In reply to a message from Tom96 sent Sun 8 Mar 2015:
did you get this resolved? I had a similar problem with my
84 XJ6, it ended up being a couple of things. a cooked
field wire, which killed my new replacement alternator.
wire replacement, and 2 alternators later it’s in good
order. this is how I figured it out.
with the car off, check the volts out of the battery.
should be around 13.3 to 14 DC, and amps are somewhere
around 30 to 40. I wear rubber mechanics glove for these
tests. the volts won’t kill you but the amps will. 500mili-
amps is all that is needed to stop your heart. BE CAREFUL!!
disconnect the positive post BE CAREFUL NOT TO GROUND
HOUR WRENCH ON THE HOOD LATCH, it will weld your wrench to
the car and seriously get your attention (better yet
disconnect the ground first). set your meter to Volts DC,
connect the positive meter lead on the bulkhead lead and
the negative meter lead on the positive post on the
battery. (reconnect the ground after the positive lead is
disconnected) fire up the car, check the voltage on the
meter, switch over to DC Amps and do the same check, it
should read somewhere around 13v and 25 - 40 amps.
if not, then on the drivers side (LHD point of view). next
to the brake booster there is another Battery/alternator
post. This post connects the two alternator (to the)
battery leads (brown wires) to the alternator, do the same
check there. the reading should be the same as the right
and left side of the car.
you can do the same test between the brown alternator wires
to the post. disconnect the alternator wire (brown) from
the left bulkhead posts, connect the meter between the
alternator wire (positive meter lead) and (negative meter
lead) to the post. fire up the car and check the voltage
(be sure the wires are reconnected on the right side to
avoid any sparks or shorts.
Do the same tests with the meter switched to DC Amps.
if any of these tests result in lower than 12 volts or 30
amps, check your wires for broken, cooked / discolored or
broken insulation, make sure the wire connected the clips
are is good order, Brakeclean works well for getting the
gunk off the wires. if the wires are in good order, then
check the field wire.
the field wire is a single brown wire running from the
alternator around the front of the engine (with the AC and
air pump wires) to a connection under the intake manifold.
the field wire drives the gauge in the car. make sure it’s
in good shape. This one is prone to getting cooked because
it runs along the block under the exhaust manifold along
the front of the head above the water pump, then between
down between the intake manifold and the block to a multi-
connector just behind the shock tower on the right side.
this is a hard one to test because it’s not real
accessible. with a bit of struggling, you can get to it
from under disconnect the belt tensioner and the belt,
force the alternator all the way to the left away from the
engine, and it’s just around the back on the right side of
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