Hi, I have been working on this 96 4X4 dually w/ rwal and need some help. Both brake lights are on, red and yellow ABS. There is no fluid level sensor, the Ebrake's is open, and brightens the red light slightly when applied ( grounded). The proportioning valve is centered ( not grounded on the valve)
What I don't know is why the Haynes manual doesn't even show a vacuum switch. There are 3 wires and I don't know which ones need to be shunted to troubleshoot? If I was low on vac would both yellow and red lights be on? The service brakes feel right. I have grounded momentarily term 13 on the Diag. plug, and no codes are flashing. I also, have disconnected the batts overnight and when I started it both lights stayed on. I would think that for a tone sensor in the Axel would need to be driven to set a code? The only way to get the ABS light out is to remove the underdash controller, and red brake light stays on.
Could someone help me eliminate the vac sensor, by shunting wires or is the switch a pot, as there is 3 wires on it? What is the normal range of vac for this switch to operate? 5 - 12 maybe? Or send me to good thread? I know I would appreciate this, as well as my Dad and brother. Thanks for some direction Artie

 

art.. both warning lights will stay on if you have low vac or a bad switch. if vac falls below 8.5 it will set switch. you can find out a lot if you test vac switch with a hand vac pump. if rear wheel sensor is bad it will do the same thing. make sure that engine vac pump is producing vac. hope this helps.

 

Paco. My mighty-vac shows 5 in. vac, however, I can't draw no more than 6 or so with my mighty-vac... Need a new one or get mine fixed, asap. I DO have a low vac condition, though. Back out to the garage for more testing, Thanks, Artie

 

got it! chapped hard vac line going to the cruise servo! I'll have some ice cream and celebrate! Thanks for the 8.5 vac tip Paco 72.