Lotus Elan

Headlamp pod vacuum using a solenoid not dashboard switch

PostPost by: Bigbaldybloke » Sun Sep 03, 2017 10:25 pm

I've searched as best I can and found one reference to using a solenoid to control the vacuum to operate the headlamp pods. Mine is an early plus 2 chassis no. 142 which originally had vacuum to put the headlights up. Many years ago I modified it to failsafe using just one vacuum pod and this worked fine, I used a hillman imp steering column tube with brackets on each end to link the pods. I have now bought the proper lotus design linkage and was originally planning to motorise the pods with an MX5 motor and have made up a prototype bracket to mount it, but am having second thoughts on this. I'm now thinking of retaining one vacuum pod and springs as per the lotus failsafe design. The difference I'm considering is using an electrical solenoid to switch the vacuum on/off rather than piping it back to the dashboard operated vacuum switch. Has anyone more details on this, what solenoid was used and how it was controlled, I'm thinking of taking a feed from the headlight on/off switch to operate this solenoid so that just switching the light switch to headlamps turned them on and raised them with just this one action. My car has the later spot lamps under the bumper and I've put in relay logic so that if I flash the headlights when they are down, the spot lights flash and if the headlamp pods are up then the main beam flashes. I'm undecided whether to do away with the panel light switch and use it for the spotlights or if I go the solenoid route then fit an additional switch in its place for the spotlights. I also have to find somewhere / somehow to operate the electric screen washer pump, at present there is a long shaft toggle switch on the hole where the choke cable should be as just a couple of pumps on the throttle pumps enough fuel into the Webers to make the choke unnecessary. I'd like to reinstate the choke, but having the washer switch there is very ergonomic. All comments welcome.
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PostPost by: paddy » Mon Sep 04, 2017 12:31 am


There was some discussion here: lotus-twincam-f39/heater-valve-t17647-15.html#p92704

The link to the part in that post is now moved to https://www.zoedale.co.uk/sirai-l340.html. In my case the solenoid is wired to activate via the lights switch and it's still going strong after nearly 10 years.

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PostPost by: vxah » Mon Sep 04, 2017 7:50 am

if you look in the service manual you could use the later wiring schematics to figure out the circuit that Lotus used for the failsafe system. The solenoid to operate the vacuum I think was a bespoke unit back in the day? It has a ball inside to seal the air but this ball tends to degrade with age and then does not seal properly so, beware of old oe solenoid valves! Other solenoid valves that look similar are available if you search but, one thing to remember is that it needs to flow quite a lot of air if you want the lights to come up at a reasonable pace, as in if you flash the lights and the pods creep up a little then down again before getting anything like pointing forward?
The original wiring only allows headlamp flash with the dip switch in the main beam position, or that's what I thought for 30 years then, I found that actually they do flash if the flasher switch is used in the dip position (lights off) but the pods don't lift! Checking the circuit diagram shows it was done that way to stop voltage feedback, adding a couple of diodes and some relays will allow brighter lights and full flash operation!
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PostPost by: gus » Mon Sep 04, 2017 1:22 pm

IIRC in the original wiring, the dash switch provides ground to the headlight relays, and the dip switch switches power to low or high beam. It has been a while tho.....

If this is so, one could wire the solenoid[which I have done, but 25 years ago] to be powered full time and provided ground with the relays.

If I am mis remembering then at any rate, there are two microswitches on the dash switch, one for sidelights, the other one you can use to power the solenoid in whatever way it is functioning

Solenoids are not cheap but not that hard to find, just a 2 way 12 volt solenoid, also used on other cars of the period
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