Intermittent brake warning light - Alfa Romeo Bulletin Board & Forums
 
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post #1 of 8 (permalink) Old 09-20-2019, 10:55 AM Thread Starter
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Intermittent brake warning light

As I slowly debug my new 1974 USA spec GTV, I’ve got a new one.

Brakes work great. Hand brake & electrical circuit works correctly.

Issue: dash brake warning light intermittently comes on and goes off. It’ll come on while driving (but not touching the brakes), and go off a couple minutes later. After 5 min it comes on again, only to go out 2-4 min later. Did not do this when I test drove the car last fall.

Does it even when I disconnect the hand brake switch. Brake fluid is topped up.

Ideas anyone?

John F.

Last edited by bfeng; 09-20-2019 at 11:45 AM. Reason: Left out important info
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post #2 of 8 (permalink) Old 09-20-2019, 11:19 AM
But Mad North-Northwest
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Well, you don't mention the year, but the brake warning circuit runs through the brake MC reservoir float(s) and the brake pressure differential valve (if you have one.) If any of those ground the orange wire, or the orange wire grounds to chassis somewhere, it'll light the light.

You'll need to do some troubleshooting and probably trace the wires looking for brakes. You can also try unplugging the circuit at the various point sin the MC or the differential valve to see if that can help isolate the problem.

Could also be the parking brake wire or its switch so check those too.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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post #3 of 8 (permalink) Old 09-20-2019, 11:55 AM
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Check the pressure switch (mentioned by Gubi) on the brake circuit manifold located along right side of the engine bay near the SPICA fuel filter (you're '74 should have one). There's an orange wire that connects to the switch. Pull the wire from the switch if your light is on and see if it goes out. If so, the switch may be stuck or plugged with debris.

Ken
'73 GTV
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post #4 of 8 (permalink) Old 09-20-2019, 12:29 PM Thread Starter
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“Pressure switch”

Is that the one underneath the ignition coil at the right rear corner of the engine bay? I noticed an unconnected pressure sender on what appears to be a fluid manifold, and a whitish wire that was just dangling near by. Perhaps the sender is bad & the PO or his mechanic just pulled the wire off to extinguish the light?

Im going to disconnect the fluid level senders, and tape that dangling connector, and try it.

John F.
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post #5 of 8 (permalink) Old 09-20-2019, 12:44 PM
But Mad North-Northwest
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That sounds like the manifold where the differential pressure sensor is, yes. If the wire's just flopping around and grounding on things that could be your problem.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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post #6 of 8 (permalink) Old 09-20-2019, 12:44 PM
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Yes, that's it located under the coil and very near the rear end of the SPICA air box. But there should be an orange wire (unless the wire insulation is badly faded).

Ken
'73 GTV
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post #7 of 8 (permalink) Old 09-20-2019, 01:54 PM Thread Starter
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Quote:
Originally Posted by Gubi View Post
That sounds like the manifold where the differential pressure sensor is, yes. If the wire's just flopping around and grounding on things that could be your problem.
Connected wire to switch. Same problem. Will remove switch to see whatís going on inside the center chamber. Most old cars donít have pressure differential warning systems so I might go without if there is no easy fix.

Taped of connector to prevent grounding and now the warning light is off all the time. So indeed someone took a shortcut on the Sifferential pressure switch. Itís consistent with the short cuts taken on the Spica, and proof that you can get one of these to drive well with short cuts rather than fixing them the right way.

Practically speaking I understand this approach but itís not my cup of tea. Looks like Iíll be doing some tear down and fixing over the winter.

And yes the wire is ORANGE, and my memory was faulty

Thanks all

John

John F.

Last edited by bfeng; 09-20-2019 at 03:51 PM.
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post #8 of 8 (permalink) Old 09-20-2019, 02:00 PM
But Mad North-Northwest
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I wouldn't remove the switch, no: you might wind up with a fluid leak or something. The way it works is if there is a difference in pressure between the front and back brakes (because of a leak) then switch grounds the orange wire. If the warning light is lighting with the wire disconnected from the switch, then the switch isn't your problem.

The switch may of course be bad. Test with a multimeter and the wire disconnected: if the switch is grounded it's bad. In that case I'd just leave it disconnected: it's not really necessary IMO. If you lose fluid the light will light from the floats in the MC.

Tom

1963 Giulia Spider (1750 engine)
1974 GTV
1991 Spider
Former: 1987 Milano Gold
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