Author Topic: C4 1990 Electrical Ccts FSM  (Read 332 times)

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Offline Vettech

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C4 1990 Electrical Ccts FSM
« on: May 15, 2021, 11:34:15 AM »
Any one out there with GMFSM Electrical Supplement for 1990 Vett.

I have several (2) plugs floating under the centre console.
1. A black 2 pin plug c/w a black wire & black/white stripe wire.
2. A black 8 pin oblong plug c/w six wires only. 

The 2nd plug has a mounting pin, I think its safe to assume this has a module with flying lead that plugs into it, thence its mounting pin is snapped into a retaining hole in the console hardware. The wires then run forward into/under the dash centre instruments, there are no unplugged modules ??. The only optionable module fitted in this area is the switch for FX3.  But this option would at a guess require no more than four (4) wires which should run back into the ABS box behind the LH seat. There are no FX3 shocks, actuators, harnesses, controller's or console switches fitted to vehicle. These plugs are not present on my 87. Any ideas muchly appreciated.

I have a 1990 cct diagram which equates to my 87 book as 8A - 20 - 2 but its in conjunction with page 3, but I cant find anywhere a copy of the 1990 page 3/or second half of the working ccts for Automatic transmission - any help here would be great.

Vettech.

Offline sirfixalot

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Re: C4 1990 Electrical Ccts FSM
« Reply #1 on: May 15, 2021, 01:03:33 PM »
Doug I would reckon the black pair is for seat belt warning light /alarm normally drivers side stalk has a switch incorporated into the head of stalk.

Offline Vettech

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Re: C4 1990 Electrical Ccts FSM
« Reply #2 on: May 15, 2021, 06:51:27 PM »
Ummm thats not a bad suggestion Geoff.

I know I looked - there is two wires going down to my RH drivers seat, they disappear down behind the console side cover.
Maybe - its an option for the original passenger seat (RH side)

I think one is earth, but with ignition on, the blk/wht has power on it. Ummm something to follow up tomorrow depending on how deep the snow is. Its cold out there now.

Vettech.

Offline Vettech

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Re: C4 1990 Electrical Ccts FSM
« Reply #3 on: May 18, 2021, 07:56:04 PM »
The belt stalks look like early Holden Comodore without any wires attatched to either.

So I tink your suggestion "its the seat belt alarm" is correct.

This car has no seat belt alarms I can see - plus I've now made the mistake of pursuing structual issues in the console and the centre console plate and its equip alignment etc. I should have left well enough alone.


Vettech.

Offline sirfixalot

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Re: C4 1990 Electrical Ccts FSM
« Reply #4 on: May 19, 2021, 01:42:09 PM »
I can get the stalk with a switch in it seat belt light should stay on when car started for about 10 seconds. The switch in stalk is another parallel path until seat belt buckle is engaged then light goes out.

Offline Vettech

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Re: C4 1990 Electrical Ccts FSM
« Reply #5 on: May 19, 2021, 08:03:46 PM »
Those two wires, I thought were for seat belt - pretty sure they go down around into the centre glove box, it has a mercury switch and lights when glove box lid is opened. I gave the light switch a clean and painted white the surfaces behind the globe (T5) and the green LED indicator for Fog Lamps on.

Both are now much brighter, great at night, but I can actually see the led now in the daylight. Found the main Instrument shroud had been previously repaired and re- cracked - so the glue is setting. Love Corvettes.
Vettech.

Offline sirfixalot

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Re: C4 1990 Electrical Ccts FSM
« Reply #6 on: May 20, 2021, 08:44:05 PM »
I would have thought the glove box light would be orange & black

Offline Vettech

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Re: C4 1990 Electrical Ccts FSM
« Reply #7 on: June 04, 2021, 03:07:00 PM »
Quick question - I'm not near my books - the seat belt switch is what ? NC or NO when the belt NOT inserted ?..

Vettech.

Offline Bfit

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Re: C4 1990 Electrical Ccts FSM
« Reply #8 on: June 04, 2021, 06:10:58 PM »
One would think nc to make the circuit to illuminate the light.
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Offline Vettech

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Re: C4 1990 Electrical Ccts FSM
« Reply #9 on: June 04, 2021, 08:23:51 PM »
This is a C4 complete with electronics Bfit, between the belt switch and light there is most likely a motza of electronical bibs and bobs.
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Offline Bfit

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Re: C4 1990 Electrical Ccts FSM
« Reply #10 on: June 05, 2021, 09:49:38 AM »
Someone said to me once that there only switches.
Bfit
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Offline Vettech

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Re: C4 1990 Electrical Ccts FSM
« Reply #11 on: June 05, 2021, 11:15:25 AM »
Yes well said Bfit, there is nothing like "Boolean Logic".
Which is like getting thru a Gate or two or is it like jumping thru hoops?

Needless to say I'm home now, and referring to the Gospel according to GM - it shows that the seat belt switch is an "NC" contactor.
Supplies earth to the Audio Alarm Module's A2 input (C4 84~89). A quick glance at the cct below shows that AAM then switches or flashes the "Fasten Seatbelt Lamp".

Once belt is buckled, the cct is opened and removes the earth from the "A2" input. Which now answers another question, the loose plug in the centre console, its open cct, ergo no seat belt alarms, since I need to get under LH footwell to restore relays & fittings etc back to normal, I'll remove the seat for ease and double check the seat belt fitting to ensure there is no switch.



Vettech.