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Why so hard to find wiring diagrams for GM cars?


JensenHealey
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So I normally work on various European cars and it has been my experience that finding good wiring diagrams for european cars is MUCH easier than finding wiring diagrams for american (GM) cars. For instance I can find complete wiring diagrams for the 1988 - 1994 Jaguar XJ6 cars or the 1995 - 1997 Jaguar XJ6 cars that I do a lot of work on. Or for the 1985 - 1989 Merkur XR4Ti or 1988 - 1990 Lotus Esprit cars I also work on. But for the last few days I have been trying to locate wiring diagrams for the 1989 Chevy Caprice that I believe my 1989 Avanti convertible is built on. But so far my search has not turned up any information. I had this same problem years ago when I first purchased my 1986 Chevy K30 pickup truck. Nearly impossible to find good General Motors car or truck wiring diagrams.

Does anyone have a suggestion where I can find good detailed accurate wiring diagrams that would help me work on the 1989 Caprice based Avanti and the 1988 Monte Carlo based Avanti cars?

Thanks in advance

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The Chevrolet based Avanti used part of the Chevrolet harness and part of the Avanti harness wired together. I have access to both Chevrolet wiring diagrams and the 1987 Avanti wiring diagram.

What are you needing?

You can also order the Chevrolet Service Manual for your K30, it will have the wiring diagram in it.

https://www.factoryrepairmanuals.com/search.php?search_query="ST33086-GU"%2C"ST33386VG"%2C"ST33086WDG"%2C"ST33086-RP"&ymmq=yr_1986~mk_chevrolet~th_k20&section=product

Just remember that US made cars use Angry Pixies and Magic Smoke in their wiring diagrams.

Good luck,

Jim Wood

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I agree with Jim above. That's why I always bought the factory manuals when I purchased a "New" daily driver. They finally priced me out of the market but the local library usually had up to date Mitchell's Manuals that had what I needed. Pretty hard to get to them now however, and my guess is they will not be digitizing them and will probably, if they have not done it by now, be purging them.

That leaves the link that Jim posted.

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3 hours ago, Avanti83 said:

I agree with Jim above. That's why I always bought the factory manuals when I purchased a "New" daily driver. They finally priced me out of the market but the local library usually had up to date Mitchell's Manuals that had what I needed. Pretty hard to get to them now however, and my guess is they will not be digitizing them and will probably, if they have not done it by now, be purging them.

That leaves the link that Jim posted.

I have my garage signed up to Alldata, I can get pretty much any factory wiring diagram, US or foreign. If Alldata doesn't have them on-line I can get them from their library. I needed a wiring diagram for a 1942 Plymonth about a year ago, they faxed it right over.

Good luck,

Jim Wood

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Right now I am specifically looking for the connector pinout for the electrical connection going to the fuel tank and the location & pinout for the fuel pump relay but I would also like to figure out why my headlights and taillights do not function. Later I would like to dig into the harness for the TBI system

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My point is I can go to a web site managed by the Jaguar enthusiast community and download for FREE complete pdf copies of the wiring diagrams for pretty much any classic Jaguar. I can do the same for other european marks that I typically work on. Why is this not possible for GM made vehicles?

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2 hours ago, JensenHealey said:

My point is I can go to a web site managed by the Jaguar enthusiast community and download for FREE complete pdf copies of the wiring diagrams for pretty much any classic Jaguar. I can do the same for other european marks that I typically work on. Why is this not possible for GM made vehicles?

Factory diagrams are copyrighted. European makes must not care if you use their materials.

2 hours ago, JensenHealey said:

Right now I am specifically looking for the connector pinout for the electrical connection going to the fuel tank and the location & pinout for the fuel pump relay but I would also like to figure out why my headlights and taillights do not function. Later I would like to dig into the harness for the TBI system

Pinout for which year Avanti? Both fuel pump and TBI could be GM vehicle specific.

Bosch style relay, will have diagram on relay. God only knows where Avanti placed it.

Lights are part of the Avanti harness on my 1987 Avanti. I have the 1987 diagrams, don’t know if they are the same.

Let me know what you need and I will try to get it.

Good luck,

Jim Wood

 

 

 

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Posted (edited)

Why not post any available Avanti diagrams here on this forum as a member resource?

It's not like anyone from Avanti is out there looking to take people to court for posting such material.

Edited by JensenHealey
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19 hours ago, JensenHealey said:

Why not post any available Avanti diagrams here on this forum as a member resource?

It's not like anyone from Avanti is out there looking to take people to court for posting such material.

I find it interesting that you assume it hasn't been done in the past.

I have also offered you the diagrams that you want for free, even through it costs me.

Don't know what else can be done.

Good luck,

Jim Wood

 

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I bought a GM manual that is supposed to cover 1989 GM CARLINE B SERVICE MANUAL ST-329-89 CAPRICE SAFARI LESABRE CUSTOM CRUISER off ebay and the seller says it has wiring diagrams in it. Hopefully this will help with the fuel system and engine management stuff.

But I spoke with a knowledgeable former Avanti employee and he tells me that only part of the car's wiring harness is from the Caprice. He said parts of the body harness is a custom Avanti harness. So my hope of using the Caprice manual to help with the no power to headlights, taillights, and dash lights is probably not going to work out since those parts of the electrical system are probably not covered it the GM manual.

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19 hours ago, JensenHealey said:

I bought a GM manual that is supposed to cover 1989 GM CARLINE B SERVICE MANUAL ST-329-89 CAPRICE SAFARI LESABRE CUSTOM CRUISER off ebay and the seller says it has wiring diagrams in it. Hopefully this will help with the fuel system and engine management stuff.

But I spoke with a knowledgeable former Avanti employee and he tells me that only part of the car's wiring harness is from the Caprice. He said parts of the body harness is a custom Avanti harness. So my hope of using the Caprice manual to help with the no power to headlights, taillights, and dash lights is probably not going to work out since those parts of the electrical system are probably not covered it the GM manual.

Yup! I suspect you have now discovered why a couple of the best tools for old cars is a Volt-Ohm-Meter and a 12 volt probe. Even with a complete wiring diagram (if available) you will still need to generally start at either the fuse box or affected end and start back tracking. Avanti's are well known for corrosion and bad grounds causing issues.

I would suspect your manual (if available) should list the fuses that feed certain parts. If not, the 12 v probe will make sure there is power to all the fuses whether on full time, or in run or start mode.

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My 87 Coupe has 3 wires supplying power to the fuse block, sounds like one of them is dead. Check at the firewall plug connector, for power on both sides.

Good luck,

Jim Wood

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On 1/10/2021 at 12:37 PM, Avanti83 said:

Yup! I suspect you have now discovered why a couple of the best tools for old cars is a Volt-Ohm-Meter and a 12 volt probe. Even with a complete wiring diagram (if available) you will still need to generally start at either the fuse box or affected end and start back tracking. Avanti's are well known for corrosion and bad grounds causing issues.

I would suspect your manual (if available) should list the fuses that feed certain parts. If not, the 12 v probe will make sure there is power to all the fuses whether on full time, or in run or start mode.

I highly recommend a Power Probe for testing car electrical.

https://www.amazon.com/Power-Probe-III-Clamshell-Automotive/dp/B00G4YUWMC/ref=sr_1_7?dchild=1&hvadid=77859221684039&hvbmt=be&hvdev=c&hvqmt=e&keywords=power+probe&qid=1610479502&sr=8-7&tag=mh0b-20

Can save a lot of time and headaches. You can test for power and grounds and supply both power and ground. Great for testing circuits or an electrical device, especially on a fiberglass vehicle.

Good luck,

Jim Wood

 

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