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MG MGA - Lindsay's extra fuse box

Hi,
A question for Lindsay please. I found the following in the archives (while searching for something else). It seems that I am behind the times in the electrical department. Is this still your latest thinking on how it should be done or have you made any changes to the layout? What about the fuses - 25A for fuse 1 then 35A, 25A and 15A ? have they proved to be OK?

I added two extra fuses to protect all the ignition components and the lighting a couple of weeks ago, quite a simple job and it seemed to work fine, but I did notice that with the headlights on, the lighting fuse did run slightly warm. I checked across the fuse with a meter and saw 0.01v drop, not a lot, but it got me thinking about the consequences of the fuse failing with fatigue and being plunged into total darkness; no lights at all! I felt I needed to do two things; relieve the pressure on that one lighting fuse and split the lighting circuits so that I don't lose both the head and the side lighting at the same time. So here is the re-worked fusing system just completed this morning. First of all, the extra two-fuse box I previously fitted is replaced with a Lucas 7FJ side entry 4-way fuse box. By a happy coincidence, the distance between the mounting holes on this fuse box exactly match the centres of the holes on one of the dashboard steady brackets, as you will see from the attached picture. So this is how I have wired it; the main power lead from the A1 terminal(brown/Blue) is disconnected from the ignition switch and connected to the feed side of the first fuse, the same side of that fuse (there is a double Lucar connector on both sides of each fuse) receives the wire from the ignition switch that goes to the common of the lighting switch, the other side of fuse one goes to the ignition switch via a new wire. The blue wire is disconnected from the lighting switch and is connected to the distribution side of fuse two, the red side/tail wire from the lighting switch goes to the distribution side of fuse three. A new blue and a new red wire are provided from the feed side of fuses two and three respectively to lighting switch terminals S1 and S2. The thick red foglamp wire is extended via a snap connector to the other distribution side lucar teminal of fuse three. The two red dash light wires are connected via a double snap connector to the distribution side of fuse four and finally the feed sides of fuses three and four are linked with a short piece of wire with a Lucar on each end.
So this is how the car wiring is protected: In the new fusebox, fuse No.1 (35A) supplies the ignition and fuel pump and the original fuse panel Ignition items; I have reduced this fuse to 25A so that it blows before its 35A supplier. Fuse No.2 (35A) supplies the headlamps. Fuse No.3 (25A or 35A if foglamps fitted) supplies the side and tail lamps and foglamps if fitted. Fuse No.4 (15A) supples the dashboard lamps and map light. Check out the picture to see where I have fitted the fusebox (cover removed).

Many thanks for your time,

Phil
p parmenter

I have been studying your thread Phil but you didnt appear to attach a picture as stated.

Lindsay must be away if he hasnt replied, no doubt he will be in touch.

Colyn
Colyn Firth

Hi Colyn,
Here is Lindsay's picture and a wiring diagram.

Phil

p parmenter

Diagram

p parmenter

Yes, I was away, just back from Spain today!
Phil, that was the basic fusing system I used. I have since modified it further by adding relays for the control of the headlights and ignition circuit to reduce the current through the ancient switches, thus extending their life. Using relays also increases the current through the headlamps by eliminating the voltage drop across the lighting switch and dipswitch contacts. The basic fusing system provides complete protection for all the circuits and will prevent an electrical fault from destroying your wiring loom or indeed the whole car! All that the standard two fuses protect is the horn circuit on one fuse and the wipers, stop lights, fuel gauge and direction indicators on the other. A short cicuit on the number plate light could burn out your wiring loom from the back of the car all the way to the lighting switch and beyond! I added fuses to protect 1)the ignition circuit (including everthing that is powered-up via the ignition switch), 2)the headlights, 3)the side and 4)tail lamps and the panel lamps. Because the circuits have separate fuses, a headlamp fault wont take out the side lamps as well, or a panel lamp fault (there is great scope for something to go wrong behind the panel!) will not result in the whole car being plunged into darkness. If you want details of how the wiring is now, let me know and I will draw you a diagram. Electrical safety is almost non-existant on British cars made before the 1980s and this lack can have nasty consequences.
Lindsay Sampford

Lindsay,
I'd be grateful if you could post the diagram with the relays added.
regards
Colin
C Manley

Many thanks Lindsay,
I think I'm OK with the wiring for the extra fusebox but as Colin said I'd be grateful for another diagram with the relays added.

Cheers,
Phil
p parmenter

I'd be similarly grateful for the updated diagram, Lindsay. I've been fearing a reiteration of the wiring melt-down I experienced with my first car, a 1958 Hillman Minx, after a minor short circuit.

Cheers,
Ken
Ken Korey

Adding headlamp relays is easy, just mount them near the end of the front part of the wiring loom where it splits to the right and left headlamps. Disconnect all the blue/white and blue/red wires and re-arrange as the attached diagram. This diagram and the one above tie-in with the standard 1500 wiring diagram. If you are using the 4 way fuse panel as above, change fuse #2 to 15A (or less if you like) as it only has to supply the relay current.
I can't remember how I wired the ignition relay as I did it on-the-fly and didn't draw a diagram, but although it simply involved the ignition switch operating a relay which switched a separate fused power supply to the ignition circuit, I seem to remember having to re-work white wires and also a problem with the ignition warning light holding the relay in after the the ignition had been turned off, causing the engine to continue to run. I sorted it out fairly easily but drawing a diagram that makes sense to others might present a problem.

Lindsay Sampford

This thread was discussed between 18/03/2012 and 20/03/2012

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