light stays on
Adrian Brook (Woodcote 1823) from East Yorkshire posted a note on
the V8BB about a difficulty he had with his no charge light and a
few weeks later reported the solution. (Aug
posting on the V8BB was "I have been on a long run today and
on putting the car away the no charge light has decided to come on
when I switch the ignition off and remove the key. I looked at wiring
diagram the light appears` to be connected` to fuse 3 with tacho,
air con etc. All of these are switched off as normal. I presume the
power source must be a short coming from the battery, through the
alternator or alternator sensor and back to the light I have removed
the bulb for the time being. Anybody had a similar problem."
few weeks later he posted a note saying "Found the problem. It
turned out to be a failed rectifier fitted in the alternator. The
battery was draining through the alternator and powering the no charge
light when the ignition was switched off." So how did he make
the checks to determine the rectifier had failed? Well here he explains.
I returned to the car next day the battery had drained completely.
It was suggested that it might be the alternator diodes so I checked
these using a multimeter and they were fine. If the diodes are defective
and shorted by excessive voltage they can be tested without the engine
running by setting the meter to diode function and removing the connecting
wires from the alternator. Put one probe to the casing and one to
the main output terminal. Note the reading, then reverse the probes
note the reading again. One way it should read 0.80V and the other
should over range OL or read 1.
then tested the built in rectifier by turning the meter to milliammeter
connected the probes in series between the output terminal and the
alternator output cable.
"Using your meter", a handy book available from Radio
Shack. It has a useful section on automotive testing. Diagram
leakage current should be less than 1mA - if it's higher it is probably
faulty. Mine had a high reading so I took the alternator to a local
specialist that reconditions and supplies alternators and starter
motors to the trade and public called Sissons Garage on Burma Drive
in Hull. They confirmed my diagnosis and supplied me with a reconditioned
one of the same manufacture, off the shelf for £41.
What multimeter do you need?
Adrian feels any multimeter will do these tests and www.cpc.co.uk
have some digital ones with a diode tester for around £4.50.