been wrong before but this seems to be *a* proble if not *the* problem. When the ignition is switched on it comes on (regardless of the switch position) and it stays on when the ignition is off. Somebody did mention checking that...

Just for the record... it doesn't stay on with anything less than the proper battery connections. Clearly, there's too much resistance in a test lamp of meter to keep it pulled in... even with some acrobatics keeping them connected while the battery earth is removed.

Realistically, I'll need to give it a few days to be sure.

gazfish

Crack an egg on the hatch glass, might as well make use of it 😀
Hopefully you’ve nailed it.

thepurpleblob

It never occurred to me that the defroster would actually work. Nothing much else has

But, yeh, I'm calling this "fixed" (or at least diagnosed)