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MG MGB Technical - Route for main loom

72-roadster, rhd
Can anyone supply me with a picture of the route taken by the main loom under the dash. I thought all was going well but I seem to need to take it further left for some switches, but further right for the fuel guage, so obviously I've done something wrong in the bends and twists.
Richard Coombs

I was under the impression it went straight across from right to left, with tails coming out at appropriate points for each component. I think there are two possible right-to-left routes though - one behind some bracing struts, and one through them which will bring the main run closer to the dash.
PaulH Solihull

It certainly goes from right to left. I've laid it at the top, against the bulkhead, and then brought it sharply towards the dash to avoid the central dash air vent tubes. These appear to limit the 'left' movement so that the tails that go to the fan switch seem a bit shorter than is comfortable. The whole thing then travels to the right to get the reamining tails towards the RH dials and switches, and the ignition switch/indicator stalk of course. My route seemed so convoluted I thought there must be a better way.
Richard Coombs

Are you sure you don't have a LHD harness? It makes no sense for the harness to come from the extreme right-hand side to the middle for those controls, then back to the right again for the column. My 75 V8 has the tails for the column controls coming out as it passes over the column, which makes much more sense. Also having had a look (instead of relying on memory) it passes behind the wiper motor then comes forwards to pass the braces on the dashboard side, not go through them. I remember now that was the choice - not behind them i.e. close up to the firewall or through the middle. I did try through the middle on my 73 roadster but the tails were too short, so had to pull it back out of the braces and run it past them on the dashboard side instead of through them. It also means you can pull the dashboard forward with everything connected, also connect everything before fitting the dashboard.
PaulH Solihull

Paul, what an interesting theory, and maybe it is, though I've not had to think about it before. It would certainly answer why there appears to be such a large amount of loom. You may be able to see what I'm talking about in the picture. I've run the loom from the extreme rhs, behind the wiper motor and wiper drive until it reaches the first fresh air vent. Up to this point, other than the wiper motor connections, there are no tails - in fact the first one is a group of wires intended for the fan, wiper and lights switches, so left of centre to about centre.
The tails for the instrument lighting, speedo, tacho, regulator, ignition, indicators and fuel guage all appear about a foot later and, as you can see this means the loom is twisted back on itself like a gooses neck. All of which seems to point to a lhd loom, but why would this be?
The Heritage certificate shows the car was definitely a rhd at manufacture but I have no documentation in the period from then to 1992. A lot can happen in 20 years but export to the US, with conversion to lhd, and then return and reconversion seems highly unlikely. Maybe the car had a loom burn out and the PO/garage used what they had?
In any event, apart from the excessive cabling, all the right connections are there but not necessarily in the right order (thanks Eric M!!).
Thanks for the idea Paul. Any other thought would be gratefully received.


Richard Coombs

Richard

You have it correct as all looms were made for the USA so they just looped them back for UK cars.
It did change later to country specific looms
Ste Brown

Thank you! I was awake all night with a 'should I/shouldn't I'dream about cutting my 'lhd' loom to make it a 'rhd' loom, if only to make it fit more easily. I rather like Paul's note about being able to fit the dash with the controls already connected to the loom so I may do some surgery anyway.
Richard Coombs

Another interesting theory, and indeed from the Parts Catalogue it appears that the harnesses were common until the Mk2 in late 67 when the North American spec cars started diverging in more ways than which side the steering wheel was located. After that the harnesses were separate as North America (and eventually Germany and Sweden) got more and different electrical circuits. There was a new harness for the UK Mk2, and it changed again for the 69, 70, 71 and 72 model years so I would have thought it would have lost the extra length by 1972 as they had been making UK/RHD-specific harnesses for five years by then. It could have been rewired and an earlier harness used, but then there would have been some incompatibility between wires and components. But maybe *non*-USA LHD cars used the same wiring as RHD, so they were still looped back. All LHD cars didn't standardise on the North American spec until 77. Whilst the V8 was never marketed in LHD form several were built for Federal testing, going by mine they either had a special harness or 'extenders'. Maybe my 73 also has the looped back harness, I'll have to look next time the car is handy. Certainly by 1980 they weren't.


PaulH Solihull

A lot of the parts book numbers are to do with the changes to the car in them years ,like alternator/dynamo,toggle switches/rocker swithes,change in wiper motor style so differences were needed in those years.
Both my 70GT and 63Roadster had the long loom.
Proberbly cost cutting made the looms shorter.
Ste Brown

Richard,check on the "MG Experience" website,there are some good pic of how the harness routes.I will be installing one in my 1972 B. Rich O
rich osterhout

This thread was discussed between 15/11/2010 and 22/11/2010

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