The MGA With An Attitude
FUSE BLOCK - Which Fuse Goes Where? - ET-102A

At 02:53 PM UK time 5/30/03, Bob in Pittsburgh wrote:
"Where do the 35 amp and the 50 amp fuses go? Which is the A1-A2 etc???"

Lucas dual fuse block Notice that the MGA fuse block has five screw terminals. In original orientation the center terminal goes at the top. That terminal is electrically common with the next screw down on the left side, giving two output terminals for the top fuse. Power inputs are on the right and fused outputs are on the left (as you stand looking at the unit).

The bottom fuse position is for the horn only. This takes a 25/50 fuse, Brown wire on the right and Brown/Green wire on the left.

The top fuse position is for everything in the car which is fused and is switched on with the ignition switch. This takes a 17/35 fuse, has 3 White wires on the right and 4 Green wires on the left (2 per terminal). One white wire is power input from the ignition switch. The other two White wires are unfused power going to the ignition coil and fuel pump. The Green wires go to the wiper motor #2 terminal, fuel gauge "B" terminal, flasher unit "B" terminal, and the brake light switch.
Lucas dual fuse block
Additional foot note: The screw threads for the terminal screws in the fuse box and voltage regulator are 1/4-26 BSF threads. If you need replacement screws I suggest you find a junk fuse block or junk regulator. The screws are obviously still made, somewhere in the world, as replacement regulators and fuse boxes are still being supplied. I just have no idea where to buy the screws new in the USA.
Lucas dual fuse block In the picture at right you can clearly see spaces to store spare fuses. But the bottom wires are wrong. Brown wire shoud be below white wires and the brown/green wire should be below the green wires. Also two spring clips to hold the spare fuses are missing in this picture.
Lucas dual fuse block
In picture at left, with the two working fuses removed you can clearly see the jumper at upper left connecting the two A4 terminals, and the center spring clip that holds the two spare fuses.

There are a few tricks available with this fuse arrangement. You can pull out the bottom fuse and inset one end of it between the brown wire and white wire clips. This will connect battery power to the top fuse, same as turning on the ignition switch. You can then pull the starter switch to start the car from under the bonnet without the ignition key.

You can pull out the top fuse and inset one end of it between the brown/green wire and green wire clips. This will connect battery power to green wires without connecting the white wires. You can then do diagnistic work on fuel gauge, turn signals, brake lamps, and screen wipers without energizing fuel pump or ignition coil. Note that this will connect the excess value lower fuse to the green wire circuits. If you want to do that, you can put the 17/35 fuse in the lower position, then use the other fuse to short the clips together for the green wire connection. Just don't blow the horn when in this configuration.

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