On an MGB for that (69) year the tach needs a 12v supply for the electronics
and this comes from a green (fused ignition) wire and a black ground wire.
Often the tach will work without the black ground wire ... until you turn
the lights on. The signal for tach comes from a white wire from the
ignition switch on its way to the coil +ve. If the engine runs then this
wire must be continuous, but it may have been wired to bypass the tach
pick-up coil for some reason, or the tach itself is faulty, or the
aforementioned 12v supply is missing. Time to get the tach out and check
the voltages on the four wires. Take care with the whites, they are unfused
ignition. Grounding them will smoke the wiring.
The warning light also has one side connected to the white circuit at a
4-way bullet connector (four wires in it) by the ignition switch. Remove
the alternator plug, and with the ignition on ground the brown/yellow (NOT
the brown!) in the plug or connect a grounded test-lamp to it and this
should make the warning light glow. If so the alternator is at fault or the
plug wiring is wrong for the alternator. If not then either the bulb has
failed (I don't think I have ever known one of these fail) or a connection
in the brown/yellow or white is broken. The alternator, bulb holder, and
aforementioned 4-way bullet connector are the only connections shown.
PaulH.
----- Original Message -----
From: "James Schulte" <schultejim@msn.com>
To: <Mgs@Autox.Team.Net>; "MG Club Philadelphia"
<Philly_MG_Club@yahoogroups.com>
Sent: Wednesday, November 17, 2004 7:43 AM
Subject: Re: Tube shocks on MGC
> ... I just can't get the Tach and the ignition light to work.
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