light sensors and remote revving

What do you wish this "simple light sensor" to do?  Turn on the headlights when it's dark..or another purpose? If for the headlights you can buy an aftermarket setup...they are not expensive so IMO not worth the hassle of building it yourself. But thats just me.

The newer cars without throttle cables at the accelerator pedal are called "drive by wire"..If you wish to control the vehicles "revving" (I assume this means RPM) you will need to rig up whatever it is you do at the accelerator pedal...perhaps a linear actuator w/ cables and pullies...I would have to see the specific vehicles accelerator pedal control to accuratly advise how to do this...safety being a major factor...you don't want anything binding up or catching your foot while driving..that can never be a good thing.

Can you explain how you were doing this before?  Where you using a cruise control servo or something like that?

If you do wish to build a light sensor here is a link to a basic setup. It can be used to trigger a relay when it gets dark..or when it gets light..depending on your needs.

http://www.uoguelph.ca/~antoon/circ/sensor2.htm

Or you can purchase something like this or similar....DEI part # 545T nite-lite system. about 35 dollars US retail.

  It will automatically energize the vehicle's headlights and parking lights whenever it becomes dark, or whenever the vehicle's windshield wipers are turned on. If used with a security system, the 545T will turn on the headlights and flash the parking lights on arming and disarming if it is dark. It can also be activated and deactivated by one of the security systems auxiliary channels.

I still do not understand what you are doing with this light sensor. You are worried about the current draw of the relay..but..a light will certainly draw more current then a relay coil.. Unless this is just for an LED? If you are using this to turn on the headlights while you are driving and it gets dark the DEI turns off whenever the vehicle is off so current draw is not an issue. Perhaps you can explain more specifically what you wish to use this for and I can help.

Also why would a cruise control servo be too "weak"...nothing is better designed specifically for opening a throttle. BTW is there a specific reason you want the car to rev by remote (such as voltage increase) or just the "cool" factor?

Ok..now I understand what you are doing...a cruise control servo is not nessecary if this is just for show...they are vaccum operated and are controled by an electronic module the monitors speed etc..you would need to do some enginnering to get it to operate and an acutator is so much simpler...press and pop..thats all you really need for a display vehicle. Now as far as current draw..most batterys can not last overnight with more then 20ma max..so are you doubled up on batteries? and hopefully using deep cycles on something like this.

My other question is....if you are using this "revving"..that means the engine is running. So the alternator should be charging the battery(s). Just start the car every so often..that should eliminate the current draw from killing the battery.

As far as the remote start in the golf5....we do not have those in the USA. My sources tell me that an immobilizer is not available for that vehicle..you would need to check sources in your country..it must be something weird. I can tell you that late model German made vehicles can be a pain to do a remote start in..there are a few we have not been able to do even when a programmable bypass mod is out there listed..it just doesn't work and no one has yet figured those out 100%.

As far as voiding the warranty I am not sure about the laws where you are..in the US a warranty MUST be honored UNLESS it is proven the device installed caused the problem. So to answer your question you may have been right in telling him this..can't say for sure..probably a good call I would think.

Well the "computer controlled accelerator" as you call it would not be a problem with a remote start installation..the RS simply mimicks what the key does.

The problem with doing a remote start in that vehicle is finding the right bypass module to allow crank, if there are any available yet that can do that golf..