First give the glass a sharp rap with a knuckle when revving the engine,
sometime the pointer or movement gets sticky. If this suddenly gets it
working again the movement may need rebuilding or the instrument replaced.
An electronic tach needs a 12v and ground supply plus a signal. On a 74 the
12v should be a green wire which feeds a number of circuits via several
4-way bullet connectors, one of these may have pulled out. The ground comes
from a black wire which also feeds the instrument panel lighting. If this
fails the symptom is usually that the tach works with the lights off but not
with them on, if the panel lights work at all, that is.
The signal on a 74 *should* be a white/black from the coil negative
(changing from a white loop from ignition switch to coil for the 1973 model
Only when you have proved the problem isn't one of the above go delving into
the electronics of the tach, they are generally very reliable.
----- Original Message -----
Sent: Sunday, December 12, 2004 12:20 AM
Subject: Tach not working
> Hi Gang. The tach quit "taching" on my son's 1974 CBB. Where should I