Anyone know anything about the wiring of the brake fluid reservoir in an 86 ?

i was under the impression the light on the dash came on if the float dropped enough to complete the circuit. Touch the 2 wires together and the brake warning lamp is lit.

Is this the case?




i recently installed a later style brake master/booster. I assumed I could just connect the wires to the new plug and dash light would function.

however, with the wires connected the light on the dash is on even though the reservoir is full.

either the newer style works opposite to the original(that will be disappointing) or the float is faulty.

thoughts?

 

Google to the rescue.

so the float is likely stuck. I really wish i had flushed this thing and given it a good shake before I installed and filled with brake fluid

 

I have the 1989 Electrical Guide and it shows the fluid level sensor has four connections. Does the connector on your '86 have four pins? If so, see the attached page from the manual for the circuit diagram.

Cheers,

Don

 

The 1986 is only 2 wire. When float is up it is an open circuit, dash light is off.

The DB7 reservoir is the same, 2 wires. Open circuit when full.

unfortunately my float seems to be stuck at the bottom. Will probably have to drain fluid, take it off and shake it around.

the reservoir is NLA and crazy expensive if you find one so I hope this fixes it.

 

Ok, i know what my problem is.

the factory sensor is closed circuit when fluid is low, illuminating the dash light.

the DB7 sensor appears to work opposite, it is open circuit when low.

anyone have any ideas how to rewire to make this work?

 

If you can live without the low fluid detection, you could just disconnect the harness and seal it with tape...

I can envision a circuit using a relay so when the DB7 sensor opens, two contacts of the relay close, but it would take a bit of thought and time.

 

Thats what I was thinking too, but then Id have to build something, power it and it wouldn't look OEM+ like I was hoping to achieve. This was supposed to be easy haha.

 

You can make an inverter circuit with two resistors and a transistor.

 

I think the easiest solution is to wire in a Normally Closed 4 pin relay.

 

John,

That's a great idea! I notice that the circuit in your example link runs on 5 volts. What changes would have to be made to run on 12 volts? Could a simple voltage divider circuit give Nick a 5 volt tap for this circuit?

Cheers,

Don

 

I only dabbled in hobby electronics about 30 years ago, so am not a trustworthy source. That said, going from 5 to 12v necessitates higher value resistors. I think they'll have to dissipate more energy so spec accordingly.

If keeping an incandescent idiot light is a necessity, I'd probably figure out a way to get the switch to operate the desired way before I got into a relay.

 

Ive ordered a bosch relay, will know the results this week.

It works in my mind so far lol.

 

@nickr76 I think you have single-handedly boosted the value of DB7 manual pedal boxes with your mod. Genius idea!

 

This brake level sensor BS is driving me nuts.

installed a relay, powered it up. Seemed to be working.

now the float is working OPPOSITE to what it was before. Meaning its open circuit at full, same as the factory float.

i am about ready to ditch the brake fluid level sensor altogether.

 

If your draining it just get a new largeish plastic medical syringe.

 

If your draining it just get a new largeish plastic medical syringe.

 

I have a vacuum pump i use to drain.

i have now confirmed in the Aston shop manual, the switch is supposed to be “closed” when full and “open” when low on fluid(opposite to what my car came with so relay will be required)

mine is closing but it wont pass 12v through it, it will barely move the needle when I run a continuity test via multimeter.

i suspect corroded switch contacts.

 

this is way too much resistance at the reed switch. No wonder it wont trigger my relay.

i am going to attempt to replace the reed switch. While I am at it I am going to swap the existing “normally closed” reed switch for a “normally open” one.






getting to the part is going to be a challenge. Wish me luck.

 

Attempting an easier solution before i start hacking up the reservoir.

 

problem solved.

Genuine ATE cap with sensor.

40 bucks.