Multiplus 1 - 12/3000-120 no lights

Right, this one's close to home — had almost the exact same head-scratcher on the narrowboat last winter.

Older Multiplus 1 sitting in a cramped bilge area, barely enough room to get your hand behind it let alone read any indicator lights. Mine went completely dark — no LEDs whatsoever — after I'd been doing some work on the starter battery circuit. Turns out the unit had gone into some kind of protection mode and the interface was effectively dead to the world.

Few things worth checking in rough order:

• Fuse on the DC input side — sounds obvious but the main ANL fuse or the smaller blade fuse near the terminal block can blow without any drama. Easy to miss in poor light
• Low voltage lockout — if the leisure or starter bank dipped below a threshold whilst the unit was under load, Victron's protection kicks in hard. Try a known-good 12V source directly to the unit if you can manage it physically
• VE.Direct or MK3 connection — if you can get a laptop down there with VictronConnect, even briefly, the diagnostic info is invaluable. Saves hours of poking about
• Check the temperature sensor wiring if fitted — loose connections there have caused odd behaviour on mine before

The boat environment is brutal for electronics honestly. Condensation, vibration, salt if you're coastal... I've started putting a small desiccant pack near the Multiplus which probably does very little but makes me feel better about it 😄

What's the state of the battery bank itself? If the starter battery has been draining, worth checking whether anything back-fed oddly through the system.

What have you already ruled out?

@Boycie had a similar one on my static. Before assuming the worst, worth checking the internal fuse on the DC input board — they do fail silently on the older Multiplus 1 units, especially if it's ever seen a high-current spike.

Also, cramped bilge = potential condensation issues. The main processor board has a known weak point where corrosion on the ribbon connectors kills all LED output simultaneously, which can look like total failure but isn't.

A few questions that'd help diagnose:

• Any voltage actually reaching the DC terminals when you measure it?
• Does it make any sound when DC is applied (fan tick, relay click)?
• Has it ever thrown a fault previously, or is this first failure?

The relay click on power-up is often the quickest way to tell if it's a board issue versus something upstream.

@BlownFuse good shout on the fuse — though also worth pulling the board out and checking for corrosion on the connector pins themselves. Had my Multiplus in the shepherds hut go completely dark last autumn, zero lights, nothing. Turned out one of the DC input connectors had corroded badly enough to break continuity entirely. Looked fine from the outside.

Bilge environment especially is brutal for that — moisture gets everywhere.

Also — silly one but — has anyone confirmed the rotary switch on the front isn't halfway between positions? Mine did exactly this once, sat between "charger only" and "on" and just... went dark. No fault, no lights, nothing dramatic.

@Boycie this rings a bell from my shepherd's hut setup — though less cramped than a narrowboat bilge, I imagine.

One thing not mentioned yet: have you checked the remote on/off terminals? On mine the connection had worked loose and the unit just sat there completely dead — no lights whatsoever. Easy to overlook because it looks like a total failure but it's a two-second fix.

Also worth confirming you've got voltage actually reaching the DC terminals with a multimeter rather than assuming the batteries are delivering. Had a corroded Anderson connector on my narrowboat cable run that was showing 12v at the battery but dropping to almost nothing under any load.

What's your battery setup? Lithium or AGM can behave quite differently when the Multiplus decides something's wrong and goes into protection.

Had this exact grief on my motorhome Multiplus last year — spent two days convinced it was the control board before finding the culprit.

Check the temperature sensor ribbon cable. In cramped installations they get kinked or partially unseated, and the unit just sits there doing absolutely nothing — no fault lights, no startup, nothing. Looks completely dead.

Pull the board carefully, reseat that ribbon connector firmly. Victron's own service manual covers it but it's buried about halfway through.

@TrevorHughes is right to flag it — no lights at all is actually a narrower diagnostic than people realise. A partial fault usually gives you something on the LEDs. Total darkness points toward either your fuse (already covered) or something interrupting the startup sequence before it even gets going.

Worth ruling out before you start throwing money at control boards.

@ExmoorCamper that two-day diagnostic rabbit hole is painfully familiar — I lost a whole weekend on my garden office Multiplus convinced I had a dead control board, turned out to be a dodgy earth connection on the DC side causing all sorts of phantom behaviour.

Worth checking: with these older units, the bulk capacitors can fail silently — no bulge, no smell, just nothing. A multimeter on the DC input terminals while someone else hits the switch can tell you a lot. If you're seeing voltage drop the moment you energise it, that's your culprit rather than the board itself.

The bilge environment is brutal on electrolytic caps specifically — moisture and temperature swings are basically a perfect storm for early failure.