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Re: Wiring

To: brucemills@dccnet.com, mgb-v8@autox.team.net
Subject: Re: Wiring
From: DANMAS@aol.com
Date: Mon, 12 Mar 2001 21:53:53 EST
Reply-to: DANMAS@aol.com
Sender: owner-mgb-v8@autox.team.net
In a message dated 3/11/2001 11:38:14 PM Eastern Standard Time, 
brucemills@dccnet.com writes:


> I am installing a coil/fuel pump shut off in my 74 = MGB. I know that the
> white wire coming from the ignition into the engine bay is the one I am
> after, to cut and install the shut off for the coil/pump.
> I have opened the harness just behind the glove box which then runs into the
> engine bay. In the harness are 2 white wires, one is a thicker gauge white
> wire, identical to the one which comes from the ignition. The other is a
> lighter gauge white wire. When I do a continuity test between the ignition
> and either the lighter gauge or the bigger gauge wire I do get continuity on
> both of them. I know the bigger gauge white wire goes to the fuse and there
> joins with a lighter gauge white wire goes to the fuel pump. I have traced
> the white larger gauge white as much as I can (and disconnected all plugs
> except the ignition plug, still getting  continuity on the lighter gauge
> wire) so what is this lighter gauge white wire for?
> While I was digging around under the dash on the back of the metal brace
> where the radio goes through is a black box. This wouldn't be the inertia
> switch would it? I have owned this car for 15 years and thought I knew every
> 

Bruce,

The lighter white wire should be for the alternator (ignition) warning light, 
and the heavier white wire should be for the fuel pump/coil. And, acccording 
to my diagrams, the smaller white wire also feeds the WS washer pump, which 
doesn't comply with normal Lucas color codes.

I usually advise folks not to use continuity tests unless you REALLY know 
what you are doing, as the results can be VERY misleading and confusing! When 
I say "know what you are doing," I mean know EXACTLY where the wires go, and 
what wires are connected together.

What color are the wires on the "black box" you found? I don't believe the 
inertia switch appeared until later models, but who knows? If it's the 
inertia switch, they should be white, and perhaps white/brown.

May I make a recomendation? When you wire your cutoff switch, use a SPDT 
switch, and wire the normally closed contact to a warning buzzer. That way, 
if you forget and try to start the car without turning on the pump/coil, the 
buzzer will sound to remind you. I have one on the fuel pump in my TR6, and I 
hear that buzzer quite often, as I often forget to turn the switch on. 
Sitting there grinding away on the starter because you forgot can be 
embarrasing (or, in my case, running out of fuel about a block down the 
street after the float bowls are emptied)!

btw, you missed a great V8 get-together last week.

Dan

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