Rostra cruise control cutting out

I have a rostra universal cruise control. I live where it get cold and mine worked fine for 6 months, roughly and it has started acting up. When the car has sat overnight it will engage and work fine for about 5-7 minutes and then stop working.

Originally at that time the brake light fuse blew. I changed it and that's when it started doing only working 5-7 minutes.

I have the switched 12 volt from the ignition on a very low fuse - I think 2 or 3 amps. Could this cause problem? (its in a diesel only using vss signal for speed as per rostra tech)

Its in a 99 vw golf, with a 1.9 tdi (cable run pump or Mtdi)

What system do you have installed so that we can look up the parts to help you trouble shoot.

I'm not sure what system your refering to - It's a Rostra 250-1223 Universal Cruise Control Kit with using the original VW control stick for set/coast and on/off/resume - those are the two selectors. Ground is to the battery - the switched 12v is the one I'm wondering if its not getting enough power with a 2 or3amp fuse.

I'm not sure what else to mention - it's a cable control that runs parallel to the throttle cable and connects to the deisel injector pump throttle lever.

Like I say, once the car has sat a while it will work fine for 5-7 minutes and then stop. It won't resume after that either by using resume or set/coast button.

Oh yah, it also uses the VSS from the VW (VDO speedo provides power to the VSS - custom gauges in the car), original brake wires connected for the brake function (that was the fuse that blew - after replace now this problem) - 2 connection wires for set/coast and resume/accel/on/off - I think that's all the connections to the car.

Fuses blow for a reason. It is possible you have a wiring problem. Check the red and the brown wires at the cruise control module with a volt meter. The red should have 12 volts battery and the brown 12 volts ignition power. There are 2 intermediate connectors inline that may have poor connections too. The violet wire for the switched side of the brake circuit must have less than 10 ohms resistance to ground with the ignition ON. If the brake lights are working correctly or have been changed to LED units, this will cause problems. It is also possible the unit has gone defective. The best way to check is once it fails, do an electrical check without turning the ignition OFF.

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sparky

thanks. this at least gets me a starting point. I will check the switched 12v as I'm thinking it might be suspect. I have LED back lights, so I will check that as well. What can be done to reduce ohms if its too high? run a wire straight from the back of the car??

No. The purple wire from the cruise control that goes to the switched side of the brake switch must have a low resistance reading to ground for the cruise to work. It gets this by being connected to the brake lamp bulbs. When they are not powered (brake lights on, brake pedal depressed) they receive a ground through the bulb filament. It's done this way for safety. If the bulbs are burnt out the cruise will not function. The LED style lights do not provide this path to ground. You can wire a relay into the circuit that provides a ground signal until the brakes are applied. This will fix your issue, but install the relay inside the vehicle and in an area where you won't hear the relay click when the brakes are applied. Wire it as: terminal 86 to switched 12 volts from brake switch, terminal 85 to ground, terminal 87a to ground, terminal 30 to the purple wire from cruise control and terminal 87 is not used. The relay will activate (click) every time you press the brakes, so make sure to put it somewhere it won't be heard.

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sparky

I tried to hook up relay as suggested, I'm assuming the relay was bad because I kept blowing a the brake fuse.

I reviewed all connections anyway with the cruise instructions and double checked I was getting at least 12 volts (car off) and the (I believe brown wire) was getting just over 12 volts.

the purple wire was -.065 volts or so on voltage check to ground with brake not drepressed and about 9.65 volts brake pedal pressed. Would this have an effect on the cruise - the less than 12 volts brake pedal pressed?

Anyway, for some reason it's working again??? I don't know what happened to change/fit it

Just an FYI - my tail lights are led, my brake lights are regular bulbs.

Thanks for your help!