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MG MGB Technical - Headlight relay system

Thinking about upgrading my headlights to something a bit brighter. I have read the archives and it looks like adding a separate light wiring system with relays is an important part of any headlight upgrade that is going to require more power.

I see that both Moss and VB have wiring harness systems. I assume that there are others out there also. (Some of you probably built your own).

What have others used and recommend for headlights and harness? I am looking to increase the front lighting for my 67 BGT. With our Wisconsin deer and their love of running out into the road, I would like a bit more visibility at night.
Bruce Cunha

Bruce - Do you have book, Classic MGB Electrical Systems or even his later book Classic British Car Electrical Systems? Both of those books cover adding relays to the headlights (and Daytime Running Lights). If you don't have either book, e-mail me at SUfuelpumps@donobi.net Cheers - Dave
David DuBois

Highly advisable to add fuses as well, one per filament. If you improve the flow of current to the lamps you will burn the wiring that much faster if you get a short. If you choose to fit a fusible link to the system as a whole remember that you may flash your main beams while the dipped beams are on, so it needs to be man enough to take more than all four filaments. You might like to have a look at http://www.mgb-stuff.org.uk/electricstext2.htm#uprated
Paul Hunt

Thanks Paul. Appreciate the link. I was planning to add fuses. I try to add fuses whenever I make any electrical changes. The 67 has original wiring and (cross my fingers) it is all in great shape. Have not found any significantly brittle wires. I did clean all the connections when I went through the car back in 2005.
Bruce Cunha

You want to leave the original wiring in place and basically use it to switch the relays on and off with their additional wiring to the lights with new connectors.

As has been suggested fusing is important but just relaying the headlamps will make them a good bit brighter I have measured say 15% to 20% without changing bulbs.

In the UK we can buy 100 watt bulbs but in that case use a relay per bulb not one relay as you would between two 55 watt bulbs.

Unless you have professional crimping gear and that is expensive, I would buy a made up set of wires. As you will have to source relay sockets and the special crimps for those all for just one job.

You want it to look neat. Also if the relays are in the bonnet look for some weather protection for them.

eddie
Eddie Cairns

Hi Bruce,

If you look under the slam panel you will see a bunch of connectors for the lights.
I installed my relays in this area and used the existing wires to actuate them. You will need to run a heavy cable(s) to feed power to the contacts.
There is some concern about water getting into the relays in this position, but in three years I've had no problems.

Herb
Herb Adler

"There is some concern about water getting into the relays in this position, but in three years I've had no problems."

Neither have I after mounting the relays in the same position and we live in the Puget Sound region of Washington State (Rain festival is celebrated ever year from Jan 1 through Dec 31). Cheers - Dave
David DuBois

Having just rewired and added relays and extra fuse to a 72 GT , I now have:-
Uprated headlamps
Two 60s very powerful spots
HRW that works effeicently and quickly (Fuse and relay)
Brake light switch now works a remote relay
Extra rear light for bad weather driving F&R
The last three are all in the boot and are spliced into the main loom and hidden away
At the front a new large power wire runs off a starter terminal to a new fuse block then to three relays in a block then to headlamps and spots
I also uprated all earth wires right from the headlamps and spots to body earth .
Total cost ( including the invaluable crimping tool )
£ 80-00
Last but not least recovering and covering loom alterations in loom tape is easy and makes the whole job look good but not concours
Get a colour wiring diagram and the double check the car - my PO was a buffoon.
It is easier to do with engine out !
And I now know a lot more about MG electrics then before
PS tell the insurance co !! these are Mods and if not declared can cause problems
ap lestocq

A slight case of overkill ?
The terminal lug to the right of the pix with the red cover has a direct lead to the battery via the starter solenoid using battery cable. This then feeds a bus bar located behind the fuse/relay which in turn feeds all the necessary relays & fuses with 12v
" The Devil finds work for idle hands"
Barrie E


B Egerton

Her's the wiring diag. for the headlights ,if anyones interested.Barrie E


B Egerton

I was bothered about water damaging the relays, after having one in a similar position on a Celica fail with corroded spaded. I chose to put them and the fuses behind the radiator diaphragm, the cost of a few extra inches of wire to reach the bullets by the right-hand headlight didn't seem worth not giving them that extra bit of protection. The two fused relays are for other circuits.


Paul Hunt

Basic principles are ; Use a relay to handle the switching of the main current; reduce the number of connectors; take the power feed to the relays from the starter motor or alternator (brown wire); fuses!
Look on Autosparks site for cable current ratings, relays and connectors, in-line fuses etc..
Allan Reeling

This thread was discussed between 05/06/2013 and 12/06/2013

MG MGB Technical index

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