C4 1990 Electrical Ccts FSM

Vettech · 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.

sirfixalot · 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.

Vettech · 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 · 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.

sirfixalot · 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.

Vettech · 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.

sirfixalot · May 20, 2021, 08:44:05 PM

I would have thought the glove box light would be orange & black

Vettech · 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 ?..

bfit · June 04, 2021, 06:10:58 PM

One would think nc to make the circuit to illuminate the light.
Si

Vettech · 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.

bfit · June 05, 2021, 09:49:38 AM

Someone said to me once that there only switches.
Bfit

Vettech · 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 · September 11, 2021, 03:04:24 PM

Any members out there with a GM 1990, 91 or 92 Electrical Diagnosis Service Manual Supplement, or if you have seen one for sale in Oz or could lend me. I have the 87 book, but as you all know the C4 Series 2 commenced in 90 and included a lot of changes esp in the electrical, electronics and dash/consol and wiring.

Please let me know, with warmer weather, I'm about to pull the RH seat out to find/fix these nagging irritating intermittent electrical faults. Untill found I suppose ill just have to be the passenger in the wifes Mustang. Of couse it also depends upon my latest bout of Gout in the right knee - which does tend to knobble ones movements, esp those requiring one to crawl head first upside down under the dash.

Vettech · September 12, 2021, 01:23:29 PM

OK a big thankyou once again to Uncle Burton (batee.com)
Always very helpfull.
He had some 90 circuit diagrams, see one attached.

My "security Indicator" is currently not working, and is one of several iritating minor electrical issues. I suppose we will start with the fuse and work our way to the globe. I'll get a pic of the "under dash" layout soon - this will give you an idea of the mess created by converters that us owners have to put up with.

Hopefully a wire, connector or splice, if its the bulb, then out comes the Instrument Cluster, and at this stage of disassembly it may just take four (4) more screws and it should unplug and pull out - of course once out, we may as well go over it and check everything.

Of course this is the simple side of the probable cause, the Central Control Module (CCM) switches this lamp on and off, and requires "X" number of inputs on its gates to give the desired response, so the search may become more involved.

sirfixalot · September 12, 2021, 08:23:51 PM

to check the fuse Doug just see what also is on same fuse. My first point to test after fuse would be to remove instrument cluster you then can test to prove + & - sides of circuit

Vettech · September 12, 2021, 10:54:30 PM

Yes I relented and removed the 4 x 7mm screws and pulled the instrument custer, but had to take front clear lens off before I could wiggle it out, since I could not find the bolts holding the steering up, which Youtubes say must be released to give the space.
Any way, there are twenty (20) mounted bulbs, cleaned and tested A-ok, also there is a bulb in the OD hole but it has blanking plastic piece blocking any light, the bulb is connected via copper traces on the PCB, so this answers my question from way back about the Over Drive light in the Series 2 C4's. G.M obviously thought it was too much of a distraction, so blanked it off.

I prefer the earlier flat digital IC, the colours are better and brighter, but as you can see this style is a complete unit, fully self contained and simply plugs into a captive socket in the rear of the cradle.

Alas i have not found the fault/s. Thanks Geoff, I now have several cct diags downloaded from Batee, but can't print as yet because "SHE" who currently works from home has used all the printer Ink, and we are in a bad Red Zone lockdown so are trapped.

Vettech · September 13, 2021, 03:28:14 PM

I don't believe I'm saying this, but 'B's company has directed her to "clear out her desk", but because we are in a "Red Zone" of contagion, she has had to apply to the NSW Gov't for a .......... wait for it........ a "Travel Permit" (home to city return) isnt that what we used to get along with "Smallpox" shots to go into less than savoury countries 50 years ago. We are both 2x AZ permit holders, whilst I believe in democracy and desease control - and yes they can easily co-exist, it appears that "Joh's Police State" is slowly moving south and taking hold.

Whilst the measures taken by the NSW Gov't are generally OK, there overall application and black & white dispensing leaves a lot to be desired. I appreciate that political statements are not wecome on the forum, but, enough is enough.

Recently a member on "H Plates" was told by RMS he could not re-register his car because they did not want him visiting their office, since people on "H Plates" must present a paper pink slip c/w other paperwork, "Their rule" as it cant be done electronically, he must wait till pandemic over. Now I dont know if that is a blanket across NSW rule, whether it was sorted by cooler heads or what, it would be good to see if any other members had the same issues.

I'll finish raving now since my blood pressure is thru the roof and to make matters worse its raining.

Vettech · September 17, 2021, 06:06:03 PM

Amazing the info out there, whilst my colour glossy 1990 sales brochure shows an OverDrive lamp on the Tacho half of the IP, I've found it is not there, the globe, wires pcb cct etc are, but the dial is not silk screened, and in a newly acquired GM technical training manual, covering the Central Control Module, a lamp layout diagram points to the spot and says "Vacant".

After reading, I now realise this CCM which they state is exclusive to the 1990 Corvette is the fore runner of the Body Control Module.

It does everything except the engine which is still done by the ECM.

This means things like VATS - passkey security, and doors, hatch, keys, AC, seatbelts, everything all feed one way or another via the CCM, and it it is all tracked, generates codes and can be diagnosed.

My new book covers how to get codes out, what they are and most important - how to reset them. This book is not the "be all end all" and is a handout to Qualified GM US Dealership Techs to upgrade them on the new features associated with the 1990 onwards.

So the Instrument panel is back together (with no left over parts), all checks out OK. NOW to get in and under the dash for the intermittent faults. I've some pics, which after they are schrinkted I'll post up. This was easy to pull apart, fairly straight forward, but i could not see any easy way to upgrade to LED without buying special led/globe fittings. The bulbs are a 161 and the globe is soldered and likely glued to the plastic base.

Vettech · September 19, 2021, 07:20:35 PM

I'll work on those pics, in the meantime, after being upside down head first under the RH dash, I can see where all the drivers AC air is going - straight out of the duct via 2" dia hole, not sure if this is a compromise from the LH~RH conversion, but the air basically floods the area under the dash, but with all pads and covers on, the air cant go anywhere but back into the return port, ergo bypassing the drivers vents completely. One glue job is being formulated.

Another thing I found was a relay hanging around doing ??, what is it for ??. With Pink, Orange, Black, Pink/ black stripe wires.
As dark set, I can't find its function, my limited 90 downloaded cct diags don't show it, neither do my 87 books, unplugging and trying everything from H'lights, Interior, fog, start, hatch, AC, parkers, etc etc..... maybe in the morrow and with a metre it could be the rear hatch de-fogger.

Vettech · September 20, 2021, 05:23:34 PM

Ok, after much ado, and confusion, we have three relays, two mounted on a plate, one has fat yellow wires and once pulled proved to be the "start" relay, whilst the one mounted next to it with 2 brown, Lt green, Grey wires proved via stephoscope to be the AC compressor relay. These wire colours are confirmed from the downloaded diagrams That still leaves the 3rd hanging relay, its black wire is earth whilst its Red is 12volts always.
No end of pressing buttons, or listening for a click can I determine what it does. I've a gut feeling its the fuel relay, and the car now cranks over several times before starting, and I'm probably going deaf, but I cant hear the fuel pump pressurise the fuel rail prior to cranking. With good Oil and Oil pump it is theoretically possible to start on the Oil Pressure Switch.... ummm .

This relay checks out OK. BUT I can't find a cct dia on the web.