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C4 1990 Electrical Ccts FSM

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Vettech:
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:
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:
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:
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:
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.

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