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MG MGA - Wiring loom

Hi guys, haven't been on for a while, firstly a big thanks for all your help this year, being new to my MGA which I love ! You have all been a great help in me sorting out some problems,
I had a bit of trouble with wiring last week and found the original 1956 wiring pretty poor condition, so I think before the five speed conversion starts, more important is a new loom.
I'm assuming some of you have fitted a new loom at some time, so questions are:
Is it straight forward ?
Can I do it a bit at a time or do I have to take the whole lot out First ?
And are there any tips you can give me to stop me screaming B***** while I'm working on it, Haha!
Cheers Jack.
Jack New Forest

Jack, from my experience I would advise stripping it out and taking it to a wiring expert for refurbishment. Could save you a lot of money as a new loom could be expensive. Tackle it as a whole - bit by bit could be messy.

I have found there is usually not much wrong with the old loom and it can be reworked.

Tag all the 'ends' before you start, to save confusion at reassembly.
Barry Gannon

My secrets to a fast and easy wiring loom exchange

1. Sit down at a well lit table with a wiring diagram and the loom. Using a test meter, identify each cable and mark it with a flag of masking tape saying what it is. This makes life much easier when attaching the various cables in the car. I still do this although I can pretty much label a loom without the diagram these days. I have just labelled up the 1600 wiring loom like this in 30 minutes, which will be time easily saved when installing.

2. Cut off and keep all the dash bulb holders from the old loom, complete with their cable stub. Then using a soldering iron, remove the small brass ferrule from the end of each cable stub. Then remove all the new bulb holders from the new loom (again using the soldering iron and then you have a few ferrules over to cover the lost ones)- on the 1600 loom I will have to cut these off, as they are crimped not soldered..... The old holders are good and hold the bulbs nice and tight, the new ones are in my experience cr*p. This is confirmed by the new 1600 loom.

3. Cut the old loom apart to make removal easier. I try and rescue the longer lengths of original wire with the colours for front sidelights and indicators, and for bridging between the horns. This is because these wires are never in any kit, even if it claims to be a full harness. This again is the case with the newest loom on the bench, which has cables as far as the inner wings and no further.

4. Buy the correct tool for the connectors. It makes life MUCH easier, and causes less potential for injuries than when the alternative small screwdriver slips and spears a hole in your palm. See the image attached

5. Buy extra connectors - every MGA loom I have ever installed has always been short on connectors, some have none at all!

6. The baffling left over wires at the dash which have no connectors go to the horn button, which has to be unmounted to get at the screw terminals!

7. For the lighting switch, there are too many red wires to be able to get them all easily into the same terminal at the light switch. But one of them goes to the F switch, so you can make life easier by moving one of the the cables to the same terminal at the F switch, and that saves a lot of fiddling

8. The red wire to the map light switch is often missing, it is just a bridge wire from red terminal of F or L switch to the map switch.

9. Be prepared to find other electrical components are beyond saving as you disconnect them. They are usually indicated by bodges around them.

10. I always modify to -ve earth and add an under dash 12V socket. With modern phones, GPS etc, it makes life much easier for the owner.

11. I always add a fuse for the lighting circuits behind the dash.

12. Avoid Lucar push on terminals wherever possible, use a good crimp tool and add a ring connector for a good connection (e.g. at the coil). The flat metal things are NOT a good crimp tool. I prefer to crimp and then solder. Don't use the crimp connections with a coloured plastic collar - if that is all I can get, I cut the collar away before crimping for a much better job.

13. Use heat shrink tubing to add resilience to any modifications or additions to the loom. This also looks much better than a raw crimp.
Dominic Clancy

here's the connector tool

I never refurb the old looms. This is mostly because the insulation is normally brittle, and the ends of the wires show signs of corrosion (= resistance = lower current / heat / dim lights etc.)

I also now always install LED rear bulbs and in a 1500 switchback white / orange led bulbs to make the front indicators flash amber but sidelights show white.


Dominic Clancy

Jack

100% with Dominic. However, it's always worth looking at MGAGuru. ET-091 to 100 just about covers it.

Make sure you save the sleeves which connect the number plate lamp wires to its terminals. These are not the regular bullets.

Cheers

Dave
Bolney Coupe

I have recently replaced the loom on my Frog and totally agree with the points that Dominic makes.

I am colour blind (good start) and spent ages identifying and labeling each wire in the loom before I started. That stood e in good stead because it isn't always obvious how the loom relates to the terminations. Spent ages with the wiring diagram.

I added extra fuses and relays (mainly to the lighting circuit) and also hazard flashers.

I wouldn't go for a 12v socket but use something which actually was suggested by Dominic previously. On ebay you can buy flying leads with usb terminations. These can be tucked away behind the dash and pulled out when needed. And are actually more convenient that a socket.

And before you start, as Dominic says, make sure you have the correct crimpers/soldering gear to make connections, and you can get good results. Crimping I found needed the practice.

One more thing about fuses: make sure you understand the difference between modern and "lucas" fuse ratings.
Graeme Williams

... oh, and buy Rick Astley's "Classic British Car Electrical Systems"
Graeme Williams

Is that his new album?
Dave O'Neill 2

It is, but only the battery is flat!
Graeme Williams

Graham is more up to date than the text I copy-pasted below. Instead of the flakey connections of a cigar-lights socket I now use USB 12V converters like the one here

http://www.ebay.co.uk/itm/DC-DC-Converter-Module-12V-To-5V-3A-15W-Duable-Dual-2-USB-Output-Power-Adapter-/191217583116?hash=item2c8574c40c:g:-HwAAOSwo8hToBBL

I also buy heat shrink on eBay, as a metre length is much cheaper than getting it at the local places

http://www.ebay.co.uk/itm/1-50-Weatherproof-Heat-Shrink-Heatshrink-Tubing-Sleeving-Wrap-Wire-Cable-/181286737163?var=&hash=item2a3588150b:m:mx3AqsFsBoHagaj_UN7fzng

This is the type of crimp tool to buy - the flat metal ones are a complete waste of money

http://www.ebay.co.uk/itm/9-Ratchet-Crimper-Plier-Cable-Wire-Electrical-Crimp-Terminals-Crimping-Tool-Kit-/172044549807?hash=item280ea77eaf:g:EVkAAOSwZ1lWgiTC

I always buy crimp connectors without coloured sleeves, which I find give a much more secure result - always remember to put a piece of heat shrink on the wire before crimping

A heat gun is the best tool for heat shrinking, although I keep one of these in the mobile toolkit for emergency repairs, and they work well if I can't be bothered to get the flex out for the heat gun

http://www.ebay.co.uk/itm/Gas-Cooker-BBQ-Camping-Lighter-Refillable-Safety-Flame-Lock-Barbeque-Oven-Candle-/182270026838?hash=item2a7023e456:g:Z2EAAOSw8oFXzoIJ

Dominic Clancy

Those ratchet crimpers look good value!
Graeme Williams

I agree with others' comments about Dominic's advice. I installed a complete new harness following his comments, using an enlarged copy of the factory schematic, and Barney's web page that shows all dash harness connections to the gauges. That was invaluable. While intimidated at first, it went well, and I feel its done right. BTW, I installed a new harness from SF, which Barney had a look at before I started, and it was of very good quality.

George
George G.

Dave,

Thanks for your comment "Make sure you save the sleeves which connect the number plate lamp wires to its terminals. These are not the regular bullets." Do you have any pictures of these sleeves or a reference to a supplier? I was not aware that they were different.

Thanks,
Mark
M Wellard

It's not difficult. You just need to be logical about it.
Autosparks in the UK supply looms for a lot of cars; their looms are probably the ones sold by Moss. The loom is 187 pounds from AS; see https://www.autosparks.co.uk/finder. It may be cheaper from Moss.
Photograph all along the loom so you can see where it runs.
Cut the loom out. Whenever you have a switch or other electrical component CUT the wire leaving a 1" tail. Then you'll know what colour wire needs to go back there. British car wire colours from the 1960's are pretty much standard. Search the net; you'll find a list. The diagram in the MGA manual is colour coded too.
Work out where the rubber grommets need to be on the loom and put them on BEFORE you put the loom in the car.
Use an ohmmeter to check continuity. Make sure you remove the battery and the fuses before you start.
You can buy a cheap tool to make fitting bullet connectors together easier.
It's fun.
A Bowie

You need to consider how you are going to tackle the recomissioning. It would be overconfident to just connect up the power!
I made up a lead with a fuse and connected different circuits in turn, replacing the fuse with a rating suitable for the circuits being connected. I used this lead in the connection from the battery to the test circuitry.
Prior to that I used a buzzer with crocodile clips to test continuity. A decent electrical test meter was also useful to check current too, although I personally found the buzzer device more convenient than the test meter for continuity.
Finally, have a fire extinguisher handy!
Graeme Williams

A Bowie: I used an Autosparks loom on the Frog. Quality was good and it looked authentic. The only criticism was some of the bullet ends weren't crimped well enough and if I had to separate the joint again the bullet was left in the sleeve!

The issue to watch with leaving tail ends is whether the colours are correct in the first place. Easy to double check with the wiring diagram just incase a bit of amateur wiring has been done previously. The Frog had totally incorrect colours throughout because someone along the line had made up their own loom using only three colours!
Graeme Williams

A few last things

The new looms NEVER have the headlamp pigtails, so these need to be ordered separately.
http://www.autoelectricsupplies.co.uk/product/439/category/80

The headlamps should be updated from sealed beams to H4 - use three-adjuster buckets and you can go to LED headlamps for a much brighter light and lower current draw. Otherwise keep the existing buckets and use a good H halogen bulb.

Buckets (metal for heat transfer qualities)
http://www.autoelectricsupplies.co.uk/product/995/category/80

H4 reflectors
http://www.autoelectricsupplies.co.uk/product_list/187

LED headlamps
http://www.ebay.co.uk/itm/1Set-H4-Hi-Lo-LED-headlight-Bulb-8000lm-50W-with-Philips-Chip-Truck-Car-Headlamp-/251629959277?hash=item3a9650786d:g:ZOAAAOSwGtRXxPfH

The special sleeves that are mentioned for the license plate light are also required for the original rear lights and front 1500 sidelights: you need 12 of these for a 1500. You strip the end of the wire, push through the hole in the sleeve and bend over before seating the sleeve in the connector on the light fitting. Only use these here to ensure a secure connection and no shorts / fires.
http://www.autoelectricsupplies.co.uk/product/709/category/6



Dominic Clancy

Mark,
I'm pretty sure these are the sleeves which connect the number plate lamp wires to its terminals that Dave is referring to. I sent you an email with more pictures.

Jim


JL Cheatham

Jim

You are correct. They are 0.184 diameter and 0.403 long with a flange 0.25 diameter to stop them falling thru the rather sloppy sockets on the lamp base. Material is plated or tinned brass 0.017 thick.

In fact they are the same diameter as regular bullets but as I recall the wire's sheath goes inside the sleeve with the individual conductor strands folded back over the outside of the sleeve to contact with the socket.

Cheers

Dave
Bolney Coupe

Thanks Jim & Dave,
I thought Dave was referring to a plastic connector so the confusion was mine.

Cheers,
Mark
M Wellard

Jack,

As a footnote, I had no experience whatsoever of auto wiring, took Dominic's advice about three months ago and bought a new loom.

When it arrived and I unfolded it onto the dining room floor I was shell shocked.

A week later it was in and WORKING.

It is sooooo straightforward if you just take everything one step at a time, apply logic and follow the advice given.

Now I would tackle pretty much anything electrical which is a real confidence booster and a great skill to have in your locker.

Good luck !

Aleks
A Stojanovic

"Shell Shocked" - quite agree! A new loom at first sight seems totally incomprehensible. Can't see which end is which and how it all joins together. It is very satisfying as you work your way through it though.
Graeme Williams

Here's a link to an MGA 1500 wiring diagram. I had a poster-size color copy printed at OfficeMax. It's very helpful and easy to read when it's that size.

http://larrysmga.net/8-Wiring/images/MGA%201500%20Wiring.jpg

Jim
JL Cheatham

Vintage Wiring in Melbourne Australia supply the wiring looms complete with numbered tags and a sheet listing the numbers and where they go.
Gary Lock

This thread was discussed between 28/12/2016 and 02/01/2017

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