Chris,
The "loop" of white wire acts as the primary of a transformer. A change in
current through the loop induces a current in the secondary, which is the
metal piece on the back of the tach that the white wire wraps around. Every
time the points open or close, the change in current through the white wire
creates a current pulse the tach uses to measure the rpm of the engine.
As for continuity checking, some meters have an audible check that is very
convenient when it's hard to look at the meter and make the contacts at same
time. Good continuity for a 12V system should probably be a fraction of an
Ohm, which you will be hard pressed to distinguish from a few Ohms on most
meters. You can zero your meter by touching the meter probes together and
adjusting the meter needle to zero. But, I wouldn't take too seriously the
exact resistance you measure, just whether it is infinity (open) or close to
zero (continuity).
Hope this helps. But don't worry; just like Apollo 13, the guys at Mission
Control will work you through these difficulties. ;-)
Bob
-----Original Message-----
From: owner-tigers@autox.team.net [mailto:owner-tigers@autox.team.net]On
Behalf Of Chris Mottram
Sent: Tuesday, April 10, 2001 7:26 PM
To: tigers@autox.team.net
Subject: Tach Wire and continuity
Thanks all for the wiring harness fix replies. I
decided to pull it apart, check the wires and do a
continuity test. The only "melted" wire is appears to
be the one that runs through the loop behind the tach.
There is a plastic wire keeper that hold the white
wire in a loop. I need to replace this wire. I
assume the loop is needed to make the tach function?
(I dunno, the tach hasn't worked since I have owned
the car).
Dumb question #2 - In checking for continuity I use my
analog electric multi tester in ??? "ohms"?? mode?
And if the needle moves far I have good continuity and
if I moves only a tad or not at all I have bad
continuity?
Thanks,
Chris
PS What have I gotten myself into.....
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