December 10th, 2024 Posted in Narrowboat

1.8 BMC narrowboat control panel rewire

The recent battery rewiring on my 1.8 BMC engined narrowboat raised many questions. The alternator wiring didn’t make sense and the leisure alternator wasn’t charging, which led back to a wiring mess in the control panel. Some things needed fixing, some removing and a new fuse/relay box adding to get things working properly.

What was wrong?

Highlights include nothing being fused, live wires being red, brown & black, and the main ignition live (which was also the glow plug feed) being stuffed into a single 10mm crimp.  There were six identical brown wires for various sensors and the alternator warning light feeds. A blue wire wasn’t connected to anything on either end!

The starter alternator output was a black 8AWG cable (8.5mm²) that ran to the control panel ammeter before heading back to the battery. The cable wasn’t thick enough and voltage drop on that run was massive, so wouldn’t be charging the battery very well.

The leisure alternator wasn’t actually connected to anything either – the two ring terminals waving around should have gone to an ammeter then back to the batteries.

The Rewire

All lives are now red, and all earths are black. Some of the brown wires were replaced with orange/green and I want to replace the others with separate colours too. Brown is used on the AC side and shouldn’t be used on the DC side as well (source). The control panel feed is now fused.

Ammeters Removed

Both ammeters are now disconnected as the Victron Smart Shunt can monitor ampage in and out of the leisure battery bank, and voltage of both battery banks now. That’s also reduced the cable runs and number of connections from alternator to the batteries too, so they should charge better.

Ignition Switch

The Lucas 128SA style ignition switch has off/accessory/glow plug/starter positions. The glow plug feed can pull up to 100 amps so needs thicker cable than the original 8AWG used. That was also badly terminated as it didn’t fit in the 9.5mm female spade connector on the switch. As 10mm² definitely wouldn’t fit into that size spade, I decided to upgrade to a relay switched feed for the glow plugs so smaller wires can be used to switch the glow plugs on.

Thicker cables laid as everything was 8AWG at best, which is only around 8.5mm². The glow plugs are now fed with a 16mm² cable from the alternator to the fuse and relay box, then 10mm² cable from there to the plugs. This all lives in a waterproof box under the control panel.

Connections

All connections are crimped and wrapped in heat shrink and any chafed wires replaced. All the twisted together and taped connections for the panel lighting have been replaced with Wagos. The panel earth now terminates in an insulated power post and then feeds the panel, and chocolate blocks replaced with Wagos.

Resources

Diagrams & posts in the ‘12 volt boating group‘ and the articles on TB Training were vital to understanding the engine wiring on a 1.8 BMC narrowboat engine.  Calcutt boats sell PDF manuals for the BMC engines for a few quid and also sent me a wiring diagram, so thanks to the guys there.

I bought and crimped the heavy wiring at the excellent Johnson’s Chandlery, with tools, fuses, connectors and smaller wire from 12vPlanet (fast technical help and very efficient delivery) and Vehicle Wiring Products, with some bits from the marina swindlery.

Summary

What started as fixing my batteries down for the BSS escalated into pretty much a full rewire of the engine bay and control panel. Cutting corners isn’t in my nature so once I’d seen the bodges in the original wiring I had to replace it. Now that’s all straightened out I can fit an inverter/charger and solar next.