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MG MGA - Wire Hareness Query

Due to the afore mentioned wiring problems, I have begun repacing the wire harness on my 1500 with the harness offered by Victoria British. (What a disappointment) First, let me admit that I am quite a novice when it comes to wiring, so please, pardon my ignorance. But the VB wiring comes with a rather rinky dink set of plastic panel light sockets to replace the original metalic ones. These new sockets come with a live wire and a ground wire on each. The original sockets have simply a live wire and I assume are grounded by the chassis. Now I have an aftermarket mohagany dash. Do I need to solder a ground wire to the outside of each of the original sockets and attach them to the chassis for ground? Please hold your applause. The turn signal socket is the most mysterious as it is isolated and doesn't appear to be grounded at all like the other instruments which have a black wire terminal.
S. H. Shanks

First of all do yourself a favor and cur the plastic sockets off about 4 inches from the end and use the ones from your original harness. The plastic sockets don't fit as well and can break, plus they don't ground as the originals did. I used some heat shrink wrap on mine and they looked and fit 10 times better.

I can't tell you about the wood dash. At some point you are going to have to ground the lights and your should be able to do that by running a wire from the instruments to the harness or firewall. Not sure what most people with wood dashes do here.

Cheers,
Christopher
Christopher Wilson

Thank you for your reply Christopher. Notes taken.
S. H. Shanks


By "turn signal socket" I'm assuming that you mean turn signal switch. This does not need a ground, when applied it only completes a circuit.

cheers
Bruce
B Suelzle

There is a black ground wire in the harness for attachment to each instrument bracket, thereby grounding the instrument cases. See here: http://mgaguru.com/mgtech/electric/et100b.htm
These aftermarket lamps can then be grounded on the instrument mounting bracket. The original high beam lamp and illumination lamps will be grounded on the instrument shell. The ignition lamp has two wires not grounded.

The turn signal warning lamp and the map lamp were originally grounded on the steel dash panel. With the wood dash you will need to add a ground wire for these two lamps. The replacement plastic bulb holders already have a ground wire that you can attach to the nearest convenient grounding point. Instrument brackets are grounded via the harness black wires. Stabilizing braces on the bottom edge of the dash panel are grounded at the heater shelf.

For grounding the original metal turn signal warning lamp with single wire you could buy a replacement lamp assembly from Moss Motors. See here: http://mgaguru.com/mgtech/faulty/ft012.htm
This assembly has an extra grounding bracket intended particularly for non-grounded panel applications. You could make your own grounding lug. All it takes is a wire end ring lug large enough to go around the thread on the plastic jewel. Original thread was 9mm, wanting 3/8" drill for a clearance hole. The replacement lamp assembly has 8mm threads (very close to 5/16").

The original metal shell map lamp bulb holder is a bit harder to ground on a wood dash, as it was originally plugged directly into the metal dash panel. I'm not even sure how that is intended to mount in the wood dash. I would probably make a diamond shape three hole or square five hole hole bracket from sheet metal to attach to the back of the wood panel with wood screws, then add a grounding wire to one of the screws holding the metal plate.

Alternately for any metal bulb socket you cold solder a grounding wire onto the side of the socket.
Barney Gaylord

Chris is correct, try and find some original. They are rather plentiful on eBay. Another trick I did was to run a ground leg (think it was 10g twisted) from the back of the car to the front. I connected it to the neg terminal of the battery and brought it up along the frame were I brought it up to the firewall connecting it to a ground point behind the dash. I then independently ground each devise to the ground point. It then continued under the shelf lip and down to the starter motor and then along the harness to the front were all fixtures were grounded. Did the same for the back lights, fuel pump, and sending unit. I feel I have a much better circuit with hardly any dimming of the lights and a strong starter motor connection.


WMR Bill

Another question I have concerns the two larger red wires (16ga I think). One is attached to the light switch, one is attached to the fog lamp switch. How do I know which one goes where?
S. H. Shanks

S. H.

You can read through Barney's site or a shop manual with a wiring diagram. However I also recommend these:

http://cgi.ebay.com/ebaymotors/MGA-1600-1959-1962-US-Spec-COLOR-Wiring-Diagram-11x17_W0QQcmdZViewItemQQ_trksidZp3286Q2ec0Q2em14QQhashZitem335500f7a5QQitemZ220469458853QQptZMotorsQ5fManualsQ5fLiterature

I bought one when I wired my car and it was very helpful. I don't know if this is the same seller or not but the reason I like them is they are quite easy to read, laminated, and small enough to roll up and carry in a tool kit.

Cheers,
Christopher
Christopher Wilson

Find five red wire ends on the harness near the lighting switch. Use a continuity tester to poke around among these five wire ends until you find two that are electrically connected (these are the same wire). One of these ends must be connected to the fog light switch.

I have seen some new wiring harnesses where this wire is 16 gauge while the others are 18 gauge. This makes it easy to identify the two ends that are part of the same wire. All red wires are 18 gauge in the original harness (and my replacement harness from 1986).
Barney Gaylord

Barney, thank you for clarifying that for me. By the way, your tutorials on MGA Guru have been quite helpful. I would have never attempted this project without your expert guidance.
S. H. Shanks

This thread was discussed between 25/08/2009 and 26/08/2009

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