Lucas 3aw relay

[Tom W]

This question relates to my e-type rather than the rover, but you lot are a knowledgable bunch so I thought I'd ask on here.

The Lucas 3aw relay that controls the ignition light has packed up. I could just buy a new one, but being inquisitive, I decided to dismantle it and see what was wrong. It seems quite simple inside, a coil of wire fed from the AL feed that heats up when sufficient voltage is applied, and opens up the terminals that normally connect the WL terminal to earth.

It looks quite fragile, and tempremental. It got me thinking, could I make an electronic version from something like this?

http://www.maplin.co.uk/p/lm317t-15a-3-terminal-adjustable-voltage-regulator-to220-style-case-uf27e

Problem is, I don't know anything about electronics. Any electronics wizards on here?

Cheers, Tom

 

[testrider]

My V8 is missing it'a 3AW relay and someone has substituted it with a normal 5 pin relay which seems to work.

 

[Dave3066]

There's an off-the-shelf electronic solution on the market already

http://www.holden.co.uk/displayproduct.asp?pCode=080.808

I have one fitted to my 3500S.

Dave

 

[Tom W]

For anyone interested, this is what's inside the 3aw



It doesn't look that complex

I was able to solder the broken spring back in place, but I've not got it calibrated properly yet. The light is off when the engine's not running and comes on when the alternator charges. I guess the points aren't making contact at rest and when the contact arm is moves, the wire touches on the back of the light feed before it reaches its stop. Easily fixed by bending the contact terminal.

I guess a normal relay will work. It just won't necessarily turn the light off at the predetermined voltage (about 7.5 volts). I don't know how critical it is that the AL lead from the alternator is connected to the same resistance as is provided by the 3aw.

I've seen the aftermarket solid state units before, I was just curious if I could make my own. For now, I've ordered a standard replacement which I'll fit, but I'll fiddle around with the original again to see if I can make it work properly.

Regards,
Tom

 

[Dave3066]

That's a great close up image, but it's MASSIVE :shock:

Can you make it a bit smaller please

Dave

 

[Tom W]

Hopefully this is a bit smaller, though it still looks large on my preview screen. I only have limited options on my phone and won't be back at my computer for a week or so.

Tom