1972 Dash Brake Light

[kna4977]

Was messing around in the engine bay and the electrical plug that goes on to the switch on the master cylinder didn't seem to be fully on, so I pushed it down to where it would seat. Dash brake light came on and stayed on.

Took the plug off and someone at some point had put tape on it I assume to keep it from staying on all the time. I retaped it and put the plug back on. The dash light comes on when the key is first turned on then goes off like it should. I believe this is how it is supposed to function, but don't think tape would have ever been involved originally. What do I need to look into to get it working like it should when fully connected without tape interrupting the circuit?

As far as stopping goes, the truck does like I think it should.

[vics stuff]

If I am correct , I think the dash brake light that is tied to the proportioning valve on the master cylinder , is telling you that there is a difference in pressure between the front and rear brakes and either the system needs to be blead or there is something going on inside the brake cylinder. I had found this to be the issue with my all stock 72 two wheel drive .
The light should not come on at all even when initially starting your engine . Something is going on

[zosoppp]

Originally Posted by vics stuff

If I am correct , I think the dash brake light that is tied to the proportioning valve on the master cylinder , is telling you that there is a difference in pressure between the front and rear brakes and either the system needs to be blead or there is something going on inside the brake cylinder. I had found this to be the issue with my all stock 72 two wheel drive .
The light should not come on at all even when initially starting your engine . Something is going on

There is a bulb test circuit for the brake warning light and the temp warning light when the key is in START (not run). It should be off at all other times.

[PbFut]

You likely have a out of balance brake system as noted above. Searching will yield decent info on subject. It could also simply be the switch. Removal will not cause leak. Testing is simple. Inline tube has both style replacements. If the suttle valve is tripped causing light swith to trip, you are only stopping with half your brakes and you need to figure out the problem.

[dmjlambert]

I recommend follow the brake warning light test procedure on p 5-23 and 5-24 of the 72 service manual. If you don't have the manual, a PDF version is available here on the forum.

But first if your brake hoses are old, replace them and also check that you can bleed all 4 brakes and fluid flows very well, and if it comes out at the brake cylinders/calipers dirty or different color than what is in the master cylinder, flush out your brake system with new fluid completely.

Back to testing the switch, to reset switch, apply heavy pedal force. This force will apply hydraulic pressure which re-centers the switch contact. The manual says failing the check the entire combination valve must be replaced, but if you have an original, I don't recommend doing that or you will be stuck with one of those brass block style junk from China and you may join the many people complaining here on the forum about leaky or faulty combination valves. Instead send the original off for restoration at White Post Restorations. I did a lot of reading here on the forum before deciding to get an original and send it to them.

[davischevy]

Originally Posted by dmjlambert

I recommend follow the brake warning light test procedure on p 5-23 and 5-24 of the 72 service manual. If you don't have the manual, a PDF version is available here on the forum.

But first if your brake hoses are old, replace them and also check that you can bleed all 4 brakes and fluid flows very well, and if it comes out at the brake cylinders/calipers dirty or different color than what is in the master cylinder, flush out your brake system with new fluid completely.

Back to testing the switch, to reset switch, apply heavy pedal force. This force will apply hydraulic pressure which re-centers the switch contact. The manual says failing the check the entire combination valve must be replaced, but if you have an original, I don't recommend doing that or you will be stuck with one of those brass block style junk from China and you may join the many people complaining here on the forum about leaky or faulty combination valves. Instead send the original off for restoration at White Post Restorations. I did a lot of reading here on the forum before deciding to get an original and send it to them.

What he said.