Mallory Ignition Mallory TACHOMETER/FUEL INJECTION ADAPTER 29074_29078_49365 - Manual

1
TECHNICAL BULLETIN
TACHOMETER/FUEL INJECTION
ADAPTER APPLICATIONS
Since there seems to be some confusion and
misinformation about the applications of the Mallory
29074 and 29078 Tach/FI Adapters, we’ve put
together a little tutorial that explains why and when
each version is needed.
Background:
Years ago, before electronic ignitions were common
(and even after they were, in some cases), tachometer
designs were geared toward the existing point-type
ignition systems. This meant that a parallel-connection
tach (one that was triggered from the coil ‘-‘ terminal)
usually required a relatively high voltage (50-100v) to
trigger properly. The other type of tach commonly
used was the “series” tach, which was triggered by
the current pulse in the ignition supply line whenever
the points closed.
When aftermarket electronic ignitions started
becoming more popular, there arose a need for some
way to trigger these tachometers, most of which were
OEM designs. In addition, more cars were using
electronic fuel injection systems, and many of these
systems required a HV pulse on the coil ‘-‘ terminal to
tell them that the ignition was working before they
would trigger the injectors. The first “tach/FI” adapters
were just a coil of wire that simulated a weak coil
primary. Our version is the 29074. When connected
between the points trigger lead and the ignition power
wire, they would make a HV pulse on the trigger wire
when the ignition was triggered. In addition, they drew
a couple of amps through the ignition wire, and this
was generally enough to trigger a series tach that was
in the circuit.
As distributors with magnetic pickups became more
popular triggering sources, the 29074 style adapter
wouldn’t work, because the point lead was no longer
available as a trigger lead. In this case, a more
complex adapter was designed (the 29078). This unit
gets it’s trigger information from the “Tach” terminal of
the ignition box and generates a HV pulse for parallel
tachometers or FI systems, and it also pulls a couple
of amps on the ignition line to trigger series tachometers.
Application information:
Some of the problem with applications is because the
catalog description for the 29078 is incomplete. BOTH
adapters can be used for either tach (series or parallel)
or FI trigger. The issue that determines which is used
is the triggering method:
If you are using the points trigger lead (in other words,
points, OEM electronic, UniLite, 50-series, etc.) for the
ignition, then a 29074 is the appropriate adapter. It
should work with both parallel and series tachometers.
If you are using the mag pickup for triggering the
CD box OR if you plan to change from points/OEM
electronic/UniLite, etc. to mag pickup in the future,
the 29078 would be the choice. In this case, a parallel
tach or FI trigger would connect to the output of the
29078, rather than the CD box tach terminal.
FORM 1488M
9/04
Made in U.S.A.
Printed in U.S.A.
MALLORY IS A DIVISION OF THE MR. GASKET PERFORMANCE GROUP
10601 MEMPHIS AVE. #12, CLEVELAND, OH 44144
216.688.8300
FAX 216.688.8306
www.mrgasket.com