On a 1988 Toyota 4runner, does the brake light on the dash indicate the parking brakes are set or the brake fluid level needs attention? The brake light on my dash stays on as long as the engine is running. The parking brakes are released but i've noticed that when I remove the brake fluid reservoiur cap the light goes out. You can activate the float in the reservoiur and the light will go off and on. I would think the brake light should come on when the fluid is low but the reservoiur is full and the light is on. All the vehicles i've previous owned, the light meant the parking brakes were set. Is the light staying on normal or is there a problem somewhere?

 

Yes. Either one. If playing with the float in the reservoir allows you to turn the light on and off, you might have a "waterlogged" float that sits too low, or a bent mount.

I don't think there is a replacement for the float or switch alone, but RockAuto has a new (aftermarket) replacement for the whole master cylinder, including float/switch, for $36.

 

Shouldn't the light come on when the fluid gets low instead of being on when full of fluid and going off when it gets low on fluid? The master cylinder was replaced several months ago but the light only recently came on. The light seems to be working backwards from what you would expect.

 

Based on all of the above, I second Scope ^^^. Maybe your level switch is bad like he says.
To eliminate doubt/prove that switch is bad, disconnect the brake fluid reservoir level switch and see if problem persists.
If problem persists, inspect the e-brake release switch.

 

It does sound like the float is sitting to low.

I most likely have a few sitting around if the OP figures that is his problem.

I can send them a switch if they PM me the address

 

I had good luck by taking the top black cap off of the Brake Fluid reservoir cap... there is a removable black top on the top of the cap...and cleaning off the brake fluid from the electronic sensor. I think what happens is that brake fluid leaks onto the circuit board and shorts the sensor which then triggers the "ghost" brake light on the dash.

 

Yes, That's^^^ a possibility.

 

The switch appears to be working fine but seems to be working backwards. With the reservoir cap removed I can move the float up manually, as if the reservoir is full of fluid and the light comes on. I can move the float down, towards the bottom as if the fluid level was low and the light goes out. If the float was waterlogged wouldn't that make the float sit lower in the reservoir and cause the light to go out? I can also disconnect the plug going to the float and the light goes out. Although moving the float up and down turns the brake light on and off would it be best to just replace the float to determine if this is the problem or that I have problems elsewhere? Thanks again for all the advice.

 

Then the problem is definitely the float switch.
What Go Blue means above is fluid/water has contaminated the switch contact and causing it to short.
However, because you say the switch works backward, then we know something is wrong with the switch. Contact could have mechanical damage.

 

Wrong cap, wrong tank, wrong master cylinder..

I vaguely recall they switched these around 92?

 

I know it's supposed to indicate low brake fluid but if brake fluid is okay lube the parking brake cable. It fixed mine.

 

Hi Nervo,
Not the parking brake switch, according to below...

 

Interesting. I replaced my MC on my 86 with one from a 92 V6 T4R and since the cap doesn't match the original plug I just never connected it. I expected the light to come on, at which point I'd just splice the old cap connector onto the new cap (might still do that) but since the light didn't come on I haven't done it yet.

 

Logically, a switch for most warning lights would complete the circuit IF, and only IF, there is a fault condition.
Brake fluid level switch should also complete the ckt to ground when level is low.
Parking brake error switch also completes ckt to ground when park brake is not released completely.

A thousand words follow...

 

Good wiring diagram as always, RAD4Runner.

Since the fluid level switch completes the circuit when fluid is low, the light should never come on due to that switch being disconnected. The parking brake switch can still turn on the warning light.

I would connect the master cylinder fluid level switch if I were you. You don't want to find out the hard way that you have no more brake fluid!