Adding Lights to a controller

Adding lights to a controller is relatively simple task but there are a few things that you need to understand first.

Beier, Servonaut and similar units

Units such as the Beier  and Servonaut modules switch the main battery voltage to the outputs, they are negative switching, which means that the control is done by switching the negative line to the load. What this means is that you can tie all the positives together and run one +ve bus back to the source. In order NOT to blow up the LEDs you need to use a resistor inline with the led, there is a calculator elsewhere on this site to help you with values. I tend to place a resistor in each  anode (positive) lead of each LED, this is regarded as best practice. You can then join leads for similar outputs together and run them back to the switched outputs.

Depending on the main battery voltage you can have some options. If you are using a 7.2 volt battery then to ensure that they always light up you should NOT series connect any white or blue leds. These have a working voltage that is commonly (but not always ) 4 volts. Orange and red leds can be used 2 or 3 in series if necessary. Series wiring means that the positive supply is fed to one led, the negative of that led is fed to the positive of another and so on. Only 1 resistor is required for the circuit. White leds can be succesfully series connected for supplies of e.g. 11.5 volt batteries.

Connecting OEM accessories to these units means that you have to pay attention to any provided instructions and connect in parallell or series and and the necessary resistor.



MFU's are a little different in that they have circuitry to boost the voltage available to led outputs. For white light outputs this is around 8 volts and the leds must be series connected so that they are not blown. e.g. two white led's in series. You cannot connect coloured leds to these outputs. The brake outputs have a supply of around 4 volts and again red led's mut be 2 series connected. Amber outputs tend to be for single leds.

The MFU also has current limiting on the led outputs and this is around 100 ma. That in general means that you can drive maybe 5 sets of leds from a single output BUT be aware that doing so may invalidate your warranty. In practice adding a second and maybe a third set is fine. Bear in mind that the MFU has an overall limit to its output so dont go mad adding lights. Use an rc switch on a spare channel instead.

You can add coloured leds to a white output but you will find that doing that directly may blow the leds and/or will stop the existing ones working as the voltage is dropped to low. You can overcome this by adding a resitor in the coloured led circuit.


Lighting systems

Lighting systems are different again in that they generally employ led drivers and drive single leds, Some will support a second set of leds but some like the GT power will in general not. ( The GT power has an output limit of 30 MA and a bright LED needs 20ma).


RC Switches

Rc switches can be treated in the same manner as the Beier and Servonaut units in that they switch the main battery supply to the load(s) there are many but the best (IMHO) are the graupner SXM and the BEIER switches.

The Graupner SXM has 4 4 amp outputs that are configurable as flashing, momentary, or on/off. These use one channel and a selection of timings to select which output to switch.

The Beier unit again has 4 4 amp outputs and switches in a similar manner to the SXM but also has multiple working modes.

You will need to add resistors to LEDs for all these units.


OEM add ons

Add on units such as the DMW light bars and bumpers, usually have separate leads for each led set.  Be sure to check! you can do this with a high value resistor ( 1k) and a battery , you cannot blow the leds with a resistor in circuit!  How you wire and connect depends on the unit you are connecting to. For MFU wire left and right brake lights and reversing lights in series and plug in. indicators just plug in. For other modules follow the advice above or you could have an expensive mistake on your hands.