Brake Fluid Switch

[BillyRok]

A while back I swapped out my stock front MC for an aftermarket one with a bigger bore as I delinked my braking system and thought it might be wise to push more fluid now that the MC was working both front calipers. This resulted in 2 minor annoyances...the right side mirror mounts at a different angle from the left side (bugs me every time I look at it) and there is no wiring for the low brake fluid sensor that is stock on the XJ so the "Brake" warning on the dash is on all the time. The original MC isn't usable so I found one on Ebay, got it all hooked up and bled the system so now the mirror looks right but the warning is still on. Here is what is inside the MC --

[IMG][/IMG]

The post goes up through the bottom of the MC reservoir and the o-ring seals it. A screw goes through the little "foot" on the right and is threaded into the bottom of the reservoir inside of it. Then we have the rectangular styrofoam float with a little "donut" magnet in the middle of it that slides over the post, it is held on the post by an E clip fastened to the top of the post. So knowing very little about electricity I start fumbling around. Here is what I get when checking continuity with the float at the bottom of the post (which would mean fluid level is low)--

[IMG][/IMG]

And this is what I get when the float is at the top of the post, indicating the fluid level in the reservoir is full--(can't get PhotoBucket to turn the pic right side up)

[IMG][/IMG]

Does all this mean the circuit is open when the level is low and there is no continuity? And the circuit is complete when the level is full and we have a tiny bit of resistance registering? How can the fluid warning be on when the level is low if the circuit in not complete? Any insight you can give me to help remedy this is greatly appreciated, thanks.

[crazy steve]

...Does all this mean the circuit is open when the level is low and there is no continuity? And the circuit is complete when the level is full and we have a tiny bit of resistance registering? How can the fluid warning be on when the level is low if the circuit in not complete? Any insight you can give me to help remedy this is greatly appreciated, thanks.

That's a 'fail-safe' circuit; if either the fluid is low or if the sensor/wiring fails, the light will come on. In your case the sensor has failed. If you look carefully at your meter, you have more than 'a little bit' of resistance. What you have is 269,000 ohms resistance; note the 'M ohms' at the top of the readout which is 'meg' or million ohms. That's high enough that the computer will read it as open.

Try connecting the two wires from the computor to the sensor together, that should turn the light out.

[BillyRok]

Yeah Steve, I guess 269,000 ohms is more than a little bit of resistance! So if the sensor was working properly and the reservoir was full, there would be zero resistance and the circuit would be closed and the warning goes out? I'll try connecting the 2 wires together that the sensor wires connect to and report back.

Do all the dash warnings/computer checks work the same way...the warnings come on and stay on only when there is an open circuit? Reason I ask is that I have a couple other issues with the 2nd XJ I have (think it's sold, guy supposed to pick it up tomorrow). I have the same "brake" warning on all the time as well as the "battery" and "fuel" warning. The FSM says that the fuel sending unit reads higher and higher resistance as the fuel level gets lower...the warning is always on so the sender is shot? Can I just connect the wires the sender plugs into to bypass it and turn off the warning? The battery water level probe in this bike is shorter than the one in my XJ (maybe it snapped off?) so I don't think it reaches the water in the cell even if it is filled to the proper level, although occasionally the warning does go out. Can this sensor also be bypassed to turn off the warning and if so, how? Appreciate the help!

[TopCatGr58]

Bypass XJ battery warning light!

http://www.xs11.com/forum/showthread.php?t=668

T.C.

[crazy steve]

Ok, after going back and reviewing the XJ manual, here's my take on all this...

According to the manual, the brake warning light switches are just that, simply switches. They should read zero ohms (or close to it) when the float is down, open when the float is up. So it's not a failsafe circuit. Now, I will say this with a grain of salt, because the diagram as shown is incorrect; the way the manual shows it, you'd only get a warning light if both reservoirs are low. The easy way to check this is to simply unplug the low level switches; the warning light should go off. If you connect the two wires from the monitor to the switch together, it should go on. If this test makes no difference and the light stays on, then the problem is in the monitor. About all you can do there is check/clean connections to and internally at the monitor, if that doesn't clear the problem then the monitor has an internal fault and needs to be replaced. I would check to make sure the 'reset' switch is working also; it it's not, you may be looking at 'stored' codes, not current problems.

Pretty much the same thing for the low fuel light; if the fuel sending unit is working correctly and the connections to the monitor are good, then the problem is in the monitor. Is the fuel readout working? If that is, then the problem is definitely in the monitor.

If the monitor is screwing up, then the 'battery bypass' may not work. Just for the hell of it, you might try picking up some 20 ohm resistors (same as you need for the battery bypass) and try connecting those across the brake switch and fuel sender leads from the monitor. If that turns out the lights, then it's the fuel sender/switches at fault.

[BillyRok]

Ok, first off, thanks TC and Steve for trying to help me sort this out. Now upon further pondering I've figured out the problem...turns out I may be a dumba$$. Hey I know, I'll tell you what I did and then we'll put it to a vote!

First I followed Steve's advice and disconnected the Front MC fluid sensor and put a jumper between the White/Black and Black wires coming into the bucket that the sensor connects to, and.......nothing, the warning is still on! Crap, Steve always knows how to fix the electrical bugs, now what???

I was looking at my big, pretty, color 16x22 XJ wiring diagram that I bought on Ebay and noticed 2 brake fluid level switches. Odd I thought as I only have 1 switch, it's on the front MC. Must be another mistake like we see from time to time in the manuals, somebody goofed up. So now I read Steve's 2nd post and he also mentions 2 switches. OK, let's have a look at my old parts bike and the other XJ (just sold it today) sitting here and compare to my bike. Then it hits me. The rear MC sensor plugs into 2 White/Black wires just like the diagram shows. But on my bike when I delinked the braking system, I replaced the stock MC and proportioning valve with a MC from a '79 which of course has no sensor in it. I start rooting around and low and behold those 2 White/Black wires on my bike are just dangling there tucked away between the battery and the battery box. As soon as I put a jumper across them, the brake warning goes out, yippee!! So once again it appears the problem can be traced back to the big nut behind the handle bars!! Polls close at midnight.

PS - I expect the guy who bought my other XJ will be joining this site soon. If he's half as anal as I am he'll be looking for help getting his warning lights to go out. I say we help him fix his own bike so I can get on with my life!

[crazy steve]

Interesting..... so it is a failsafe circuit after all, and the FSM is murky at best....