Welcome to our resource for MG Car Information.



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 TD TF 1500 - Wiring Harness TD

So I'm starting to replace the wiring harness in my TD. Where do you begin and how do you start. I've contemplated just pulling the dash and then all the firewall stuff and then cleaning the firewall before I start re-assembly. I have a WSM to use as a diagram but was curious do I need to label the old harness? The new one I have is used, and is a cloth wrapped MOSS. George passed it along to me and it is in waaaayy better shape than what is in there. I might have to to some soldering but it better that crunchy wire.

Where do I begin?

Vince - I would suggest laying the harness out on a table or the floor and each end of each wire. then label each end with the place it goes to. This will only take a few hours with a multimeter when the harness is out of the car and make the job of hooking everything up when it is in the car vastly easier. Cheers - Dave
David DuBois

Ditto! Labels are the key.
PJB Brouillette

I have never labeled the cables.....!!! The Moss harness have th correct color codes and if you connect everything correctly you will not have any problems. Start with the complete harness under the dash and starting from there towards the front and then the rear. Installing a new harness is alway a pleasure. so good luck.
Jose Vicente Vargas

I labled mine and also clipped the old one off leaving a couple of inches and all the colors matched up as I connected the new one. Of course if yours is out already, that will not help much. I have the colored diagram that sells on ebay that you are welcome to use. I used it for a 52TD. My email address is thager at if you like to borrow ii I would be happy to send it to you.

tw hager

By the time I got back in the house last night to read this, I already had most of it out. I did label most of what I could while taking it out. The horns, fuel pump and brackets, regulator, cables.... are all off of the firewall. Just have to finish pulling the rest of the wires through and then the rest of the car has to be disconnected.

The harness I got was used so there are no stock labels on them but George did take some masking tape and puts some marks on them. I should be able to get it all back together.

Right now I need to order some grommets for the firewall but not sure how many and which ones are needed for all cables and harness'. Any help on this would be appreciated.

I also uncovered the original glove box but there is a big hole cut into it. I'll need to find a used one or try and repair this one. I might glue some cardboard onto it and the cover with felt. Not like the original flocking but at least I'll have a box.

Hmm what else? The kick panel vinyl that was tucked up and under the dash seems untouched by sunlight and is a bright yellow green. Not sure If I should be matching this or what color but it's something.

I took my old harness and mounted on a piece of plywood, hung it up, rang out all the wires and marked them. It makes for a good reference.


Mike Hart

Uhh that's a plane.

Vince, the easiest way is to find the page in the factory manual with the wiring diagram, and use the color code key there. My scribbled notes were basically what branch went where, not specific connection of course. The turn signal relay on my TD was mounted on the fire wall as on a TF (some Moss kits years ago suggested that)- not origianl but easy to work on. If you mount it there, you may have to feed the under dash part from the outside in, leaving the branches to the flasher and t/s relay outside the firewall. Either way, you may need to file and enlarge the firewall holes little as I think the new harnesses may be fatter than original. Your local parts store likely has a cheap box of about 50 grommets that will last you a lifetime. George
George Butz

Is that a Flybaby?
PJB Brouillette

I marked each end with masking tape and wrote where it went after using an ohm meter to make sure of the correct wire. This was done in the floor with a wiring diagram. By the time I pulled the harness through, connections were easy. The wires will melt in a heartbeat when power is supplied if they are not correct. As soon as I put power on, my hands were under the dash feeling the heat so be careful. Although there was some melting - it was nothing too serious. Good luck.


tw hager

Hi Vince,
Before powering up this harness, after being sure the color codes are all correctly connected, use a good ohmmeter to check for any kind of short from the main feed to ground with all switches off. If you find one, start disconnecting things until it goes away. You then start switching things on to see if you have more shorts that are a result of turning on switches. Filaments will read about an ohm, etc...Then when you power it up for the first time, you should put a fuse in series with the hot side to see if it blows with everything off. I would guess a 20A would be Ok. Another option is to put a 20 watt 10 ohm resistor in series with the hot side to see if there is any drop across the resistor with everything shut off. You can't be too careful because there is no fusing for the lights in the T-series. You have a 50A fuse for the horns and then a 35A fuse for a collection of other items. There are articles on how to add extra fuses to the T-series. I put in about a hlaf dozen of them to various items. I would not advise feeling about in the harness for a hot spot. A good connection to ground will light up the harness in a very short time! Mike Davis
MW Davis

I used painterstape to create a smooth surface around the outcoming wires and used some siliconspray and wobbled the harness through the grommet. Went pretty easy and no need for pliers. See image. When I wanted to connect the wires to the regulator, I noticed they were all going vice versa. So, I took them out again, marked the correct order in which they connect to the Reg and taped them in this order to the main part of the harness. Wobbled them through and now it looks pretty decend, see next post-image.

Huib Bruijstens

Wires to Reg in right sequence.
Greetings, Huib

Huib Bruijstens

I have a different regulator and a fuse box mounted next to it.


OK, maybe I dodged some major bullets here, but in the cars I've wired (four of them) I never tag the harness. I started to once, but realized that it was a useless task.

The only reason I might label the wires is if I were using a very old harness with poor coloring.

When the harness is fitted to the chassis, the correct wires fall to use in the right places. Following the wiring diagram, and making allowances for some early anomolies or custom applictaions, the wiring is staight forward.

I usually solder on the bullet connectors or tin the bare wires after the harness is in place and each wire is cut to length. (I owe Tom Belongia and his lovely Mk II big time for teaching me to be a better solderer) If the turn signal harness has ring terminals, I snip the ring so I can just loosen the screw and slip the terminal in place rather than remove the screw. I do mark the turn signal relay box so I can read the cover easier.

There are some pictures in both the electrical section and the firewall section of my website, including the regulator and fuse block wiring.

Dave Braun

This thread was discussed between 21/03/2010 and 22/03/2010

MG TD TF 1500 index

This thread is from the archive. The Live MG TD TF 1500 BBS is active now.