Signs and symptoms of a bad vac pump

[hdjeff]

e brake is up all the way and wotn move any further, which one is the sending unit on the master cylinder? there are two wiring harnesses, one on the leading edge of the master cylinder on the log looking thing where the brake lines run off of, or the one at the bottom of the resivoir.

 

[action4478]

Bottom of the resevoir. I have been told these can malfunction

 

[hdjeff]

figured that was the one, i will try to check it out soon, if the dash light is on and i disconnect to harness, would the light go out or stay on???

 

[action4478]

I 'm pretty sure it will stay on. I'm not sure where it gets it's ground. The sending unit is only a switch to say you are low on brake fluid. If the light is on for another reason unplugging it won't make any diff. You can test the unit by removing the brake fl & reading the switch with a meter before removing fl & after & see if you get a different reading,You also may be able to just cross the two leads by unplugging the wires & use a jumper wire to remove that variable. THe only time I ever got mine to go away by doing something was when I messed with the E brake switch. I finally forced it to stay open phisically. The light still stayed on .One more thing, I'm not sure if the switch is normally open Or normally closed. That will make a diff whether you can bypass it with a wire or not.

 

[hdjeff]

what does the other wiring harness do thats on the master cylinder?

 

[action4478]

I think that is the one that tells you that your braking pressure is going away.( usually when you least expect it, but always after it happens)

 

[hdjeff]

lol, thats good, another idiot light when its too late. thanks for the info

 

[deereman39]

If you are refering to the switch on the end of the master cyc it is for the cruise control,has nothing to do with the brake light.Try on hooking the wire on the park brake lever and see if it goes out.
Cheers Ed

 

[hdjeff]

the cruise control is still affected when the brake light comes on, maybe this might have something to do with it. sometimes when the cruise is set, it will stop and then you see the lovely brake light on. if the light is on, cruise wont work at all.

 

[deereman39]

That switch on the MC is a cut off if the brake light switch fails,you can put a jumper wire in the connecter and see if it makes a difference.I have mine jumpered all the time as this is the switch that causes all these trucks to catch on fire.
Cheers Ed