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Re: Electrical puzzles '80 spit

To: ckigar <ckigar@sound.net>, spitfires <spitfires@autox.team.net>
Subject: Re: Electrical puzzles '80 spit
From: Richard B Gosling <Gosling_Richard_B@perkins.com>
Date: 20 Dec 2000 07:51:11 -0600
Chip,

Ooh, you have got a lot of fun with that car!  I hate electrical problems, and
 at least my car has almost all original wiring, apart from a couple of minor
 mods I made (cigar lighter wire used as live source for radio and clock,
 extension to light switch wiring to enable switch relocation, so clock could
 go where light switch was).  Wiring circuits should be reasonably logical, and
 you should be able to fix anything with a wiring diagram an patience, so any
 'bodges' introduced by the PO are almost bound to be bad repairs to fix a
 fundamantal problem that, in all likelihood, still remains as no-one has ever
 tried to fix it properly.

>From the start -

Your lift indicator flashing while the dashlight stays on is very bizarre.  One
 relay controls all the indicators - there should be a live to the relay, then
 the other side of the relay goes to the switch, which will connect to either
 the left or right lights, plus the dash light (this is from memory, I don't
 have the diagram in front of me, so I MIGHT be wrong - check the diagram).
 BTW, if you have the original drivers handbook from the car, the wiring
 diagram in there is easier to follow than the one in the Haynes Manual.  In
 any case, the supply to the switch is already on/off, so how a permanent live
 can reach the lamp I have no idea - you will just have to take the lamp and
 follow the wire lighting it, and see where it goes.

The left indicator not working when the headlights are on may be easier to
 solve.  My guess is that the indicator is not properly earthed, and somehow is
 earthing via the headlights (maybe through the side-lights and/or brake
 lights).  Thus, when the lights are on, the earth route is suddenly live, so
 there is nowhere for the electricity to go.  Check the continuity from the
 front and rear bulbs to earth, and clean up the connections.  You could
 install an extra earth wire connecting the lamp cluster casing to the car body
 just to be sure.

Earthing problems can cause all sorts of problems that are hard to track down.
 Often the symptom bears very little connection to the cause (e.g. poor
 indicators caused by inadequatley earthed brake lights).  You just have to
 check and clean all the connections.  A useful method is to go round checking
 everything vaguely related to the circuit you are testing with a voltmeter (or
 one of those screwdriver-looking things with a light in the handle that just
 tell you if something is live), you will often bump into a wire that is live
 when you would not expect it to be, or vice versa.

How the ignition light is connected should be clear from the wiring diagram.
 Off the top of my head, it should go between the live terminal of the ignition
 coil (or anything directly connected to that, including the ignition switch
 terminal, which would be easier), and the live terminal of the alternator.
 Thus, if the alternator is not generating anything, you have battery voltage
 one side, 0V on the other, bulb lights.  When the alternator is charging you
 have full voltage both sides of the lamp, so no voltage drop across the bulb,
 so bulb stays off.

I cannot see what the oil pressure warning light would have to do with the
 anti-run-on valve, or why they should be connected in any way.  I cannot check
 right now on a wiring diagram, but I would expect that a live would feed to
 the bulb, which would then be connected to the switch.  With no oil pressure,
 the switch would close the connection to earth (via cylinder block), bulb
 would light, with oil pressure the switch opens and the bulb does not light.
 I repeat, this would be my expectation, without ever having got involved with
 this circuit or looked at the diagram myself!

Are you saying that your switch has a total of 3 connectors on it?  Aah, I've
 had a thought about the anti-run-on valve - this may be an automatic cut-off
 device to protect you from your own incompetance - if the oil pressure drops,
 the anti-run-on valve would be activated, and that would kill the engine
 before any damage is done.  The anti-run-on valve would probably just be a
 valve in the inlet manifold which would open to allow extra air in, to prevent
 the car running by weakening the mixture.  This would normally operate when
 the engine is switched off to prevent that diesel-sounding rattley running
 that can continue for a few seconds after the ignition  is off, particularly
 in a hot engine, or one with a lot of carbon build-up in the head.  If you
 don't have a valve, don't connect the connector, everthing else will still run
 fine.

As you might have gathered I am not a total expert in the field, but no-one
 else has replied yet, so I thought you might appreciate the benefit of my
 limited experience!

Richard and Daffy (electrical gremlins were eventually tamed after 3 months of
 ownership, all fine since, touch wood(en dashboard))

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