unexpectedbill Posted October 4, 2018 Share Posted October 4, 2018 Hello all... I have a 1989 Mack R690ST model truck that was converted into a grain hauling truck with a dump bed. All the time I've owned it, the parking brake indicator light has never functioned. I've recently been looking in to why that might be, and have confirmed that the bulb is good and that there is power coming to it. In going through the circuit, and looking at some of the other warning lamps (low air pressure) it appears that the bulb grounds are what is being switched. I've had no luck so far in finding the actual switch, assuming it still exists. There's no doubt that someone has been goofing around with the wiring on this truck over the years. I inquired at an area Mack Truck service facility and dealer, but they haven't been able to help me. Web searches haven't produced anything useful either. I am very much hoping that someone here could point me in the right direction. Quote Link to comment Share on other sites More sharing options...
Vladislav Posted October 4, 2018 Share Posted October 4, 2018 Are you sure your service brake lights (at the rear end of the truck) are working? I can tell you a small switch on the firewall just behing the engine rear head is what activates the service brakes light. And they light on when the parking brake is applied either. Sorry can't tell about the particular switch you're asking about. From my memories it is attached to one of the dash brake valves behind the dash face panel. But I'm not 100% sure at the moment, didn't tinker with. Quote Никогда не бывает слишком много грузовиков! leversole 11.2012 Link to comment Share on other sites More sharing options...
unexpectedbill Posted October 4, 2018 Author Share Posted October 4, 2018 Yes, the service brake lights do work when the pedal is pressed. Someone may well have replaced the parking brake switch in the dash with another. I did look around behind that part of the dashboard for any wiring that might have gone to the control, but I did not find any. I will try to get some pictures. Quote Link to comment Share on other sites More sharing options...
Mackengine Posted October 10, 2018 Share Posted October 10, 2018 the switch should be on the parking brake valve. I have seen guys take them out when they go bad and put a plug in place of it . Quote Link to comment Share on other sites More sharing options...
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