Lotus Elan and Lotus Elan Plus 2 Forums

Moving onto the electrical system, have a couple questions that I was hoping to get some coaching on.

The control unit that came with the car has different lettering then the wiring diagram, if I connect them all in the same order left right are the internal connections all the same? in other words if the wiring from the 69 diagrams is faith we applied to the control box even if the letters on each terminal or not identical if I have the wiring to the right terminal from left to right or am I OK?

I’ve also seen some cases where people have ditched the control box all together and simply connected the wiring absent the control box, that might be a bit neater I suppose but it seems like it might make troubleshooting more difficult?

Given that I’m gonna try to start this thing soon I should probably have a working ignition switch. My ignition switch is present but the key is not, so I need to replace it, and I’m wondering if a similar vintage Mgb or triumph ignition switch can be substituted? I’m pretty sure I have some of those hanging around from prior cars but wanted to ask if anyone knew for sure.

Thanks!

Sorry I can't be helpful but I'm just getting into rewiring. What is the -control unit-?

Sometimes called a control unit and/control box. This is an MGB picture but looks the same and was widely used in that period among many British car makers.

USA64 wrote:Sorry I can't be helpful but I'm just getting into rewiring. What is the -control unit-?

Does your car have a dynamo or an alternator fitted?

tdskip wrote:

908DD406-24CA-49F0-9F0F-C5CAFFBDBF90.jpeg

Sometimes called a control unit and/control box. This is an MGB picture but looks the same and was widely used in that period among many British car makers.

USA64 wrote:Sorry I can't be helpful but I'm just getting into rewiring. What is the -control unit-?

In the UK it's normally referred to as a voltage regulator control box. RB340, usually used with the negative earth system & alternator. It's predecessor was an RB106/2 for the positive earth, dynamo cars.

tdskip wrote:My ignition switch is present but the key is not, so I need to replace it, and I’m wondering if a similar vintage Mgb or triumph ignition switch can be substituted? I’m pretty sure I have some of those hanging around from prior cars but wanted to ask if anyone knew for sure.

Yes.
The Lucas switch was widely used on many vehicles of the period so you may have a suitable replacement among your "stock" Some switches have 3 positions (off/run/start) while the Elan one has 4 (aux/off/run/start) but the lock barrels are the same and interchangeable as far as I know. New replacements of both switch and lock are widely available ... at least in the UK.

elans3 wrote:In the UK it's normally referred to as a voltage regulator control box. RB340, usually used with the negative earth system & alternator. It's predecessor was an RB106/2 for the positive earth, dynamo cars.

I don't think this is correct.

The picture posted by 'tdskip' is a Lucas 4TR, used on early 15 and possibly 16ACR alternators which had separate voltage controls. 17ACR and onward alternators (of the type fitted to Elans) had internal regulators and did away with the control box.

An RB340 is a Lucas control box for a dynamo, as is the RB106/2.

Thanks for the responses and discussion. I’ll check my switches, appreciate the confirmation on that.

My car has a new style small alternator from Dave Bean.

I did find a very helpful thread on options for the control unit, looks like removing it is an option to free up some space. Interestingly this individual had the same letter as I do and made the same comment that it was wrong on the S4 wiring diagram as well.

viewtopic.php?f=38&t=14326&start=&hilit=alternator%20circuit

Originality aside for a moment, is there a reason to keep the control unit or more reliable to omit it?

Thank you for the discussion.

tdskip wrote:I’ve also seen some cases where people have ditched the control box all together and simply connected the wiring absent the control box, that might be a bit neater I suppose but it seems like it might make troubleshooting more difficult?

Thanks!

Don't remove it, use it as a terminal block- it retains the original look while still serving a purpose I stripped out the guts so it's much lighter.

Post if you want instructions on what to do.

Tdskip,

Can you confirm which control box you have?

The picture you posted from the MGB manual was of a Lucas 4TR. These are rare:

https://www.ebay.co.uk/i/124252667752?chn=ps&norover=1&mkevt=1&mkrid=710-134428-41853-0&mkcid=2&itemid=124252667752&targetid=938697917246&device=c&mktype=pla&googleloc=9041123&poi=&campaignid=10204071741&mkgroupid=105678537727&rlsatarget=aud-629407027145:pla-938697917246&abcId=1145987&merchantid=263031448&gclid=EAIaIQobChMIy5rXnYqg7AIVmLPtCh0o5ALCEAkYAiABEgIKvvD_BwE

The most likely control box you have is a RB340:

https://www.ebay.co.uk/itm/Lucas-type-RB340-37342-12v-25A-voltage-regulator-dynamo-control-box/301435236712?hash=item462ef0b168:g:aV8AAOxyA4ZRMerm

Earlier positive earth cars were fitted with an RB106/2:

https://www.ebay.co.uk/itm/Land-Rover-Series-1-80-86-88-107-Lucas-Repro-Voltage-Regulator-Box-GEU603-217277/282516232219?hash=item41c747981b:g:k8kAAOSw~QRZ9KGV

What you can do, depends on what you have.

Andy.

Thanks for the responses, and hope I didn’t throw the conversation astray by posting an example picture for the new form member here. That was intended as an example rather than THE one I have. Sorry.

I will post a picture of my actual box but it is the AAA.... lettering one.

tdskip wrote:Thanks for the responses, and hope I didn’t throw the conversation astray by posting an example picture for the new form member here. That was intended as an example rather than THE one I have. Sorry.

I will post a picture of my actual box but it is the AAA.... lettering one.

OK, that sounds like the RB106. The RB340 was (apparently) a superior box, having an additional bobbin for current control - not that it matters in your case. I am surprised a RB106 was fitted to a '69 car as I thought they were obsolete by then, but that's the joy of a Lotus - 'bitsa this, and bitsa that'.

So, in answer to your original question, the control box is completely unnecessary with the alternator you are using. All of the functionality of the original control box is built into the electronics in the alternator.

You have two options,

1. (As suggested above) remove all the innards of the control box and use it as a fancy terminal block - this preserves the appearance and allows you to use most of the original wiring. You will need to connect some of the terminals together, there are threads which cover this.

2. Put the control box in the bin and run new wiring to the alternator. This is my preference - assuming the wiring is original (particularly the run of cable to the dynamo past the exhaust), after 50 years it is cooked, split and corroded. Depending on the power output of the new alternator, even in good condition the original dynamo wiring may not be up to it.

Good luck.

Thanks Andy, appreciate the detailed response.