[Mgs] 1972 MG Midget wiring question

[Paul Hunt]

Whilst the panel lamps and wipers not working could be due to a common 
ground fault, there is no connection between that ground and the turn 
signals.  Neither would removing the heater have any effect on any other 
circuit, *unless* the 12v wire were allowed to come into contact with a 
ground while the heater switch was on (which should blow the fuse).  But if 
the wires weren't connected to the switch either then there is no way they 
can affect anything, unless the *green* wire at the switch came into contact 
with ground (same result as before).

If the rear lights aren't working either then you need to be looking at the 
12v feed to them, not the grounds which are all independent.  Have you 
looked for 12v on any of the wires yet?  You should, with a meter or 
test-lamp (i.e. a bulb with a couple of wires soldered on if nothing else), 
you will never diagnose electrical problems without that.  I still haven't 
been able to locate a 72 Midget wiring diagram on the web but a 72 MGB has a 
4-fuse fusebox and the top two fuses are for the parking lights, one fuse 
per side.  There is a single red/green going to the front of those two fuses 
(they are linked together underneath).  The back of the top two fuses has 4 
red wires, 2 per fuse, and these go out to the corners of the car.

With the main lighting switch in its middle position (parking lights only) 
see if you have 12v on the red/green.  If so, check the other side of the 
fuses.  If not check at the main lighting switch itself, and any connectors 
between it and the main harness.  If the parking lights aren't working *or* 
the panel lights, the switch or its connections are a common cause.

With the turn signals check you have 12v both sides of the flasher unit 
(it's not really a relay) with the ignition on, moving the turn switch on 
and off (both sides) to see if the voltage changes.  If it stays at 12v 
check the three connections between the turn switch and the harness.  If 
there is voltage on one terminal of the turn flasher but not the other the 
turn flasher is faulty.  If it's on neither terminal of the turn flasher 
check the two green wires (I'm assuming) on the hazard flasher.  On one but 
not the other, with the hazards off, means the switch is faulty.  On neither 
means the fused ignition supply isn't reaching it, could be a bad connection 
at the fusebox or one of the several green bullet connectors behind the dash 
pulled apart or corroded.  That's assuming that at least one of the other 
fused ignition circuits like brake lights, fuel gauge etc. are working.  If 
none of those are working then you need to check the green circuit fuse, but 
if there is no voltage on the white terminals of the fusebox then the 
ignition switch or its connections.

In fact if you have the main lighting switch on the steering column housing, 
the one common pint for all these problems is connections around the 
steering column.  Not that poking around there is any substitute for proper 
diagnosis, of course >:|

PaulH.

----- Original Message ----- 
> So, my panel lamps are not working and neither are the windshield and 
> signal
> switches...