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The joys of Lucas electrics  Rate Topic 
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 Posted: 04-08-2017 09:51 am
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chrisl
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I have had a problem with a short circuit in my GT that doesn't affect its running or driving but prevents the interior lights coming on or the clock working. Have fixed it once, but it promptly shorted again.

I forgot about it (another one of a million small jobs to do) until this afternoon when I was looking at the wood trim panels in the GT as they need refurbishing. To get a feel for how much work is involved with taking out all the knobs in the centre panel, I gave the 'panel' knob a slight tweak. Lo and behold the clock started working again, the interior lights came on... Even the light in the back that comes on when you open the rear hatch now works.

Obviously the problem is till there somewhere; but the Prince of Darkness walks a strange path...

(It's not true that Lucas, in 1947, tried to get Parliament to repeal Ohm's Law. They withdrew their efforts when they met too much resistance).

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 Posted: 04-08-2017 01:26 pm
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Brett Gibson JH5 20497
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I did a bit of wire sorting on a couple of GT's and the biggest culprit I found was the fuse block in the engine bay, those riveted connections become sloppy, I ended up removing the block, then used a center punch and hammer to "whack" the rivet to get it to tighten up, solved a lot of issue's. Of course that doesn't fix lose connections behind the dash, just the main power line.
Brett

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 Posted: 04-09-2017 05:52 am
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Esprit2
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chrisl wrote:
(It's not true that Lucas, in 1947, tried to get Parliament to repeal Ohm's Law. They withdrew their efforts when they met too much resistance).Lucas doesn't claim patent rights to darkness. Only sudden, un-expected darkness.

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 Posted: 04-09-2017 10:00 am
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NigelK
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Hi Chris

I've had ongoing issues with my interior lights. The Prince of Darkness is temporarily in hiding, but he'll definitely be back. The interior lights and clock are on the same fuse, so presumably that was the first thing you checked. If the lights keep shorting out, firstly check that the body of the interior light delay relay is not touching its mounting bracket, which is on the panel by your right knee when you're in the driving seat, just under the bonnet release handle. Sometimes you just need to twist the relay cylinder just a little, so it is not earthing on the bracket. If that's OK, then check the wiring of the map light in the passenger door. According to the wiring diagram on the JOC website, operation of this light is entirely unrelated to the opening of the doors, but on my GT a PO had wired it into the delay circuit, and it kept blowing the fuse. Maybe three lights all on the same fuse was too much? Anyway, something else to check.

I have no idea why giving the panel knob a "tweak" might make the clock and interior lights work again, other than to suggest that the wiring for all the rear lights should be running under the bottom of the central wooden panel back along the side of the transmission tunnel, and maybe you disturbed something there. Once you've got the wooden panel off, you'll be able to see if there are any errant chocolate block connectors in there.

By the way, removing that wooden panel is a pig of a job. The choke and panel knobs should have allen / grub screws in the side allowing the knobs to be pulled off. They wouldn't budge on mine, and I did not want to break either knob by forcing the issue. Then you need to disconnect the heater controls - this is easiest to do by unfastening the cables from the sides of the heater box, don't ask me how I know. In the end I managed to pull the wooden panel far enough out so I could remove the radio for refurbishment, but I've never sworn so much in my life.

Best wishes,
Nigel

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 Posted: 04-09-2017 11:12 am
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chrisl
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Indeed the electrics are a frustrating mystery in this thing. The interior lights worked when I got the car; I switched them to 'off' so I didn't flatten the battery while working on it a couple of years ago and shorted them out. Got them going only for it to happen again - and now they are working perfectly after the 'panel' switch tweak (the clock is also keeping perfect time).

Go figure... To be honest as long as it starts and the brake lights work, I'm happy.

I am not looking forward to taking the dash apart. I have previously taken out all the other panels panels but not the centre piece with all the small instruments on it... Your tips appreciated.

I'll do some maintenance on the electrical connections at the same time although no doubt all the disturbance will stuff something up.

The original wood is de-laminating and looks a bit ordinary. I'm a reasonably competent woodworker so might make a new set of panels out of local jarrah (red/brown hardwood) or marri (much lighter); winter is coming and it's the time of the year when I can get lots done, too hot in summer.

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 Posted: 04-10-2017 07:08 am
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Frank Schwartz
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One of the biggest problems with the dash lights is the rotten Lucas dimmer switch. If you ever have to open a defunct one, you will see why...multiple fingers working on a ridiculous looking pc board. I replace it with a true rheostat switch from an older XJ series Jaguar, when I can find them in the junk yards...also I purchase new very bright bulbs from Delta for the instruments and you actually can see them at night...in truth, I'd just bypass the dimmer switch anyway..and all will be well...providing you use the newer bright bulbs..

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