Battery drain - cause?

[RawbDidIt]

A little bit of progress today. Battery voltage on the posts is 12.5V - no lower than yesterday so when disconnected the battery seems to be holding up.

Traced the drain to the lead that runs over the fan shroud to the Fuse Relay Centre. Took its lid off and pulled all the relays and fuses but the drain persists.
Is there anything coming out of that box unfused? If not - an internal fault? If so - what? Where do I look next?

Just because they were there and I could, I pulled the top two plugs on the engine ECU - no difference. Ditto a big grey relay thing beside the FRC.

Is it likely that there is an internal fault in the FRC? Are they known for this?
TIA.

It's possible the fuse box itself is creating a draw, but it's more likely that there's something aftermarket on the back of the box that's causing it. On the rear of the box there's 2 bolts for auxiliary loads, typically it's used to power trailer brakes or aftermarket amps. Check to see if there's any wires connected, if so, disconnect and retest. They're not fused, so it would explain why removing fuses and relays isn't revealing the issue.

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[Pinger]

It's possible the fuse box itself is creating a draw, but it's more likely that there's something aftermarket on the back of the box that's causing it. On the rear of the box there's 2 bolts for auxiliary loads, typically it's used to power trailer brakes or aftermarket amps. Check to see if there's any wires connected, if so, disconnect and retest. They're not fused, so it would explain why removing fuses and relays isn't revealing the issue.

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Cheers for that - you've probably nailed it.
Nothing mounted on the two (vertical) studs at the rear of the box - only the incoming on the horizontal stud. Must be an internal fault then. Time to open it up.....

Posted some photos for you of the fused junction box. They appear on page #3 in case you missed them. First pic is as its mounted on the fan shroud, the rest removed for better access.

 

[RawbDidIt]

Cheers for that - you've probably nailed it.
Nothing mounted on the two (vertical) studs at the rear of the box - only the incoming on the horizontal stud. Must be an internal fault then. Time to open it up.....

Posted some photos for you of the fused junction box. They appear on page #3 in case you missed them. First pic is as its mounted on the fan shroud, the rest removed for better access.

Saw that, thanks for the pic, I'll see if I can find one new, that's a great place to put my light fuses when I install them.

So you have disconnected all loads, and the drain is still there, but goes away when the main power to the fuse box is disconnected? That's just odd. I'd double check before going through that replacement.

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[Pinger]

Saw that, thanks for the pic, I'll see if I can find one new, that's a great place to put my light fuses when I install them.

It sits so neatly on the shroud that only the lack of a GM part # stopped me thinking it was an original fitment.

So you have disconnected all loads, and the drain is still there, but goes away when the main power to the fuse box is disconnected? That's just odd. I'd double check before going through that replacement.

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Tried it all ways round. Any time that lead was disconnected - no drain. With it connected and nothing else - immediate 1/4 Amp draw.

Loosely my plan is to remove it and start probing. Maybe it has distorted a bit and causing a short, maybe there are electronics in there that have failed. I'll have a look at Haynes for a clue as to what to expect first. Thing I'm not getting is why there'd be an earth (or earth path) inside it but I guess the relays need a ground. Weather permitting, I'll know more by this time tomorrow.
As for replacement - only if the UK supplier I use is open.... (UK in lockdown).

 

[RawbDidIt]

It sits so neatly on the shroud that only the lack of a GM part # stopped me thinking it was an original fitment.



Tried it all ways round. Any time that lead was disconnected - no drain. With it connected and nothing else - immediate 1/4 Amp draw.

Loosely my plan is to remove it and start probing. Maybe it has distorted a bit and causing a short, maybe there are electronics in there that have failed. I'll have a look at Haynes for a clue as to what to expect first. Thing I'm not getting is why there'd be an earth (or earth path) inside it but I guess the relays need a ground. Weather permitting, I'll know more by this time tomorrow.
As for replacement - only if the UK supplier I use is open.... (UK in lockdown).

Yeah, the relays will have a ground path, may be some slightly conductive stuff got in through the years and created a ground path on the backside. May even be able to pull it and give it a thorough cleaning, but if the part is cheap, it might be faster to replace outright. I've never heard of the fuse box itself having a parasitic drain, but hey, if it can happen, at some point it will.

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[HotWheelsBurban]

That's an interesting piece of hardware, don't think it's factory. Neither of my trucks had a box like that. Could be something that the company that fitted the LPG system to it added. I haven't seen one of these trucks with the LPG setup so l don't know what it is supposed to look like. My trucks have 2 positive cables; one goes across the fan shroud and down the left side to the main junction box for the computer. The other one goes down to the starter solenoid. Our trucks are prone to corrosion in these cables, and it's not always obvious. Good luck!

 

[PlayingWithTBI]

Yeah, the relays will have a ground path

We had an issue with Triac relays bleeding voltage through them lighting up a pilot light on the hydraulic valves, had to put resistors on them to drain the Triacs. This was on a PLC controlled (Allen Bradley) extrusion press, not automotive though - just a thought. Maybe pull 1 relay at a time?

 

[Pinger]

That's an interesting piece of hardware, don't think it's factory. Neither of my trucks had a box like that. Could be something that the company that fitted the LPG system to it added. I haven't seen one of these trucks with the LPG setup so l don't know what it is supposed to look like. My trucks have 2 positive cables; one goes across the fan shroud and down the left side to the main junction box for the computer. The other one goes down to the starter solenoid. Our trucks are prone to corrosion in these cables, and it's not always obvious. Good luck!

I suspect it is something to do with the LPG system but not obvious what as nothing is taken from it for LPG.
From the battery (mounted passenger side) I have two leads. One to the starter and the other to the junction box. From there, two leads, one to the alternator and the other to the FRC. What it appears to do is place a fuse between the battery and the alternator and FRC - which you maybe don't have.

 

[Pinger]

We had an issue with Triac relays bleeding voltage through them lighting up a pilot light on the hydraulic valves, had to put resistors on them to drain the Triacs. This was on a PLC controlled (Allen Bradley) extrusion press, not automotive though - just a thought. Maybe pull 1 relay at a time?

I pulled the relays along with the fuses - no joy.
I'm hoping I can get into it (tomorrow) and find something obvious along the lines of suggested in post#35. More tomorrow....

 

[Pinger]

Some work done today but no progress!
Opened up the FRC. Nothing obviously wrong with it. Someone has slaved from a relay earth tag and joined in 4 brown wires that then disappear into the loom. A bit further down the loom 4 black wires emerge and are connected to an eyelet that bolts to the body as an earth. Suspect this is all LPG stuff. Opened up the trunking on a huge chunk of harness and there's taped connectors all over the place. Next step is to check the colours of wires the LPG ECU connects with and try and identify what is what. Am I correct in thinking GM use black cabling for earths? Does anyone recognise the description of the 4 black wires earthed to the body as something they have on their truck? It bolts to the inner wing horizontally (bolt head pointing upward and slightly inclined towards the centre) and the bolt's head is 13mm across the flats. There's a shitload of wires coming out of the FRC - but they are all supposed to be fused?