The ignition warning light acts as the 'primer' for the alternator to start
charging. If that light is not working the alt is almost certainly not
being primed properly, and although they are usually self-exciting once the
engine is revved to about 2000 rpm it is possible that the battery is not
being properly charged. Oh, and it should light when you first turn the
ignition on, i.e. before the turn the key to 'Start'.
Watching a light e.g. interior light when you turn the key to 'Start' will
tell you if the battery is flat or if you have bad connections in the heavy
current circuit, but only a voltmeter on the battery posts (not the
connectors) will tell you which. However a broken engine or transmission
ground strap will affect cranking without dimming the lights. If it is
battery or connections there is usually enough power to elicit a 'clonk'
from the solenoid/starter, or possibly a chattering solenoid, unless the
battery is very flat/connections are very bad in which case you wouldn't get
bright headlights.
Given the above it is probabably a failure in the start circuitry - the
ignition key puts out 12v on a white/red which operates the starter relay,
which puts out 12v on a white/brown to operate the solenoid. The relay
operates with a click, and the solenoid with a much louder click. The relay
is usually high up on the RHS inner wing near the fuse-block.
PaulH.
----- Original Message -----
From: John Middlesworth <middlesworth@worldnet.att.net>
To: <mgs@autox.team.net>
Sent: Wednesday, July 18, 2001 1:12 AM
Subject: Problem with starter motor?
> I need help analyzing a problem. My 72 MGB suddenly refuses to start. I
> can hear the fuel pump working and (perhaps) a single click from the
starter
> solenoid, but not a bit of movement of the flywheel. Here are the
relevant
> facts:
> 1. The headlights are bright enough to indicate a good charge on the
> battery.
> 2. The red ignition light on the dash which normally lights up when the
car
> is starting never lights.
> 3. In attempting to remove the starter motor I accidently hit a live wire
> (battery not properly disconnected) and heard the starter gear whirl
around,
> so the motor's not entirely dead.
>
> Does it sound like I need a new motor, or perhaps a new solenoid, or
should
> I check something else?
>
> John Middlesworth
>
>
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