Tech: Moss Wiring Harnesses

If you think you are in the market for a new wiring harness, there are a few things you might want to consider before making a purchase. We’d like the opportunity to explain what Moss carries and why, and give you some pointers to guide you through the process.

Before you do anything, even before you log onto MossMotors.com to shop, remember this mantra: Don’t Throw Anything Away. You never know exactly what a previous owner may have done.

Consider Repairing instead of Replacing. If you have just one spot of damage, you could repair that one area instead of ripping into your entire car for an full harness replacement. Repair is usually much easier – on both your time and your wallet. Moss carries the correct wrapping tape so once a repair is complete it will look period correct. Of course an older car like a T-Series or MGA that has never had wiring work done might be a great candidate for a complete harness replacement, or any car undergoing a full, concourse restoration.

Our own Kelvin Dodd from Tech Services recalls a 1979 MGB LE he bought, knowing at one point in its life it had suffered from a fire in the engine compartment. Thinking he might be able to simply splice into the existing harness for repairs, he unfortunately discovered the previous owner had already “completed” a full harness replacement; but had hacked into it so poorly, he was forced to do another full harness replacement himself, using a Moss supplied kit. (The helpful mantra above, was suggested by Kelvin, as a result of this harness replacement job.)

We believe that the kits we offer to you are the best on the market today. These are hand-made specifically to each application, and (as described in detail below) using modern enhancements for safety while retaining a period-correct look. Trained specialists in the UK build these kits for us and work with us for correct specifications.

Speaking of period correctness, Moss carries certain kits that we feel our customers would be most interested in. If you’re finding we don’t have the exact harness you need we can special order a kit for you. Moss UK carries the Euro-spec harnesses, which we can order for Canadian customers. However the majority of our customers will be happy with exactly what we’ve chosen to place on our warehouse shelves.

Very early cars were built with wiring that was not modern, and could be unsafe. Wires were insulated with a woven, cloth covering and color coded, and then the bundle was also covered in the same woven cloth covering. This is not to modern standards, it is considered unsafe, and no one is making reproductions like this anymore for safety reasons. That being said, however, Moss Motors offers reproductions of the early harness have the look of the originals but with the safety of modern harnesses. The individual wires are first PVC insulated before the lacquer braid is added. A high quality and great looking woven cotton cloth encases the harness.

 

Early Harness - Lacquer Braid Insulation with Woven Cotton Cloth Covering

Early Harness – PVC and Lacquer Braid Insulation with Woven Cotton Cloth Covering

Early Harness - Close up of Lacquer Braid Insulation and Woven Cotton Cover

Early Harness – Close up of Lacquer Braid (which covers PVC insulation) and Woven Cotton Cover

Later cars had PVC insulated wires and the bundles were wrapped in the woven cloth material. Reproduction kits are available in this style, good for an owner wanting to keep his car period-correct in looks.

 

Later Harness - PVC insulated Wires with Woven Cotton Cover

Later Harness – PVC insulated Wires with Woven Cotton Cover

Close Up - Later Harness with PVC insulated Wires with Woven Cotton Cover

Close Up – Later Harness with PVC insulated Wires with Woven Cotton Cover

 

 

Even later cars had PVC wires and their bundles were wrapped in PVC tape wrap; much more modern. We carry these kits as well.

Late Harness - PVC insulated Wires with PVC Wrapped Cover

Late Harness – PVC insulated Wires with PVC Wrapped Cover

Close Up - Late Harness with PVC insulated Wires with PVC Wrapped Cover

Close Up – Late Harness with PVC insulated Wires with PVC Wrapped Cover

 

For most cars we cater to we offer both options, because the cost of the complete vinyl kit is usually less than the cloth bundled kit and might be a more favorable to a budget. The cloth kits can be “expensive” but we recommend them for TRs and Big Healeys where concourse looks are very important. For some cars we might not offer the full vinyl kits simply because they aren’t period correct and we believe our customers just aren’t interested in that vinyl option.

Another twist to consider is lamp sockets and plugs or terminations. At one time the original screw-in style of sockets simply became unavailable, not made any longer. Harness manufacturers began putting the modern style sockets on their harnesses, but later the old style sockets became available again. Some of our kits have the modern style and some the old style. Another plus for remembering the mantra of not throwing anything away – you could splice in the bulbs your car came to you with. However, know that many of the old style bulbs can be tough to find. You might also find a situation where you need to use an existing plug from your car. Don’t throw anything away – for example with MGB electric cooling fans, the harness we sell is correct, but the replacement fans themselves are supplied with an incorrect plug. More splicing will be necessary.

Know that many cars were built with multiple, separate harnesses. When you’re ready to buy a “kit,” keep in mind you may need another kit as well. An informed shopper needs to pay attention to those extra bits. For example, cars with the hi-lo headlamp dip switch on the floor – that particular harness is separate because of RHD or LHD build differences. You would need to add that to your kit order. Another example is on the late 77-80 MGB headlamps. The replacement switch originally came with its own harness, when you were replacing the switch, but that switch now comes alone and would additionally require a harness.

Hopefully this has answered quite a few of your questions about when to replace an entire wiring harness and why you might choose certain parts over others. We hope you know you can always call our Sales or Tech staff to get help with specific issues. And we truthfully want your feedback after you’ve done your installation. Knowing what cars are still out on the road, and any special modification you needed to do to our harness to make it work for you, helps us to stock correct kits. For now we are offering you the best kits available and we hope your decision is now more informed and confident!


'Tech: Moss Wiring Harnesses' have 18 comments

  1. March 23, 2018 @ 8:44 am Mel Hoover

    Very good information on replacing a new harness!

    Reply

  2. February 19, 2019 @ 10:29 am Steph

    MOSS ought to insert a “tree” diagram in this explanation for those who want to repair their harness

    Reply

  3. May 4, 2019 @ 1:13 pm Milo

    How about a diagram for all the connections?

    Reply

    • November 1, 2022 @ 12:15 pm Bennet Aiken

      Definitely should include a colored diagram with the harness chosen!! There are some on the internet, but they may (and I found that most are not!) not matched to the harness you are ordering from Moss! Great suggestion Milo!

      Reply

  4. August 27, 2019 @ 1:34 pm Kevin Becker

    I have a 1954 MGTF and ordered both the main harness and sub-harness for under the dash. The main harness matched the wiring schematic perfectly so I’m ready to go with that. BUT, the sub-harness does not match at ALL with the schematic so I don’t know what wire goes where. Any help would be appreciated.

    Reply

    • May 2, 2021 @ 12:05 pm Russ Van Tine

      I agree….. I have the same problem with the sub-harness for my MGTD! Since the sub harness is for extending the wires under the dashboard, the colors should match the colors on the main wire harness as well as the wiring diagram. For example, there is a short blue wire in the sub harness but there is no way to know where it goes under the dashboard based on the wiring diagram (the wire diagram has a long blue wire from “H” of the ignition switch to the “dipper switch” but that wire is already in the wiring harness !!. I can tell you that some of the colors are correct and match the wiring diagram (for example on the MGTD, there is a short brown wire on the sub harness that goes from the ammeter to the inspection socket…. that matches the wiring diagram. The sub-harness also has a white/red wire (long wire) …. that is actually wire number 44 on the MGTD wiring diagram which is used for the under-dash panel lights. (#44 is not listed on the wiring diagram as a color). On the MGTD the white wire goes from the ignition switch port “IG” to the ignition warning light…. that matches the wiring diagram. It would be better if a supplemental wiring diagram was included in the sub-harness shipment. I do not know if any of this will help you!

      Reply

  5. May 15, 2020 @ 1:01 pm John D Disney

    Is the wiring harness a “plug and play”? I ordered a kit from another company and what they sent me was nowhere close to what I need. After many hours of attempting to make it work, I am no closer than I was when I started. I’m not a certified mechanic but have been around cars all my life, but being about sick of it, I want my car on the road.

    Reply

    • March 10, 2021 @ 10:10 am Kevin Carroll

      Hi. I just received p/n 356-917 for my 1976 MG Midget. The end that goes into the engine compartment has male and female plugs. How do these attach to the fuse box? Help! Thanks – Kevin

      Reply

  6. June 17, 2020 @ 1:25 pm Jerry Yarbrough

    Hello,
    I am looking or the installation instructions for the complete wiring harness for 1960 Bugeye. You say it is here but I am unable to find them.Jerry

    Reply

    • February 1, 2022 @ 8:28 am Michael Flynn

      Jerry
      Did you ever get a sprite diagram? Before I undertake a replacement for my ‘59 Bugeye, I am hopeful there is a good diagram out there.

      Reply

      • August 4, 2022 @ 5:00 pm Art Van Houten

        How about some instructions on which piece of the wire harness goes where? The MGAguru has some pictures but the resolution isn’t good enough. Some of us are building cars from scrap and need guidance…

        Reply

  7. February 9, 2021 @ 10:27 am Haig

    A warmed loom is more flexible.

    Reply

  8. October 20, 2022 @ 5:24 pm Russ

    Honestly all I need is the female connector for the Hazard switch.. hate to spend $300 on a sub harness for just that..

    Reply

  9. February 6, 2023 @ 7:36 am Thomas Knight

    I have a wiring harness that I thought was for my MGA 1600, but the color codes are wrong. There are no yellow wires in the loom. There appears to have the correct colors for the windshield wiper motor, no wire leads for the high beam button. All the control box colors are wrong lots of blue wires. Is there any way to ID this loom.
    tHANKS FOR ANY HELP you can give me

    Reply

  10. September 26, 2023 @ 9:33 am George Schultz

    I started down this path. It’s a quagmire. To start with it was a 1976 MGB 4 cyl. converted to a Buick 1963 aluminum block V8 with Pertronix guts to the distributor, a Delco Remy DN460 (which the Delco tech support manager told me did not exist); “They never made a DN460”. The conversion was done reputedly by Peter White Motors in Vancouver WA. My experience with the car started in 2012 after the passing Richard Freeman (Dick) a long time winner of Forest Grove Oregon’s Concourse De Elegance. His 1967 Red MGB a perpetual winner. With Dick’s passing his estate found 14 Little British Cars in monthly storage throughout Portland OR and Vancouver WA. We bought this one to help out a friend who was settling the estate. The estate was being sucked dry by the cost of the storage fees. Later, another friend tried to help polish up the car, and looked into why I had to back off the ignition key to get it to run. He discovered the Delco DN460 plugs were rotten – their plastic had disintegrated. The fire that resulted from touching the alternator plug was limited to the main wire harness, most every brown, white and green wire on the right side fender by the fuse box was melted at multiple spots. .. I took the path Moss recommended and did the one off repairs to as many wires as I could find. You’ll never find them all. I found there’d been an arc welding cut between the two sides of the radio console ; That the wires up in the right side of the steering column had – what can only be called gnawed at by a herd of mice. I ended up on this page thinking I might try the alternative route; replace the whole harness. At least then I thought the truncated wires in several of the plugs under the left side of the dash would get fully restored to Moss’ new harness plugs. I have had the car repaired enough on four occasions to get it to start. I’m about to try my fifth. At this point, with all the wire, connectors, heat shrink, test tools bought and research hours, cuts and bandages,; my wife’s comment is, that patching the wires is a “sh_t” show( abbreviated- in hopes to remove the vulgarity). We’ll never recoup the initial cost of buying the car which we did to help our friends who were executing the estate of Dick Freeman. Anyone who is interested, the car is able to run. If anyone wants to volunteer a whole new harness, I’ll video the whole process; that should be more productive than reading through Porter’s restoration book (Haynes). I’m thinking there are a lot of people who got started on doing the complete rewire, the ” RE-Do”.
    Dear Dick Freeman, rest in peace.

    Reply

  11. April 9, 2024 @ 5:22 pm Mark Sargent

    I bought a 1967 TR4A that a restoration had been started. It was a body off and the guy lost interest after 20 years of working on the car. There was some patch work done to the harness but I thought I could get it going by checking and rechecking the work. Wrong. I just smoked the main harness. #$@K!! I guess it is part of the process but damn, I had head lights yesterday but today I have melted wires. Thank God Moss has new and improved harnesses in stock. $450 isnt bad either. I just have to convince my wife it is a good deal……WISH ME LUCK!

    Reply

  12. April 29, 2024 @ 8:32 am Jack Schaible

    I purchased a 1971 TR6 with a Moss #356-748 wiring harness with bayonet bulb connectors. The harness is new but was purchased in 2007.
    Can you supply a wiring diagram for this kit?

    Reply


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