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MG MGB Technical - Electrical part(s) questions??

I need some assistance please in order to correctly identify electric parts. 1979 mgb roadster. I do have a wiring diagram (Haynes, late version)

The purpose is to clean conections and ground wires too... very "rusty" looking.... but working.

From the front of the engine, slightly above the expansion tank: is this part the Flasher Unit (turn signals?)

Just below the Fuse Box, rectangle piece with wire connections (2) on top... is this the Voltage Stablizer for instruments?

Line fuse(s) two just below voltage this what they are called... I'm not sure of the correct wire colors.. mine don't seem to match the wire diagram in the Haynes book.

Another unit, back by the hood bracket, is this the Starter Solenoid relay?

Can't find the Ignition switch Relay... where is this located? Inside the car??

My plan is to take each unit/wire connections and clean. Plus, clean the area in the engine bay too where they are located. Before I pull any wires loose, I'll take a digital photo/and write notes.

All ground wires will be cleaned, and a new screw(s) used to replace the rusty ones.

Please help by letting me know if I have correctly identified the parts... plus provide some tips you may have.

Kindest regards,
Don 1979 MGB

First, let me heartily recommend that you go to this site, , run by Dan Masters, who has created probably the most easily understood wiring diagrams/schematics for our cars. Go to the Menu on his home page and click on the "stock schematics" button in that menu and download the diagrams you need. You can save them and print them off for free! If you wish you can even take them to Kinkos or the like in your area and have them enlarge them and then laminate them to protect them from greasy hands while you work. This is a fabulous boon for all of us, and you may find it much easier to identify what you have in the car and how each item is wired.

To answer your questions that I might know about, the Voltage stabilizer for the instruments is normally mounted on the INTERIOR side of the firewall up under the dash.

The flashers are usually mounted up under the dash as well. There are two ~ one under the dash, per se, for the signals and another behind the center console for the 4-way flasher circuit.

If the colors on your wiring truly do not match those on the wiring diagram, it may be that someone has rewired at least a portion of your wiring harness, perhaps from a fire or an electrical meltdown.

Hopefully, some other folks here who have 79s will jump in to give you more specifics.
Bob Muenchausen

Use carburator spray on the wires to clean off a quarter-century of grease and assorted crud. You can see the wire colors again.

Dan Robinson

The wire colours should show you which component is which, although each diagram in Haynes is an amalgam of several minor variations (and sometimes not so minor).

The instrument voltage stabiliser, turn signal flasher and hazard flasher are all in the cabin, on the firewall behind the dash. The starter and ignition relays are immediately in front of the fusebox and cylindrical, although either could have been replaced with other types. These could be either way round as the wires all come out of the same part of the harness. Ignition relay should have brown, black, white/brown and white wires. Starter relay should have brown, black, white/brown (or brown/white) and white/red wires i.e. only (apparently) one wire different, but the two white/browns are very different.

There are probably two inline fuses below the fusebox, one for the cooling fan (white/brown and green) and the other possibly for the hazards (brown both sides). However on late cars the cooling fan had a thermal protection device. Whether this was instead of or as well as the fuse, and its location and shape I don't know.

When you say 'hood bracket' do you mean one of the hinges (if so which?) or the stay? If the stay then there is the TCSA solenoid mounted on the pedal bracket that side with yellow/red and black wires.
Paul Hunt 2

Dan... now that is a nice tip to clean-up the wires so I can tell at least what color they are!

Paul... I'll copy and print off your reply. This helps clear up a little of my confusion.

The part that I was trying to determine what it was when I said by the hood bracket must be the starter relay based on the colors you noted for the wires.

Thanks for your help!

Don 1979 MGB.... now where did I set my coffee cup..



78 B---I also have buildup (word?) around the fuse box. Used Simple Greeen around, the area, but was afraid that anything liquid would short the wiring. Thought? I want to clean the engine well, but don't want to sink the ship just to make it look better. Your thoughts?

Careful with that carb cleaner, especially on the paint (and your skin).

"now where did I set my coffee cup"

I wish I could find my glasses! Fortunately I have another pair to help me find them ...

Won't help with coffee cups, although I remember Tom Sawyer losing something he had thrown, then throwing another in more or less the same way and direction and watching where it went. He found both.
Paul Hunt 2

I wonder if Tom Sawyer is looking down at us enjoying our MG's?

Will the carb spray damage the paint??... if so, I'll use some Simple Green (spray on rag and wipe wires). I did this on the spark plug wires and now they look as good as new.

My plan is to use emery paper and clean-up the connections... Simple Green only to clean off ends of wires.


Though it's been 40 years, I remember the particular scene you speak of. I read both Tom Sawyer and Huckleberry Finn in the 7th grade, and had some trouble with the language. Did you need an interpreter to understand some of the dialogue? It's not particularly representative of the "king's English". Dickens still gives me a problem.

Fred Doyen

Hi Fred - I think Dickens gives me more of a problem then Tom Sawyer. Being claustrophobic in natural confined spaces (but not in man made) I well remember the panic *I* felt when Injun Joe got trapped in the caves. Whilst Twain's character's speech could be colloqial it was usually understandable when taken in context, the descriptive text was very plain. A modern writers such as Stephen King is much more 'inventive' both in speech and description, whereas with John Grisham 'color' seems to be one of the few departures from 'English' English. I've just started reading 'The Seven Pillars of Wisdom' by T E Lawrence and that is pretty hard going even though it was only written in the 1920s. One amusing corrollary with Mark Twain is that Lawrence took a delight in spelling Arabian place and personal names in a variety of ways as correspondence between him and his reviewers and publisher shows, and of course there is the famous Twain quote "I don't give a damn for a man that can spell a word only one way".
Paul Hunt 2

If worried, you can always disconnect the battery when doing electrical work.

Paul --- I am presently reading The Thin Red Line - about a number of your chaps during the Crimean War. 'Makes Iraq look like home leave.

Dan Robinson

... and always by disconnecting the battery ground strap first and reconnecting it last, this is regardless of polarity.

Dan - which version? I understand it has been somewhat revised from a defeat into something of a success :o)

My father-in-law's Regiment - The Worcester Yeomanry - made the last British Cavalry sabre charge in 1917 in the Sinia Desert which was part of the ending of 500 years of Turkish rule of Arabia, and where T E Lawrence more or less came in. 181 mounted men charged 24 field guns head on and cut down every one of the men manning them, then turned on the 20,000 'other ranks' and scattered them. All in 20 minutes.
Paul Hunt 2

This thread was discussed between 20/10/2006 and 26/10/2006

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