[6pack] TR6 Ignition Switch failures

[DAVID MASSEY]

 In what manner was it failing?  There are two main functions this switch does: 1) switch on the switched circuits to the ignition, wipers, heater, turn signals, brake lights and such (everything on the white and green circuits) and 2) to energize the starter solenoid.  Is it one of these that is failing?
The brown wire is totally unassociated with the ignition switch.  The lights work the same with the switch ON or OFF.  If it is passing too much current to the switch then that same amount of current will be passing through the blue wires and they should also be burnt.  If not I suspect a dirty/poor contact especially if the wire is burnt near the connector.
Another thing to check is the state of the wire harness.  If it is loose and rubbing against some of the sheet metal the abrasion could wear away the insulation and you may be getting intermittent short circuits to ground.  Everything may seem to work OK but the short term current spikes can cause incremental damage to the switch contacts over time.
The Red/White wire carries a significant level of current.  That wire is fairly large and they would not have used a large gauge wire if they didn't need it.  Later models (TR7's and TR8's) have a relay that is activated by the switch and the relay switches power to the starter solenoid.  But the TR6 ignition switch was designed to handle the current required by the starter solenoid and, indeed, the switches typically last a long time.
So, when you switch acts up what are the symptoms?
 
Dave 


 
 
-----Original Message-----
From: Jay Snavely <jaystr8 at comcast.net>
To: 6pack at autox.team.net
Sent: Thu, Jul 7, 2022 5:23 pm
Subject: [6pack] TR6 Ignition Switch failures

<!--#yiv4829406809 _filtered {} _filtered {}#yiv4829406809 #yiv4829406809 p.yiv4829406809MsoNormal, #yiv4829406809 li.yiv4829406809MsoNormal, #yiv4829406809 div.yiv4829406809MsoNormal {margin:0in;font-size:11.0pt;font-family:"Calibri", sans-serif;}#yiv4829406809 span.yiv4829406809EmailStyle17 {font-family:"Calibri", sans-serif;color:windowtext;}#yiv4829406809 .yiv4829406809MsoChpDefault {font-family:"Calibri", sans-serif;} _filtered {}#yiv4829406809 div.yiv4829406809WordSection1 {}-->I have just replaced the electrical switch part of the ignition switch on my 72 TR6, for the 2nd time in 2 years.  Both switches were genuine Lucas parts.  LU39415  The car has been driven a couple hundred miles during this period.  I am wondering if there might be a situation with the car that is causing the failures?  The wiring is pretty much stock, with a new harness 15 years ago.  I did add a voltmeter a few years ago, but retained the ammeter.  And added a circuit breaker in the headlight circuit. There was a burnt brown wire under the dash feeding power to the light switch, but I could not figure out if there was a problem or a dirty connector causing it to over heat.  Is there any reason to add a relay?  There doesn’t seem to be that much current in the red/white wire going to the starter solenoid.  Thanks._______________________________________________
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