In a message dated 5/15/99 3:51:23 PM Eastern Daylight Time,
mtgaines@cs1.presby.edu writes:
> First, as you point out, I had the ballast resistor
> wire mixed up with the seat belt wire. But I THINK the brown wire
> which connects to the coil along with the white/yellow one is actually
> the resistor wire. It is cloth wrapped and dirty but it does sort of
> resemble a shoelace and it has a pinkish sheen to it when wiped
> clean. It is no fatter than most of the wires, and I was expecting a
> fat one for the ballast resistor.
Tim,
You're probably right. The ballast wire is not much bigger than the other
wires, but the insulation looks a little bit funky compared to the others.
>From your description of how it was wired, I think this is indeed the ballast
wire. (color codes are great, but sometimes the colors can change with age
and dirt, and really confuse the issue)
> So if I'm right (now) the ballast
> resistor wire and the white/yellow come together right at the coil.
> That would be okay, right?
Yes, the two wires usually come together very near the coil connections.
Connect both of them to the + post of the coil.
> The really interesting thing is that
> the PO put in a horn relay instead of a start relay. In other words
> there are two horn relays. From looking at parts catalogs, it appears
> that the start relay was indeed the same as the horn relay up through
> 1973. It costs about $40 dollars less than the correct start
> relay for my 1974! Anyway it has no C4 connector for the white/yellow
> wire.
Up till '74, the TR6 had no ballast resister, so the relays were the same, at
least functionally.
> Cheapskate that I am, I am wondering if it would be possible to make
> do with the horn relay as my start relay.
Yes, see below.
> My first thought was that
> it might be okay if the white/red wire to the solenoid and the white/
> yellow one to the coil are joined so that both carry voltage (connected
> to brown) when the relay is energized. Would it be bad for those two
> to be joined all the time when not carrying voltage?
YES! It would be VERY, VERY, bad! Three things would happen -- the car
wouldn't run, the starter solenoid would alway be trying to energize, and the
ballast resister would smoke! Connected that way, the reduced coil voltage
would always be applied to the solenoid anytime the ignition key is on
(remember, the w/y wire carries EITHER the full voltage OR the reduced
voltage, depending on the state of the relay). The resistance of the ballast
is so much higher than the solenoid that the solenoid wouldn't actually
engage, but it would draw current. Compared to the resistance of the ballast,
the resistance of the solenoid is so small that it would look almost like a
direct short to ground to the ballast resister.
Don't feel bad about thinking it up, as this is a very common type of error.
In any large industrial engineereing office, there is usually a small section
of engineers that do nothing else but look for these types of errors --
called "sneak circuits," as the power is "sneaking" somewhere other than
where you want it. Sneak circuits rarely occur in the initial design phase,
but when the circuits are modified later, it is VERY easy to create one.
> And one question about your instructions. The white/red wire from
> the ignition switch that should replace white/orange at the W1
> connection; that is not the same as the white/red normally connected
> to C1 is it? Because if it IS, then I think I can use the horn relay
> and still keep everything separated until the relay is activated.
They're not the same, but you can treat them as if they were. Connect both of
them to the W1 terminal. The only potential problem with this is the ignition
switch contact ratings. I would assume the switch ratings didn't change from
the earlier models, so it should be capable of handling the solenoid current.
If you want to be absolutely sure, we could add a $5.00 auto parts store
relay to go between (interpose between) the ignition switch and the relay,
and let the cheap relay handle the power. I don't think it is necessary, but
I can't guarantee it. If you want to use an interposing relay, let me know
and I'll write up the instructions for it. It's very easy to do.
Connect the white/yellow wire to one of the C contacts, and the brown wires
to the other C contact.
There is another possibility that is even cheaper -- look at your starter
solenoid and see if there is a smaller terminal that is not used. In some
applications, this terminal is used to bypass the ballast for starting rather
than using a relay. It is hot only when the solenoid is energized. If you
have this terminal, just connect the white/yellow wire to it. Some of the
Lucas solenoids are generic, and were used in multiple applications, some
using this terminal and some not. You just may be lucky enough to have one.
Just verify that the terminal has 12 volts when the solenoid is energized and
0 when it isn't.
In this case, the white/red wire FROM the ignition switch goes to the W1
terminal, and the white/red wire TO the solenoid goes to one of the C
contacts.
Dan Masters,
Alcoa, TN
'71 TR6---------3000mile/year driver, fully restored
'71 TR6---------undergoing full restoration and Ford 5.0 V8 insertion - see:
http://members.aol.com/danmas/
'74 MGBGT---3000mile/year driver, original condition - slated for a V8 soon
'68 MGBGT---organ donor for the '74
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