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Subject: O/D relay

To: spitfire list <spitfires@autox.team.net>
Subject: Subject: O/D relay
From: llst <llst@shaw.ca>
Date: Tue, 15 Apr 2003 19:19:43 -0700
Date: Mon, 14 Apr 2003 12:31:53 +0200
From: <Peter.Bona@vodafone.com>
Subject: O/D relay

The weekend I fried my D type overdrive relay. One of the points has
been badly burnt, so no chance to repair it. I found a local non LBC
supplier having relays, I think these are mostly horn or headlamp ones. 
My question is, that what differences are between 3 and 4 point relays?
In spits O/D has 4, horn has 3 points relays. As I have checked on the
diagram, the O/D relay is connected by two wires to the 12V, a brown and
a white one. It seems to me that the brown is constantly on 12V as the
white only with the ignition on. So why is it like this? Do I really
need a 4 point relay or 3 point is good as well? And what about the
current? 20A should be enough or it is better to have more.

thanks for ideas,
peter

ps: 68' mk3 


Peter, many years ago (20 +) I tried to use a horn relay for an od relay on a 
TR3A and I found that after several continuous hours of running, the relay 
would burn out. It would last for several weeks but eventually give up. I 
believe that there is a difference in that the od relay is meant to be a 
maintained relay and the horn relay is just a momentary type relay and as a 
result it may not last. You never know though, relays now a days may be 
different or just a different manufacture may make one that lasts. It's worth a 
try if you go down to the wreckers and pick up a few for a few dollars. If your 
buying a new one, see if they have a maintained one, maybe one from an air 
conditioning circuit might do the trick.

Larry Ternowski
Langley BC

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