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MG MGB Technical - MGB Wiring Questions

I am reinstalling the dash in my 77 MBG and have am confused as to the attachment of a few wires. I have studied the wiring diagram in the manual but am still lost. I have three issues.....HELP!!!!

Issue 1: Four wires exit the harness near the wiper motor. 2 are green with a brown or orange stripe; 1 is brown; one is green. Given the ends it would appear as if they should go to the two small rectangular boxes mounted on the firewall just left of the wiper motor. The poles of the boxes are marked with the letters L and B. Is this where these wires go? If so which poles do the wires attach to on the boxes?

Issue 2. A short distance from that point four wires exit the harness. One is a single white with a red stripe and has a small black something or other attached to it. The other has two white with red stripe wires also with the same type of devise attached to it. Near them are other wires, 1 is green with an orange stripe and there are two greens with an orange stripe. They have connectors that would appear to fit onto the white/red stripe wires. Do the green/oranges stripe wires attach to the white/red stripe? If so does the single green attach to the single white with the doubles attaching or do the singles attach to the doubles?

Issue 3. At the same point on the harness where the white with red stripe wires talked of above exit the harness there are several green wires. All are solid green with the exception of one which is green with a white stripe. Most of the solid green wires would have been left connected not having to be unconnected to remove the harness from the car. However, there is a single green wire with a female connector and one single green/white stripe wire with a round male connector unattached. Do these two connect or are they to be routed somewhere else and if so where?

I know this is a long post and I apologize I sincerely hope a fellow MGer can assist. Thank you so much for your indulgence.
J Fleshman

Hi,

I can't help you directly with your problem, but this web site, www.advanceautowire.com has decent wiring diagrams, that can be easily understood, and with all wires correctly coloured.

Herb
Herb Adler

On a 77 the five wires for the wiper motor should be in a multi-pin conenctor that just plugs into the socket on the motor - green, brown with a light-green stripe, red/light-green, blue/light-green and black.

The box marked L and B is the instrument voltage stabiliser and should have a green wire on B and a light-green/green on L. This box should be screwed to the firewall.

The green/orange should go to one side of an isolation diode which should have white/red wires on the other side. These should be male and female so you can't get them the wrong way round on the diode.

Two other white/reds should go to one side of another isolation diode with green/blacks the other side, again male and female spades. These two white/reds are electrically the same so it shouldn't matter if you get them jumbled up, but each set that goes to each isolation diode should be a separate tail with its own wrapping coming out of the main harness.

The only green/white wires should be associated with the right-hand indicators, however there are many green wires with different coloured stripes, both 'standard' green and light green so you need to be clear exactly what colour it is, we can't see it. Mostly the wires come out of the harness by the component they are connected to, so aren't that difficult to decide what goes where. Male spade connectors are quite rare, male bullet connectors usually plug into a 2 or 4-way bullet connector and continue on the same colour, there are several of these behind the dash.

Brown and light-green wires go to the hazard flasher, and green and light-green/brown to the indicator or turn flasher, and the two flasher units were pushed into spring-clips side by side low down on the firewall inside the cabin on later cars. However these two light-green/browns are *not* electrically the same so you must get them on the right flasher unit, indeed you must get both wires onto the correct flasher unit as the one for the hazards is quite different to the other. Again usually each pair had its own wrapping for a short distance coming out of the main harness.



P Hunt

thank u herb for your response. it helped a great deal.
J Fleshman

In addition to Paul's great response I can add:
The red/white with the diodes on are for the braking and seatbelt system and the EGR service counter.

The twin red/white should mate with a green/pink double for the EGR counter, the single red/white should go to a double green/orange for the braking and seatbelt system.

The green/white wire sounds like the aux circuit for the radio/ICE system. It should be more white than green, rather than the indicator circuit which is more green than white. Looking at the thickness of the colour bands should help you decide which is bigger and hence which is the main colour.

Could the single green at this point go to power the tachometer?

Hope that gives a little more insight!
RoadWarrior

The green/white wire might go to the indicator light on the dash. Barrie E
B Egerton

Ah yes, white/green (not green/white) is the unfused accessories wire from the ignition switch. This should only appear behind the console (i.e. not near the wipers), and is not used (but should have a bullet connector on to insulate the bullet) unless you have a radio or some other accessories position powered device fitted.

The indicator lights, like the gauge illumination lights, *should* have the bulb holders soldered to them, i.e. no bullets or spade connectors.

BTW Barrie, came across this in a TV documentary about Holden cars on the Qantas flights, made me smile
http://www.youtube.com/watch?v=VGW-WX77zjY
P Hunt

Does anyone have an idea how long it should take to replace a full wiring harness in a B ....?

Cheers,
Mark.
M T Boldry

Mark

That would depend on how complete the car is - i.e. whether engine, gearbox and dash are in place.

Easier than a midget in one respect, as the main front to rear loom goes under rather than through the car. Also depends whether it has the separate dash loom or not.
Dave O'Neill 2

Dave, the car is complete and running, it has come into the Classic Car Clinic with various electrical faults which when you se the present wiring harness, is not surprising..!

It's such a long time since I got involved with a B to this extent, I had forgotten about the under-car routing of the harness.

Mark.
M T Boldry

The rear harness (separate to the main harness) is a beggar and will take several times longer than the main harness. If you know what you are doing and are able to remove the old and refit the new without much head-scratching you should do the main in a day once the dash has been pulled forwards. 77 and later cars are easier as they have a separate dash-harness which can be attached with the dash completely out of the car, making lots of space to position the main harness. There is also a gearbox harness, which is a fiddle to attach to the gearbox switches, usually requiring the rear crossmember and gearbox to be lowered on a jack and the tunnel console (where fitted), carpet and panel that is under it removed.
Paul (too many Pauls own MGBs) Hunt

This thread was discussed between 04/03/2010 and 08/03/2010

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