I've got a 72 MGB/GT. My guess is that your 74 should be VERY
similar. My guess is that yes, you will have the same problem.
(I also put in a XR700 Crane.) So, part of your installation will
require you to fix your tach. There were a couple of thumb
screws on the back which you remove first, then remove the brackets
which these screws are holding. The tach should pull out through
the front of the dash. Pull off the wires (make a diagram to be
sure you get it back together right.) There should be two white
wires, one with a male connector, one with a female connector, and
a spade connector with two green wires. Also, there is a dash light,
and under one of the thumb screws should be a couple of ground
After you get the tach out, there are two screws on the back which
come out. The glass plate should come out by rotating the chrome
facia. Then, the innards should come out. Be _very_ careful at this
stage, since there are lots of delicate parts inside.
Next, slide out one of the connectors that the white wire is connected
to, and cut the white wire. (Be sure not to cut it too close to the
connector, since you will have to re-connect it.) Un-wrap the white
wire from the Current Sensing Ring (a bead of ferrrite? with lots of
little fine red wires wrapped around it that the white wire passes through.
Three times in my case.) Leave the white wire passing through once. Re-
connect the white wire where you cut it. (I used a crimp-connector for this.
You could also solder/shrink tube it...) Be sure to check that all that
extra white wire doesn't interfere with the tach mechanism. Put it
all back together.
Lastly, I hooked up an external tach, and adjusted the internal one untill
they matched. I made sure they matched at 1000, 2000, 3000, and 4000 RPM.
If you have any questions about the XR700 installation, let me know!
Hope this helps..
> On Fri, 30 Jun 1995, David Hall wrote:
> > Hello All...
> > Well, I went ahead and tried removing 2 loops through the current
> > sensing ring. This leaves the wire passing through the loop just
> > once. Works like a charm! I had to adjust the tach a bit using
> > its adjusment screw (actually, a potentiometer) to get it to
> > match up with my external tach, and now it works wonderfully!
> Dave, I erased the earlier part where you said what vehicle this was
> for. Please tell. I am about to put the Crane XR-700 EI in my 74 B, and
> was wondering if I will have the same problem of a jumpy tach.
> Eric L. Van Iderstine - ME - Mississippi State University
> elv1@Ra.MsState.Edu http://www2.msstate.edu/~elv1
> 74 MGB & 85 Buick (until I finish the MG)
> "An object at rest cannot be stopped." The evil midnight bomber
> what bombs at midnight FROM "THE TICK"