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MG TD TF 1500 - Wire gauge - Reversing light

I'm planning to install the reverse light soon and need to run wire to the transmission switch (from the power source and then to the reversing light), but not sure what size wire is needed. I assume somewhere between 18 to 22 gauge? While I will likely fit an led bulb initially, I do want the wire run to be of suitable size for a standard filament bulb in the event one is used in the future. Any recommendations?

Jim Rice

18 gauge is OK for LEDs, but if the wiring is to be used with incandescents, I would recommend 16 gauge.
Lew Palmer

Thanks Lew:

One more it advisable to fuse the wire? My first inclination is no...but I've been wrong before.

Jim Rice

A fuse is always a good idea, especially on long runs. But where ia the power fed from? Isn't it already fused?
Lew Palmer


The best way to proceed is to run a green wire from one of the two A4 terminals on the fuse box, then a green/brown wire from the switch to the lamps.
In that case you don't need a extra in line fuse and you follow the British standard colour codes.

J Scragg

Hi John:

That was my plan to pull power off the fuse block. Green wire is no problem....a short run of a single line green/brown wire however may be a bit of a challenge to get here in the U.S.

Jim Rice

If you are really a detail oriented perfectionist have a look at Rhode Island Wiring who I believe (though I have never used them) sell wiring of all gauges and in in all colors with all tracer colors. Now you just have to research what color/tracer BMC used for feeding a reversing lamp.
John Quilter (TD8986)


John S has the wire colors correct. I happened to run across a company in the UK that carries a lot of wire and electrical products for cars, including British Classics.

That also have a handy PDF file (attached) that lists British wire colors and their typical application/use. In their "cable" category, under standard and thin wall, they list the various color wires and sizes available, and they do sell by the meter if you don't need a lot, as well as reels if you need larger amounts. They also have a conversion table for AWG to MM2.

I'll look at RIW now that I know the wire colors. Hopefully they too sell in short lengths and not just big rolls!
Jim Rice

Jim, Try these folks.
PJ Jennings

I added a fuse after the A4 terminal so that it was only usable with ignition is ON.

Previous owner had fed it from permanently live side of side light switch so if the car was left in reverse it was on with ignition OFF.

P G Gilvarry


What amperage fuse did you use?

Jim Rice

5 Amps, good for 60W approx, lamp is 21W from memory. The 5A should provide enough cushion for the initial surge as power is applied.

I have not gone LED yet, as PO used heavy wire, and it only gets used when backing up. I did add a piezo buzzer inside the enclosure to provide aural warning.


PS. I bought a 6 fuse block, mounted it under the dash, fused the lighter socket, USB ports, individual fuel pumps and back up lamp.

2 spare fuses in case I need to add Xmas lights
P G Gilvarry

You'll probably go for overkill. The highest wattage bulb shown in the table on page N.18 is the 48 watt Fog-Lamp. A 48 watt bulb runs at about 4 amps (48W/12V). Backup bulb probably wouldn't have been any higher. Standard tables indicate that 22 AWG wire can readily handle 7 amperes. The 16 gauge wire could handle 22 amps for chassis wiring. With few exceptions, 20 gauge wire can more than handle any wiring in one of our cars. Bud
Bud Krueger

I ran a jumper wire from the tail light circuit to the reverse lamp and use the switch to ground
J Stone

Thanks for all the feedback. Looks like there are a number of ways to run power to the reverse lamp. My question stems from my lack of knowledge on "all things electrical".

What I did not want to do was tap into existing wires IF those were not capable of handling the overall cumulative power draw (albeit for a relatively short time while in reverse) and damage the wiring.

Looks like that's doable without any issue. Using an LED will minimize the draw, but the NO (next owner... likely my son) may end-up using an incandescent if the LED bulb needed to be replaced. Unlikely he would be wondering if the existing wiring was of a sufficient gauge.

Jim Rice

The “usual” reversing light has a BA15S Socket, maximum wattage I have seen is 21W, the amount of time it is in use means that you don’t need jumper cables.

I ran the wiring that I added along the existing wiring under the car, but let me warn you.

If you don’t know what you are doing, buy LOTS of replacement LUCAS smoke, it does leak, fuses help limit the escape, but a burnt cinder MG, is, a burnt cinder MG.

How much can an auto electrician charge? Less than the insurance deductible is my guess.

How much do you reverse, not much, buy a whistle, cheaper and as effective. Or a backup camera maybe?

P G Gilvarry

This thread was discussed between 09/08/2022 and 14/08/2022

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