MD2030-D electrical harness

[Lyra]

Yesterday when  when I activated the heaters before turning on the engine, the electrical wires harness began to burn - seems a result of wires corrosion over the year. Apart from the heaters wire some other wires seem to have been damaged and in any case it might be a good idea to replace all.
The harness is listed in marinepartseurope.com at more than 300EU.
Anybody knows of another source for this harness, before I go ahead an make one myself - it is the harness from the relay box to the engine (the one going to the instrument panel did not get damaged).
It does not seem to be a great problem to make one but if I do I will probably use a single wire color (tinned - this time) and have to mark somehow each wire - probably heat shrink sleeves.

[Salty]

If you go down the DIY line, I’d recommend giving this firm a look at for cabling and other parts for making a harness. They carry a very large stock of cables of differing colours and with tinned copper wire as a speciality. https://kojaycat.co.uk/

[Lyra]

Thanks for the pointer to this site (may also help me with something I need for work)

Just noticed in the diagram that most of the cable are red or black based, both of which I already have in 1.5 and 2.5 mm2, so it would be a simple thing of just adding a color band at the ends (ordered from ebay a set of various colors heat shrink tubes). Maybe the only thing I will need are new sockets for the relays.

[Lyra]

Just an update - harness fixed (and engine running again)

The 2.5 mm wires (high current)  were changed to new tinned wires.
there were two 1mm wires which had their insulation melt over short length exposing the conductor (not due to them getting hot but due to adjacent wires that burnt), but since they are attached to the Amphenol round connector and I could not source new pins for that, I just cut the damaged length, replaced with 1.3mm tinned wires, soldered and heat shrinked the solder point.
two additional wires had the insulation melt very slightly so I just covered them with an additional layer of insulation tape.
One of the relay holders got really damaged from the heat - this I was able to get from the local Volvo dealer (although it is basically obsolete) together with the required crimp terminals.
The heaters relay contacts got fused - replaced with a new relay. At the moment I do not know what lead to what - was it the contacts that did not open and caused a non stop high current that lead to the wires burning or was it the heat generated by the wires due to corrosion that led to contacts fusing. One thing is almost sure according to what was left form the high current wires - they were badly corroded.

[Salty]

Hi Lyra,

Did you take any photos of the area of damage before you made up your new harness?

My B36 is a couple of years older than yours, so I’m a bit worried in case of having a similar problem, so a heads up on where the burning took place in relation to the engine would be great, thanks.

[Lyra]

Did not take photos, and basically most of the length of the wires is inside plastic shrouds so it would be really hard to know what goes inside. In my case it was the heating element wire that totally burnt, partially melting the shrouds and the wires nearby.
The potential for a problem is with the red 2.5 mm^2 wires which feed the starter relay and the heating elements due to the high current which they carry. All other 1 mm^2 wires are signal wires with very low current.
I guess what you could do when time allows is replace only the two thick wires - both go to the relay bases so replacing them is possible as only flat female terminals are required (and a ring terminal at the end of the heating wire). Use the old wire to pull the new wire into the shrouds.
Note that the only way to do this work is remove the whole harness and relay box and do it on a table - but the electric schematic in the manual is ok so knowing which wires goes where is not problem. some wires also have unique endings or go to totally different places so it is hard to switch between wires, except for 2 wires on the alternator

[Salty]

Many thanks for the tip Lyra.

I’ve got the MD2020 engine on my 36, but I’ll be taking a very close look at that wiring harness over the next couple of weekends.