dashboard powering during start-up

[theV]

Hi to all,
I posted here because it concerns power lines around the dashboard, but if you think the more appropriate section is another (Ownership Problems etc.), please move the thread and/or change its title!

Foreword:
I have a LandiRenzo Omegas LPG fuel system installed. This (but surely other brands' ones too) bears an option called "emergency gas startup".
It means that, if I run dead out of petrol, theoretically I'm still able to start the engine directly from LPG (instead of petrol as default), of course provided that the environment/coolant temperature is reasonably warm.

The procedure is as follows:
- turn on ignition (without starting the engine)
- depress for ~5 seconds the LPG/petrol button on the LPG control commutator on the dashboard (wherever it has been installed) and wait for a confirmation beep and a change in LEDs status
- now the LPG system is set on "gas" and it's possible to start-up the engine (straight from LPG).


Problem with Megane and its keyless crank up is:

as soon as I press the engine START button, most of the dashboard is briefly turned off, including the LPG control module which then restarts with default behaviour
Maybe this is not (for once...) a car-related problem, but rather an installation one.

Therefore I need a 12 V source which is:
off when the car is dead off (e.g. closed),
on when it's on, and as soon as I press the START button (wihout depressed pedals),
and finally on DURING the engine's few startup seconds.

Is there such a wire, in the booth/dashboard or in the engine bay? Where?

Thanks for any help/comment

[Paddy]

Yes the positive lead to the 12V cig lighter meets these criteria.

Although i would wire it to the 3rd wire of the cig lighter. It turn the light on and off.

That means to power up you LPG control you would flick on the side lights at the stalk giving you 12V.

That would work.

[theV]

Hi and thanks for your interest!

I apologize for the very, very late reply

I carefully measured voltage with a multimeter, and unluckily the cigarette lighter (both the "hot" lead and the illumination one) completely shuts off (0 volts) during engine crank-up.
Therefore it is not suitable to my task.

[davelowe]

You could use Paddy's suggestion with a modification.

Wire the LPG system from the cigarette lighter as mentioned but also take a feed from the starter solenoid. With some diodes and a largish capacitor to cater for the switch over in feeds you might be able to make it work.
10,000uF
Earth --------| |----
D1 |
Lighter socket ------>|------- LPG System
D2 |
Starter solenoid ------>|------

Diodes (1N4001 or similar) will cause a 0.6V drop, but you should get around 10V while cranking to the LPG. Bits would cost <£1/Euro/$

[theV]

So basically you suggest kind of double, parallel feed...
the usual "unsuitable" cigarette 12 V AND the solenoid live.
When one is off, the other is on (e.g. during startup) and viceversa, with the diodes preventing a short between the two.
Clever!

I'll suggest it to my LPG mechanic (who's not a Renault expert) as soon as I visit him.

Thanks