MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGA - New Wiring Harness

Hello everyone,

I popped a re-built 1800 MG engine into my MGA which has no wiring in whatsoever.

I am about to launch into fitting a new wiring harness - is this something that I could feasibly do ? Any tips on simplest methods, anything I have to bear in mind with diff engine/ancillaries in ..?

Thanks

Aleks
Aleks Stojanovic

The only difference an 1800 will make to the standard MGA wiring loom is if it's the later 5 bearing engine without the mechanical tachometer. In this case you will need to wire in an extra cable or two for an electronic tacho.

Steve
Steve Gyles

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 goo 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

When you have finished installing the loom do not be tempted to test the system by using the battery. It can push far too much current into the system and mistakes are likely to be found by lots of smoke rising and possibly the need to buy another loom.

You can test most of the system using an old fashioned battery charger but beware that the output of these is not smooth DC and will possibly effect the operation of things like the regulator and flasher unit. It will find any short circuits by the ammeter going hard over. Many modern battery chargers need to "see" a battery on the end of the leads before they deliver any current so are not suitable. I use an old bench power supply which is current limited at 3 amps. Obviously this will not power the headlights properly but will check just about everything else.
Malcolm Asquith

Good time to add fuses and relays. I found a fuse holder and a terminal block both with holes for mounting that matched the spacing of the holes in the fire wall for mounting the regulator. So I did not have to drill any new holes, terminal block is on the engine side and is used to make all the connections where the regulator had been ( I have an alternator).
Fuse holder has fuses for lights, high beam, low beam, wiper, fuel pump.
I put a second terminal block on the drivers side (same holes for regulator mounting on a RH drive) I used this block to make the connections that are crowded onto the ignition switch.
I mounted relays for the high beam, and low beam under the dash. The relay for the brake light is on the fire wall.
Use the correct color coded wire from the old harness as you wire the new components.
Steve
S E Bryan

I also used the fog light switch to control the power to the ignition coil and the fuel pump. This way power can be turned off to these when you are working on the electrical system. It also can be an anti theft switch, hidden in plane sight, when you park the car.
Steve
S E Bryan

This thread was discussed between 25/06/2015 and 26/06/2015

MG MGA index

This thread is from the archive. The Live MG MGA BBS is active now.