This week I replaced the alternator on my 1978 MGB roadster. I had suffered
an electrical meltdown that burned the wiring from about 6" away down to and
through the connector that goes onto the back of the alternator to attach the
wiring. After seemingly completing the job and having bolted and wired
everything back together, I went to start the car. I noticed that the panel
light that
says "IGNITION" on the dash in between the two big gauges (the Tach & the
Speedo) stayed lit no matter if the ignition was on or not. A first I thought
that
it stayed on due to a short caused by two wires that had melted together when
the alternator went ka-blew-ie!! (technical terminology, heh, heh!) I then
carefully undid the loom up to where the wiring showed no signs of heat damage
and spliced new wiring in to replace all damaged wires. Still no change, the
darn light stayed on growing fainter when the engine was running. Hoping that I
hadn't suffered a short elsewhere I backtracked the whole days progress,
rummaging through the burned and melted wiring that I'd cut & replaced with new
undamaged wires of the same gauge and size, I noticed what at first I'd
mistaken
to be a partially burnt wire and sheathing. Looking closer revealed it to be a
small diode that was spliced into the alternator "tickler" lead wire. It was
a suppresser diode that must act like a one way gate or valve. Remember
electricity flows in one direction like water in a tube. Evidently this diode
kept
the current from going up and making the IGNITION light stay lit. Once I'd
spliced it into the ticker wire the IGNITION light only went on when the
ignition
key was turned on and the engine was started, once the engine started the
light went off and it only reappeared if the motor went dead and thankfully it
immediately went off when I turned the key off. Only to reappear when the
ignition was switched back on, as it should. But I've never seen this type
diode
before on any alternator other than one on my PEUGEOT diesel. Is it a normal
thing
to have this suppressor diode on the alternator "tickler" wire? It's a new
one on me...
-=Safety-Fast=-
Albert Escalante, owner-1978 MGB
Central Coast British Car Club (Ca.)
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