RABI
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Joined: Nov 2013
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RABI
1988 F150 4X4 5.8ltr C6
The abs lights up after I hit 41-42mph. The rear brake lights are dimly lit when I start her up in the mornings. I replaced the speed sensor and the abs hydraulic unit (rusted couldn't bleed\replace line).any ideas?
The abs lights up after I hit 41-42mph. The rear brake lights are dimly lit when I start her up in the mornings. I replaced the speed sensor and the abs hydraulic unit (rusted couldn't bleed\replace line).any ideas?
Senior User
Joined: Nov 2011
Posts: 456
Likes: 1
From: Owensboro, KY
If the brake lights are lit at all it'll cause a problem. The RABS module should click within a couple seconds if starting, and will not anytime the brake lights are on. If they are dimly lit, I'd bet on bad grounds and current flowing through them to ground to the brake lamp circuit. Check and clean your grounds, I'm betting the problem will go away. Only other thing I can think of is your brake light switch.
Laughing Gas
Joined: Nov 2013
Posts: 871
Likes: 6
From: Orcas Island, WA
I'd pick the brake switch. Bad grounds will cause some weird problems, but I don't think they'd cause the brake lights to be lit when the brake peddle isn't depressed. Either that, or a short between positive side of the brake light circuit and something else on the positive side of the battery.
Senior User
Joined: Nov 2011
Posts: 456
Likes: 1
From: Owensboro, KY
It seems odd doesn't it? I could be wrong but I had the same issue on my '95 Chevy, don't know if it would have the same effect on Fords. I don't have proof, so don't quote me, but I believe the RABS uses the brake lamp circuit to tell when the brakes are depressed and when it should be active. If the brake lamps are unplugged the RABS module won't function. Which also makes me realize, a faulty RABS module could be the culprit, sending voltage back through the brake lamp circuit when it isn't supposed to, hence them being dimly lit.
Laughing Gas
Joined: Nov 2013
Posts: 871
Likes: 6
From: Orcas Island, WA
Interesting premise. I could see it happening. I'm not familiar with the RABS setup, but it would take a pretty specific type of failure to cause this. Still, electronics can, and do, fail in mysterious ways. Is there a simple plug from the brake light circuit to the RABS? If so, unplugging the RABS would be a very simple test. Brake light out with RABS unplugged? If so, RABS defective. If not, RABS not the cause.
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Postmaster
Joined: Nov 2011
Posts: 3,533
Likes: 17
From: SW Florida
Sorry. I misread that post, I thought you meant the RABS warning light was dimly lit.
I would check the multifunction switch and trailer wiring/connector if you have it. These are the only places I can think of where voltage might be crossing over onto the brake light circuits.
Other than that, check the brake light switch itself. Might have just failed and is passing enough leakage current to dimly light the bulbs.
I would check the multifunction switch and trailer wiring/connector if you have it. These are the only places I can think of where voltage might be crossing over onto the brake light circuits.
Other than that, check the brake light switch itself. Might have just failed and is passing enough leakage current to dimly light the bulbs.
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