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Looking for help on my ABS wiring. After resurrecting my 90 convertible and finishing ALL the mechanical stuff. I was getting close to test start it. I was installing the last "part" new carpet so the carpet was removed. Lo and behold I find a burnt wire in the harness. Turned out to be the ABS harness ground wire.Pull out my FSM and trace out the circuit..The ground for the solenoid valve relay on the modulator valve has completely burnt from one end to the other. The car drove and ran fine with no "service ABS " lite when I parked it 12 years ago. The battery was removed at that time. This problem could have been there for a long time.
At the ABS harness connector terminal #8 wire #150 (Ground). Looks like this circuit has something to do with the service ABS indicator. There is a diode in parallel with that light circuit from EBCM terminal #29 (service ABS indicator control) down to terminal #4 on the modulator valve. It goes through Common terminal #30 (COM) at the solenoid valve relay through normal closed (NC) contact #87a and back to ground. I am not understanding the purpose of this circuit , I have concluded it has something to do with the ABS light coming "ON" during initial start up. I have tested the relay, traced and check ALL the wiring in that harness. I have it on my bench. I am thinking it can't be a dead short the fuse should pop. All the relays "so far" have checked out OK. So why a burnt ground? Overload on the circuit? Faulty ground somewhere else? I am going to check the ground termination behind the pass. seat next. Possible return pump motor ground issue? Looking for some direction what to check next ? And what is the purpose of that circuit?
Thanks for your help
Regards
Mike
If the ABS Diode is shorted or installed backwards it would burn up that ground wire if the solenoid valve relay is energized. Make sure the cluster fuse is actually 5 amps as that should protect that ground wire.
Last edited by JimLentz; Jun 19, 2018 at 02:58 PM.
I was thinking the diode might be installed backwards too or failed . Not sure how to check that. Google is your friend! Thanks for the heads up.
Mike
Diode installed correctly and functioning at .568 VDC volt drop. According to my 6 minutes of you tube education. I am installing a new wire high temp insulation and increase from #16AWG to #14 AWG.. I a thinking I should run that new ground wire on the outside of the plastic loom. The original melt down did cause some very minor collateral damage. Would be easier to monitor any over heating or easier to burnt the car down! Not sure which one would come first.
Just make sure that the solenoid valve relay is wired correctly and the right part. If pins 87 and 87a were ever connected it would burn up the ground wire as pin 87 goes through a fusible link to the battery and 87a goes to that ground wire. That is the only other failure mode I see for this circuit.
I am going to check that. Thank you.
Going back together now. I will Test all circuit before buttoning down the carpet and panels.Both static and live. I will see what happens.
Looks like I found the source of the burnt wiring. After re-building the Harness I was testing ,checking, cleaning all the connectors and LO and Behold what is that under the ABS solenoid connector?? Looks like the assembly line worker using the pop rivet gun let one of the stems get away. Look were it landed. Now the big question is is the ABS module fried? I won't know until i power it. Now I am beginning to wonder if the ABS ever worked from day one?Having the circuit for the ABS fault lite failed it is possible. I have been trying to think about any ABS activation in a quick stop situation since I have own the car. I don't recall any pulsation of the brake system in a quick stop mode. Hard to remember after 25 years of owner ship. If the stem stayed in that exact position all these years it looks like only one pin grounded out. So how the heck did it get out of the factory like that? I think GM owes me some warranty!
Looks like I found the source of the burnt wiring. After re-building the Harness I was testing ,checking, cleaning all the connectors and LO and Behold what is that under the ABS solenoid connector?? Looks like the assembly line worker using the pop rivet gun let one of the stems get away. Look were it landed. Now the big question is is the ABS module fried? I won't know until i power it. Now I am beginning to wonder if the ABS ever worked from day one?Having the circuit for the ABS fault lite failed it is possible. I have been trying to think about any ABS activation in a quick stop situation since I have own the car. I don't recall any pulsation of the brake system in a quick stop mode. Hard to remember after 25 years of owner ship. If the stem stayed in that exact position all these years it looks like only one pin grounded out. So how the heck did it get out of the factory like that? I think GM owes me some warranty!
WOW!!. Glad you found it. Good thing there wasn't further damage!
I haven't powered it up yet. Looking at doing that tonight. I think I am going to find a failed fusible link. The terminal the stem is grounding is #12 which is the power supply to the solenoid relay. I am crossing my fingers, hoping nothing else is fried.
Mike
ABS wiring burnt
