Additional masthead lights and towing light; tow length matters.
Paragraph (a): Power-driven vessel towing
A power-driven vessel when towing shall exhibit:
(i) instead of the Rule 23(a)(i) or (a)(ii) masthead light, two masthead lights in a vertical line (forward or aft): three such lights when the length of the tow (from the stern of the towing vessel to the after end of the tow) exceeds 200 m;
(ii) sidelights;
(iii) a sternlight;
(iv) a towing light in a vertical line above the sternlight;
(v) when the tow exceeds 200 m, a diamond shape where it can best be seen.
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Bow / head-on
Port side
Starboard side
Stern / overtaking
Rule 24(a) Towing: tow ≤ 200 m
Bow / head-on
Port side
Starboard side
Stern / overtaking
Rule 24(a)(i) Towing: tow > 200 m
Wording follows the International Regulations as printed in the US Coast Guard Navigation Rules handbook (2024), with British spelling, and is shortened in places. Download the rules
Read the whole of Rule 24 on one page
Paragraph (a): Power-driven vessel towing
A power-driven vessel when towing shall exhibit:
(i) instead of the Rule 23(a)(i) or (a)(ii) masthead light, two masthead lights in a vertical line (forward or aft): three such lights when the length of the tow (from the stern of the towing vessel to the after end of the tow) exceeds 200 m;
(ii) sidelights;
(iii) a sternlight;
(iv) a towing light in a vertical line above the sternlight;
(v) when the tow exceeds 200 m, a diamond shape where it can best be seen.
Paragraph (b): Composite unit
When a pushing vessel and a vessel being pushed ahead are rigidly connected in a composite unit they shall be regarded as a power-driven vessel and exhibit the lights prescribed in Rule 23.
Paragraph (c): Pushing ahead / towing alongside
A power-driven vessel when pushing ahead or towing alongside, except in the case of a composite unit, shall exhibit:
(i) instead of the Rule 23(a)(i) or (a)(ii) masthead light, two masthead lights in a vertical line (forward or aft);
(ii) sidelights;
(iii) a sternlight.
Paragraph (d): Second masthead light
A power-driven vessel to which paragraph (a) or (c) applies shall also comply with Rule 23(a)(ii): the second masthead light, abaft of and higher than the forward one, required at 50 m or more and optional below.
Paragraph (e): Vessel or object being towed
A vessel or object being towed, other than those in paragraph (g), shall exhibit:
(i) sidelights;
(ii) a sternlight;
(iii) when the tow exceeds 200 m, a diamond shape where it can best be seen.
Paragraph (f): Groups towed or pushed
Any number of vessels being towed alongside or pushed in a group shall be lighted as one vessel:
(i) a vessel being pushed ahead (not part of a composite unit) shall exhibit sidelights at the forward end;
(ii) a vessel being towed alongside shall exhibit a sternlight and sidelights at the forward end.
An inconspicuous, partly submerged vessel or object, or combination of such vessels or objects being towed, shall exhibit:
(i) if it is less than 25 m in breadth, one all-round white light at or near the forward end and one at or near the after end, except that dracones need not exhibit a light at or near the forward end;
(ii) if it is 25 m or more in breadth, two additional all-round white lights at or near the extremities of its breadth;
(iii) if it exceeds 100 m in length, additional all-round white lights between the lights in (i) and (ii) so that the distance between the lights does not exceed 100 m;
(iv) a diamond shape at or near the aftermost extremity of the last vessel or object being towed, and if the length of the tow exceeds 200 m an additional diamond shape where it can best be seen and located as far forward as is practicable.
Paragraph (h): When lighting is impracticable
Where from any sufficient cause it is impracticable for a vessel or object being towed to exhibit the paragraph (e) or (g) lights or shapes, all possible measures shall be taken to light the vessel or object towed, or at least to indicate its presence.
Paragraph (i): Towing a vessel in distress
Where from any sufficient cause it is impracticable for a vessel not normally engaged in towing operations to display the paragraph (a) or (c) lights, she shall not be required to exhibit those lights when towing another vessel in distress or otherwise in need of assistance. All possible measures shall be taken to indicate the relationship between the towing vessel and the vessel being towed, as authorized by Rule 36, in particular by illuminating the towline.
In plain words: a yacht towing a disabled boat home need not carry towing lights, but should light up the towline.
A training aid, not the official text. The COLREGs are an IMO convention, and your national authority publishes the version that applies in its waters. Check the rules themselves before you rely on them at sea. Download the rules.