|
Author
|
Topic: Tachometer Question
|
jay67fast
Gearhead Posts: 146
From: Boca Raton, Florida,U.S.A.
Registered: Nov 2004
|
posted 05-24-2006 12:57 PM
 
I could use some help with a problem that popped up. When my 67fastback was restored by the PO, it went from a standard interior to a deluxe SS interior. One of the changes made was the standard instrument panel was replaced with the deluxe panel, which included a tach in place of the oil pressure and temp gauges.
O.K. Fast forward to last Sunday. I’m driving home from a car show and the car dies as I’m driving. After playing around on the side of the road I realized there was no spark to the coil. Rather than waste time, I disconnected the coil wire and hot wired from the positive terminal on the solenoid to the coil. The car started fine and I got home with no trouble. Monday, when I checked, I found that the problem was the wire from the ignition switch to the coil. Rather than try to find out where the wire was corroded, broken, or God knows what, I simply cut the resistance wire at the ignition switch connector and ran a new wire to the coil. The car runs fine except the tach doesn’t work. Since it worked fine before this problem, I believe that when the PO installed the new instrument. panel he powered the tach by splicing into the same wire that I had to change. I tried to see what he did under the dash, but I guess over the years some “creative” wiring repairs were done, and the result is it’s impossible for me to trace the tach leads. I checked in the manual, and it has nothing about the tach anywhere in the text, or in the schematics. I’m lost—I have no idea how the tach works or what to do to get the tach working. If necessary I could clip the tach leads and run new wire to power the tach, but I don’t know where to hook them up. It appears the tach has two wires coming out of the back. Is this correct? What’s confusing the issue even more is that the wire I replaced included the resistance wire. Since I’m running a Pertronix unit, I eliminated the resistance wire and ran the new wire with full 12 volts to the coil. I’m not sure if the tach is supposed to be powered by a 12 volt source or a 6 volt source. I think t it was hooked up to the wire after the resistance wire, since I know there was no other wire spliced into the resistance wire.
Can anyone out there explain how the tach gets it’s power, and how it gets the impulse needed to register on the gauge. Also, can anyone tell me how to hook up the tach if I clipped the wires at the back of the tach and started again?
I’d appreciate any help you could give me.
Thanks,
jay67fast
|
Scott H
Gearhead Posts: 1480
From: Chicago area
Registered: Mar 2005
|
posted 05-24-2006 10:17 PM
Ford factory tach is supposed to work in series to the coil.Power comes from the ignition switch, goes into one side of the tach, comes out the other side of the tach, and then straight to the coil. Hope this helps!
|
sigtauenus
Gearhead Posts: 3969
From: Va Beach
Registered: Jun 2000
|
posted 05-25-2006 08:03 AM
I've had the exact same experience you have had except my 68 has a factory tach. The wire you cut out, the pink resistance wire, fails over time. Additionally, that same wire is run in series from the ignition switch to the coil, just as Scott said.
| |
