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MG MGB GT V8 Factory Originals Technical - Advice on Final Wiring Connections

Hello Everyone,

I am in the final throes of connecting my wiring and I wanted to seek some advice regarding connections.

I have trawled the archives and pored over my wiring diagrams (at least 6 of which seem to relate to my car in some small way!), and solved most of my problems myself (I hope). But have a few loose ends left, and a few things I need to check with some knowledgable people as I dont want to fry myself or the car.

Kit
===

Car: November 1972 GT, much played with loom by PO.

Engine/Starter : SD1 Series 2 V8, with the later distributor - no separate ballast resistor, and has the little box of tricks on the side of the distributor itself which has a thin white wire and a thin black/white wire coming from it.

Alternator : New, type CA305IR (if anyone's interested). Has 'W' post, B+ post, D+ spade terminal, 2 x B+ spade terminals. Puts out about 70 amps.

Questions
=========


1. The bit of the loom which drops down to the starter has two thick brown cable/ring connectors and a thinner white/brown wire with a spade connector.

I have joined the two brown wires to the same post as the battery lead, and the white/brown wire to the spade connector on the solenoid. Those seem to be the only places for them and they all look to be joined together on the same circuit anyway.

Is that right?

2. The bit of the loom for the alternator has 1 thick brown wire, one thin brown wire, and about 8 inches back along the loom a thin (Cream/yellow/very dirty white?) wire.

I assume that the two brown wires can go to any convenient B+ terminal (they are all on the same circuit aren't they?).

I also assume the dirty white wire is for the ignition/warning light and goes to the D+ terminal.

Am I correct here?

3. Coil (from orignial engine so matches distributor etc).

This has the two smaller spade terminals marked '1' and '15'. From my notes I think the white wire from the distributor goes on to the terminal marked '15' and the black/white wire from the distributor goes to the terminal marked '1'. I can't confirm it as my SD1 wiring diagrams don't seem to cover this variation.

Is this correct?

4. Tachometer

Where does this figure in the set up? My various diagrams show it either wired into the coil or the alternator. The chap at the auto electrics shop said I could use the 'W' post on the alternator. But most diagrams seem to have it coming from one of the terminals on the coil. There is a second white wire snipped off at the coil terminal (the first goes to the distributor) but I don't know where this went orginally.

How/where do I wire the tacho up?

A big bunch of questions and lots of details I know (!) but I'd really appreciate any input.

Regards and thanks,

Liam
Liam H

Better add - it's a carb set up not EFI.

Liam
Liam H

Liam,

I don’t have a complete answer and mine is different to yours but the following might help sort out what you have.

1) One of the two thick brown wires is the supply the fuse box/un-fused circuits, the other goes to the alternator, the thinner white/brown wire is from the starter relay (or direct from the ignition/starter switch if you don’t have a relay) to the starter motor solenoid. What you have seems correct.

2) I don’t know which alternator you have but the thick brown wire should be connected to the B+ spade/post. The thin brown (or is it brown/yellow?) could be for the ignition warning lamp. The cream/yellow/very dirty white is possibly the ignition supply to the coil – what is the other end of this wire connected to?

3) & 4) It sounds like you have a Range Rover distributor, I might be wrong but as far as I know this type was never fitted to the SD1 (my ’83 Series 2 had a separate amp under the coil but no ballast resistor). There should be a black/white wire from the tacho, this connects to the black/white at the coil (-). The second white wire snipped off at the coil (+) should be connected to the cream/yellow/very dirty white at the alternator, or wherever you have the ignition supply, if the dirty white isn’t it.

It doesn’t matter if it is Efi or carbs, the ignition system is separate and the Efi is only connected at the coil (black/white) for the engine pulse signal.

Geoff
Geoff King

Hi again Geoff,

Thanks for the input, nice to hear from you again.

Last night I spread out every wiring diagram I had (8 or 9) and trawled every post on the group about anything to do with ignition systems.

By a process of elimination I was left with what you describe but its reassuring to hear it from someome else

I think you are right about the cream/yellow/very dirty white wire and finding out what it is connected to, hopefully it is a live feed from the ignition side of fusebox.

BTW the whole lot dizzy included came from the SD1 donor - one of the very last ones. I think the dizzy is 35DLM8.

A couple of other issues have arisen - I have an ignition siwtch with 5 terminals and no numbers! I saw some other posts here with the same problem so I have just spent a wondeful hour crammed into a half built car in the rain and dark holding a torch, and circuit tester probes in my mouth, wiring diagram and my notes in one hand, and turning the key with other!

By testing connectivity I think I have the terminals identfied but:

1. There are two sets of paired white wires, and my labelling from dismantling last year suggests that one of the pair shares the same spade as the white/green accessories wire - does this make sense?

2. My Bosch coil only has '1' and '15' on the terminals - do you know which is positive?

3. Is the fuse box positioned so the numbers 1,2,3 etc start from the top or the bottom? I have them running from the bottom but I know that 1234 are set up differently from the rest.

4. Every terminal on the fuse box seems to run to earth!! I hope I have it upside down and that explains it. I hope I don't have a burnt out earth wire somewhere in the loom.

5.There is no black/white wire coming from the tacho, only white. I'll cross that bridge when I come to it.

You have some lovely weather heading up to you tonight!

Liam

Liam

Liam, the bridged fuses are for the side lights & are usually at the top.The other two are for the white/green cct. & the brown/purple cct.It doesn't really matter which fuse they use as long as the ccts. are not crossed. Barrie E
Barrie Egerton

Hi Liam,

I must have slept through the bad weather; it’s no worse than usual here.

Can’t help with the ignition switch – mine is from a ’77 B. Or the coil – mine is a Lucas.

Fuse box:
1 & 2 at the top.
Red/Green to 1. (1 & 3 are bridged). Red to 2 (left sidelights) & 4 (right sidelights).
White to 5, green to 6.
Brown to 7 purple to 8.

The wire from tacho should be white/black, so there is something a bit odd there.

Geoff
Geoff King

This thread was discussed between 20/11/2006 and 23/11/2006

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