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MG TD TF 1500 - Relays

Will be beginning wiring installation soon and have been thinking of adding relays to the circuits for headlights, foglights, horn and tail lights. Wonder if others have done this and what the proper type and source might be? Thanks

Bill
Bill Reid TD4618

Headlights, Fog Lights and tail lights, IMHO, better to change to LED.
No relays needed, then.
Horn, perhaps, Yes.

Jim B.
JA Benjamin

I have used LEDs on other cars and bikes and they work well, but already have an investment in the old style stuff. Seems too that LEDs impact the early post war look of this old car.....I’m good with using newer technology if it can be hidden (electronic ignition, etc), but LED lights are a glaring departure (sorry for the pun).

Bill
Bill Reid TD4618

No relay for headlights because consuption is only
36+36 (headlight)+6+6 (tail lights) = 84 W hence a current of 7 A. I think that the Lucas PLC6 rotary switch can handle such a current
But I installed a relay to protect the expensive horn push. Consumption of horns is 11A per horn.
Furthermore, they feature an inductive load and can produce high sparks on contact points at button release.

I used a vintage lucas 6RA which can handle up to 20 Amps.
I already had it but you can use any modern reference that is suited for 20 Amps.
The relay is fixed near the fuse box.

https://www.autoelectricsupplies.fr/product/729
Laurent.
LC Laurent31

A couple of years ago I decided to check out the effective gain from installing relays in the headlight circuits. I measured the voltage across the lamp terminals in each condition. It turned out that there was virtually no gain. The only expected gain was from reduction of the voltage drop across the light switch due to the current of both lamps versus the voltage drop across one relay contact. However, the drop caused by the additional wiring (and the various connections) ate up the expected gain. I took the relays back out. BTW, I don't think there are any inductive loads in the lamp circuit. The lamps present a resistive load, though variable with lamp temperature. Bud
Bud Krueger

I know you said you think that LEDs impact the early post war look, but it is a small price to pay. Their brilliance enhances the visual safety factor exponentially. IMHO the use of LEDs for gauges, marker, tail/stops and even flood/Fog lights over the dim and barely visible incandescents is a no brainer. This is especially important in inclement weather conditions.

Bill Chasser
TD-4834
W A Chasser

Installation of relays and LEDs both have positive outcomes.

Location of the relays in close proximity to their loads and the gauge of wiring used for both the supply to the relay and the load dramatically affect their performance.

Selection of a relay with inbuilt fuse protection decreases the ability to create Lucas smoke.

The increase in brightness of LEDS verses incandescent globes is an asset that should be mandatory for safety reasons. This falls into the same category as maintaining the use of white and red indicator lights on a vehicle.

Graeme
G Evans

I put relays behind the PL700s on the car to protect the switch on the dash. The switch stays cool now, before the relays, it was uncomfortable to put your finger on the back of the switch as it was quite warm.
PJ Jennings

Excellent discussion!

Bill
Bill Reid TD4618

Talking about wiring. have a look at the whole article :
https://ttypes.org/making-your-own-mg-td-wiring-loom/

Laurent.
LC Laurent31

I believe you can also find a write up by the late Dave DuBois regarding protecting lighting circuits with relays on the “Original MGTD” website. Although the brief article is related to brake switches it may be worth a read. Tap on the Details section and scroll to the article

Bill Chasser
TD-4834
W A Chasser

I’m going with LEDs....
Bill Reid TD4618

This thread was discussed between 03/11/2020 and 06/11/2020

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