Dome and Courtesy light issue

[Backfoot100]

Ok guys, been going over schematics and every thread about lights that I can find.

I have an 86 Sub and when the rear doors open both dome lights come on. Same when you open the rear cargo door.
Front doors open and turn on the courtesy light under the dash or if you manually turn it on rotating the light switch CCW. I know the dome and courtesy should all light when any door opens or the light switch is rotated CCW.

All other lights seem to be fine. Dash, dimmer, head lights, tail lights, turn signals, horn.

In looking at the schematics the courtesy light and dome are fed by two different fuses but they share the same ground path. I'm thinking there has to be a break someplace in that path between the front and rear doors.

This thing had new carpet installed before I bought it and Im thinking checking the threshold plate as a start.
Any other thoughts where I should look?

Thanks in advance.

 

[chengny]

Ok guys, been going over schematics and every thread about lights that I can find.

I have an 86 Sub and when the rear doors open both dome lights come on. Same when you open the rear cargo door.
Front doors open and turn on the courtesy light under the dash or if you manually turn it on rotating the light switch CCW. I know the dome and courtesy should all light when any door opens or the light switch is rotated CCW.

All other lights seem to be fine. Dash, dimmer, head lights, tail lights, turn signals, horn.

In looking at the schematics the courtesy light and dome are fed by two different fuses but they share the same ground path. I'm thinking there has to be a break someplace in that path between the front and rear doors.

This thing had new carpet installed before I bought it and Im thinking checking the threshold plate as a start.
Any other thoughts where I should look?

Thanks in advance.

Is this correct:

1. Both dome lights illuminate when rear doors or tailgate are opened - but no courtesy lighting

2. No dome lights (front or rear) when front doors are opened - or when the rheostat is fully rotated CCW.

3. Courtesy lighting will work when front doors are opened and by the rheostat


Appears that both domes have power, but no ground paths are created to them - by either the front door jamb switches or the rheostat. But ground paths are created by all three rear switches (L/R door jambs and tailgate).

Check connector C220A and make sure that the WHT leads on either side are securely connected. It may be that the forward ground paths for the dome lights (and the rear ground path for the courtesy lighting) are being lost at that point. The front grounds for the courtesy lighting are independent forward of the connector. The C220A connector is in the LH B pillar.

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[Backfoot100]

Hey Chengny,
You're the f*****g man!!!!!! I opened up the B pillar and immediately saw the issue. When the plug was pushed into the socket of C220A the ground pin pushed out the backside of the socket. Got it reseated as it should be and everything works as it should. We were both right on the diagnosis, I just had no clue where to start looking to solve the problem.

So now my next question is what manual did you get that wiring diagram and illustration????? I downloaded about everything I could find here but I found nothing like that unless I just missed it. I would love to get one of whatever that manual is.

Thanks so much your help.

Eddie

 

[chengny]

Hey Chengny,
You're the f*****g man!!!!!! I opened up the B pillar and immediately saw the issue. When the plug was pushed into the socket of C220A the ground pin pushed out the backside of the socket. Got it reseated as it should be and everything works as it should. We were both right on the diagnosis, I just had no clue where to start looking to solve the problem.

So now my next question is what manual did you get that wiring diagram and illustration????? I downloaded about everything I could find here but I found nothing like that unless I just missed it. I would love to get one of whatever that manual is.

Thanks so much your help.

Eddie

Those images were from the 1990 GM RV & P Light Truck Wiring Manual.

While 1987 was the last year of production for the C/K 10/20 line of trucks, GM continued using the pre-88 design features - including the electrical systems - for selected models (C/K 30, Suburban/Blazer and maybe 30 series crewcabs - I'm not sure on that). So whenever possible, when posting electrical related images, I use the wiring manuals for the later models. That's mainly because the wiring diagrams are way clearer. But it is also because the circuits are presented individually and component locations - as well as diagnostic procedures for the various systems - are included.

Hit the link below and you will find a goldmine of easily downloadable - and free - Square Body reference material. And let's not forget who put in all the hours of hard work required to make this vast library of data available (even though it was posted on a rival forum - jk). It was all done by another GMSB forum member from NH - @hatzie.

Thank you from all of us Mr. hatzie (LFOD)!



http://67-72chevytrucks.com/vboard/showthread.php?t=545416

 

[hatzie]

The harness layouts are shown in the 90 & 91 wiring manuals. Despite the many changes over the years, the layouts GM used on the last two years of the squares provide a reasonable place to start looking for the components... if not exactly where they were placed.
I'm a member of several squarebody related forums. Good folks on all of them. No need to be stingy with the scans. They're in the forum library or just open the links in my signature.

I would recommend acquiring the paper manuals for your year if you can find em. The 70's along with the early and late 80's seem to be more available than the mid 84 & 85 manuals for some reason. None are super expensive like the 2001 GMT800 Service and Transmission Unit Repair manuals I bought recently. You can find all three or four volumes of the square service lit for less than $100. Look at the prices on the T400 T800 & T900 manuals but sit down first... $350 for my NEW 2001 T800 full set and that was a good deal. Look at the Helm prices on the newer rigs manuals if you want a real wakeup call.

 

[Backfoot100]

Thanks guys.
I did download the manuals for 81-87 but they're not like the 90 manual like Chengny said. Never would've thought to try looking at another year manual. I have that downloaded too. I'll be doing some searching to try and find hard copies of them

I certainly echo Chengny about Hatzie's effort too.
Thank you so much.