Witness Posted March 31, 2015 Report Share Posted March 31, 2015 (edited) Hi again I have a strange problem with my 1973 TR6. The red ignition light stays on when the engine is off and keys are out, when the engine's running the light goes out. Similarly when the alternator white connector block is removed the ligh goes out which points me to an altenator fault. Wwhy would the light stay on when the car engine is off? Does this indicate a voltage difference between the battery and altenator, with there baing a ground/fault at the altenator? If necessary I can get some pics of the altenator tonight and confirm make/model. Any advice/halp would be appreciated? Thanks Rob Edited March 31, 2015 by Witness Quote Link to post Share on other sites
peejay4A Posted March 31, 2015 Report Share Posted March 31, 2015 That's weird. One side of the bulb goes to the alternator output, the other should get a switched 12v feed from the ignition switch. I wonder if the switch has gone faulty. Quote Link to post Share on other sites
alec Posted March 31, 2015 Report Share Posted March 31, 2015 This happened to me last year 74 TR6. Thought it could not be the alternator as it was newish, checked my records 7 years old still should have been Ok. Fitted a replacement Lucas alternator from a local supplier. Problem fixed. I put the fault down to a faulty diode & again down to high under bonnet heat. Quote Link to post Share on other sites
Witness Posted March 31, 2015 Author Report Share Posted March 31, 2015 (edited) Thanks for the comments. Not being overly familiar with the electrics both seem reasonable causes for the fault. Pardon my ignorance but can the diode plate be accessed and fixed? Eg new diode, solder a broken connection or is it best off just getting a new altenator? Also how does a faulty diode effect the functionality of the altenator if I wish to run the car for a few days prior to fixing the problem? Thanks Edited March 31, 2015 by Witness Quote Link to post Share on other sites
Lebro Posted March 31, 2015 Report Share Posted March 31, 2015 (edited) Sounds like a diode gone short in the main rectifier pack. Yes you can replace the pack, but you do need a good (50W) soldering iron, & you need to 1) be reasonably proficient at soldering electronic connections, & 2) Not get the diodes too hot while doing it. Bob. Edited March 31, 2015 by Lebro Quote Link to post Share on other sites
alec Posted March 31, 2015 Report Share Posted March 31, 2015 Yes believe you can purchase a repair kit for the alternator. But a replacement alternator can be purchased for about £50 as an exchange. This ensures you should not have any further problems with bearings etc. If the alternator is quite new then a repair kit will be lot cheaper as long as you fit it yourself. I have had my TR6 30 rears plus & I think this is the 3rd alternator. Car has been unused for a number of years which does not help the electrics. But the last 7 years have covered 45k miles touring Europe Scotland Wales etc The reason the ignition light stays on can only be a diode allowing current / voltage back up to the ignition light. A auto electrician should be able to give you answers. Quote Link to post Share on other sites
RogerH Posted March 31, 2015 Report Share Posted March 31, 2015 (edited) Hi Rob, Hmmmm Roger PS - having read Bob's post and had a look at a diagram it isn't as I had understood. Edited March 31, 2015 by RogerH Quote Link to post Share on other sites
peejay4A Posted March 31, 2015 Report Share Posted March 31, 2015 Exactly. Where are the volts coming from with ignition off? Quote Link to post Share on other sites
Lebro Posted March 31, 2015 Report Share Posted March 31, 2015 (edited) The alternator is permanently connected to the battery via it's main diode pack. Normally the main diodes will block any flow of current from the battery into the alternator internals, but if just one of these diodes (6 in total) breaks down, then there is now a path from battery to alternator windings, & then via the smaller diodes to the IGN warning light, through that, & then through the coil to ground via closed contact breakers, or any other circuit which is ignition controlled, & may have been left switched on e.g. heater fan etc. Bob. Edited April 1, 2015 by Lebro Quote Link to post Share on other sites
peejay4A Posted March 31, 2015 Report Share Posted March 31, 2015 That I can understand and should be easy enough to check. Quote Link to post Share on other sites
Witness Posted April 1, 2015 Author Report Share Posted April 1, 2015 Great info thanks folks, so the red light is doing its job. I'll get the voltmeter out at the weekend and no doubt be getting a new alternator ordered up ASAP, I'll let you know the outcome. Quote Link to post Share on other sites
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