Here’s the weekly teaser. Put another way, help! I have a 1980 MGB that
suddenly started to exhibit the following problem: when the engine is
cranked over, the starter will not let go when the key is brought to the
“run” position--it keeps on cranking, even though the engine is now running.
The starter kept going even though the key was in the “off” position. By
flipping the key on and off, I was able to cut off the starter. In several
cases, however, I had to yank off the battery cover and shut off the battery
to shut off the starter. The problem did not occur all the time--the car
started normally on occasion.
1. My first thought was the solenoid: I pulled the starter and the
solenoid, inspected both, put everything back together again, and bench
tested the starter using jumpers--one to ground the starter the other for
positive voltage at the solenoid terminal. Then by running a clip line from
the + terminal of the battery to the ignition connection (where the
white/brown wire connects), I could activate the solenoid and get the starter
to work properly. When power was applied to the ignition switch connection,
the solenoid was thrown and the starter was activated for as long as I held
the clip line to the connection. When I removed the clip line, the starter
stopped, just like a good little starter should. I have not done this test
with the starter mounted on the car.
2. I replaced the starter, and also replaced the brake diode, which I
was
told, was the source of starter motor “run on.” That was the day before
yesterday. I’m not sure I quite understand the relationship between the
starter and the brake circuit other than the fact that there is a common take
off from the starter relay according to my wiring diagram. At any rate this
relay is apparently not there--the red and white wires (from the ignition
switch and the diode have been permanently joined to the white brown wire
that goes to the starter. I inherited the car this way, and it was not a
past problem. At any rate, the diode power comes off a fuse that should shut
down when the ignition goes off. (No other accessories--i.e. directionals
work with ignition off.)
3. Anyway, the car performed well for a day. Then today, the same
old/same
old. The starter would not cut out when the key was brought back to the
“run” position--or even when the key was off. To stop the starter I had to
disconnect the battery.
4. Any thoughts or advise would be appreciated.
John Trifari 1980 MGB
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