Larry S., I can perhaps help some...
> ...(purple with orange wire). this is
> not shown on haynes manual wiring diagram.
While the Haynes manuals are good, they are oriented towards cars on the
eastern side of the Pond, thereby sometimes omitting a few details added for
the sake of us living a few thousand miles further west.
> i tested the brake system switch and it currently is zero ohms to ground
> is that what it is supposed to be ?
The brake indicator would be lit by the PDWA (Pressure Differential Warning
Actuator) to indicate when the dual brake lines had experienced seriously
uneven pressure. As a check that the bulb still worked and also that you
might have forgotten your handbrake (doh!), it also lit when the handbrake
was engaged. The handbrake switch is a simple to-ground switch under the
upholstery at the base of the handle. Hence the PDWA must be also, wired in
parallel with the handbrake switch. Thus too the wiring in the bulb socket
must have one wire that shows +12 when the ignition is on, and one wire that
shows ground when either your PDWA has been tripped or your handbrake is on.
Unfortunately the handbrake switch can become dislodged easily and shift
into either an always-on or always-off state. Fortunately, access to it is
moderately easy by removing the screws holding the armrest to the floor.
> ...what caused it to melt (sometime in the past) ?
Can't say. It depends on which wire is melted! The to-ground side could
melt if it touches a +12 wire while either the handbrake or PDWA switch were
closed. The +12 wire would melt if it touched anything grounded behind the
dash.
> i do not need the door switch going to light on dash
A "Door Ajar" warning? Are you sure that wasn't supposed to be an under-
dash courtesy light that came on when that side's door was opened? Of
course, the previous owner could have re-wired things.
> 2. anti-run on control valve does not appear to be working. car runs
> on. i believe it has to do with wiring.
(Didn't we go through this just a week or so ago?) If you have removed the
airpump and disengaged the EGR valve, then a reasonably-tuned engine with
good gas (it may need Sunoco Ultra or similar) shouldn't have a serious run-
on problem. Dieseling is usually a sign of plugs (or heaven forbid, valves)
running hot, or very dirty plugs or deposits in the cylinders still burning,
or poor gas. Check your timing carefully that it isn't too early. Check
your plugs and consider going to a colder plug if necessary. Of course, if
your compression is too high you may need higher octane gas than you can
find easily.
> one wire on the anti run on goes to pin6 brown/red on back of ignition
> switch (correct). other wire goes to rear
> terminal on oil pressure sender (toward firewall). i cannot
> make out any labeling on oil sender but there are three terminals.
> ...i can only describe physical position.
The physical position could vary depending on how the threads fit, so that
isn't worth worrying about. The three terminals should act like this:
One terminal closes to ground when you have no oil pressure. This one
should be connected to a wire that runs to the idiot light.
The other two terminals close to each other when you *do* have oil pressure,
and open when you don't. Unless it was mis-wired by the PO, one of these
should be that Ignition-Pin-6 wire, which should show +12 when the ignition
is *off*. The other should go to the anti-run-on valve. The idea was that
when you turned off the ignition, the anti-run-on (run-off?) valve was
engaged by Pin 6 voltage through the oil pressure sender. This happened
only while you still had oil pressure, so when the engine finally stopped
turning the switch would open and let the valve relax.
You can identify these three terminals by tracing their wires or watching
their voltage as you turn the ignition on and off. However if they were mis-
wired you should do this. Pull off all three wires, being careful that they
don't short against the engine! One of the terminals should show ground
with the engine *not* running, then show open-circuit (i.e. connected to
nothing) when the engine *is* running. This one is the activator for your
idiot light.
The other two should show zero ohms between each other when the engine *is*
running, and open-circuit (especially to each other) when the engine is
*not* running. Regardless of the engine, neither should go to ground but
you should check them anyway with the engine off. If either one does show
ground, first make sure that you haven't confused it with the idiot light
sender. Then when you do hook up the wires for the a-r-o valve, be
absolutely sure that the non-grounding one is the one that goes to Pin 6.
If you do wire up a grounding terminal to Pin 6 (and Pin 6 works properly)
you will get a short when you turn the key off. If neither of those two
terminals ever shows ground, then you can hook up the Pin 6 and a-r-o wires
to either terminal.
Now, getting the a-r-o valve to work electrically still won't help if the
vacuum line isn't functional. You'll have to use your ingenuity on that. I
haven't looked at mine in a while. The idea was that it applied vacuum to
someplace on the carb, possibly the float bowl, to prevent the jets from
getting any more fuel.
> 4. does anyone know how the brake failure warning light is supposed to
> be wired ?...(ugh, brake bleeding) ?
See above. Brake bleeding isn't difficult as long as the bleeder nipples
aren't frozen, and you'll want to make sure your brakes are in good shape
anyway. If your PDWA is tripped (or broken), you can always simply
disconnect it as a test that the wiring is functional. I would guess that
the PDWA is probalby okay, that it could be tripped and if so is resettable,
and that if it is broken the most likely case is that it simply won't turn
on at all. Of course, you'll never know that unless it actually gets
tripped by a brake-line failure.
> 4. should i connect a (larger) hose from the anti run on valve to the
> air canister ? or to the large hoses now on carbs / valve cover ?...
>is there a way to test the air canister and see if it is doing anything?
The cannister is simply a filter of sorts that is meant to absorb vapors. I
confess I don't recall how the hoses work. As I think about it, I would
guess that the vacuum applied to stop run-on probably can't go directly from
the manifold to the carb. So it may go through a cannister first... I'll
try to remember to check my Spitfire sometime soon. I'd suggest you work on
getting clean plugs and smooth running first. The a-r-o valve was a bandaid
over a problem that you'd rather not have in the first place.
Hope this helps.
Jim Muller
jimmuller@pop.rcn.com
'80 Spitfire (Percy)
'70 GT6+ (Nigel)
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