'79 GMC Restoration Help needed


Junior Member
My friend who I used to mow lawns with, folded his business
and gave me his GMC pickup for free. It's in rough shape.
I got it started with only recharging the battery and fired right up, replaced a brake line and it's mobile now, but far from getting through inspection and registered.
Don't know too much about Chevy/GMC trucks but have basic
mechanical knowledge. Where do I start? Is there some good books I could read up on Chevy/GMC pickup restoration?
I am looking for lots of detailed info. Chilton book from
my local library is just too brief.
I want to restore this truck and learn about restoration.
vin #TKL1491523401, "15 Royal Sierra" Is this model a C or K ....or are those only for Chevy trucks? has a Meyers plow, 4x4 full time NP203 Xcase,350 auto,1/2ton,8'bed
I need a wiring diagram for the electrical, head lights don't work, tried new lamps, no voltage at the sockets
Can I replace the front drive with a 205 Xcase and locking hubs? This truck needs alot of body work and everything is rusted on the frame and all metal fuild lines are in bad shape.


2000 Club Member
You might try the diesel page.com they are into all types of chevy/gmc trucks they could probaly tell you where to get the right info that your looking for or mayby look up the plowking Dino in here.As far as the C & K C stands for two wheel drive and the K stands for 4 wheel drive.


2000 Club Member
Oh one other thing look to see how much you will have to put into this thing before you start to restore it .You might be better off to just get a newer truck that need less repair.Sometimes even for free it isn't worth the time and money you will have to spent to get in up to good operating condition.Just a thought becuse i went thru the same type of deal and found other thing start to go as i finished with the other and went thru mega $$ in the process.


Senior Member
Sounds just like me last fall..........
Bought a 79 shortbed Chevy with a Boss V-plow for $1000.
The plow was worth more than that. But I kept the truck, & good thing I did, cuz my other one broke down & that rust bucket 79 plowed all winter for me! Lots of answered prayers there.
C is for 2wd, K or V is 4wd. Mine has the worthless 203 also; can't even do donuts with it :(
Brake lines were all rusty, bed was held by 2 bolts, etc.etc.etc. A real POS. Anyway I found a place in my heart for it & my dad bought it & plans to fix it up a little.
Frame almost broke in 2 before I welded it back into shape at work last fall, also. These are worth limping along $$ wise enuf to keep them safe, but there's so many out there that are better prospects for resto work. I'd keep it for a backup or wood hauler.
I tried but had a real hard time trying to get it stuck with that 203 'case & no bed! Thing won't die!

Chuck Smith

2000 Club Member
73 - 87 Restoration Help

Welcome to the Forum Daniel. I can break down your VIN # for you.
It's all on my web site, (www.chuckschevytruckpages.com)
but I'll break it down for you here.

TKL1491 523401

T = GMC (C = Chevrolet)
K = 4wd chassis (C = 2wd)
L = 350 V 8 motor
1 = 1/2 Ton series
4 = pick up (3 = cab and chassis)
9 = 1979 Model Year
1 = Assembly plant GM of Canada Oshawa

423,400th truck built at that plant that year (they start with 100,001)

Ok, I guess I might be alone in my opinion. I can explain. If you were to put money into this truck, you could basically have a "new" truck. Let's be extreme. Say you put $7,000 into it. Do you have any idea how much you can do to a 1979 GM truck with that much money? Provided you do the work yourself, the money goes far. VERY far.

Parts are plentiful, and cheap compared to newer trucks, and other makes. The most useful book you can get is a GM factory service manual. IT has EVERYTHING you want to know. There is a seperate one with wiring diagrams in it. The factory service manual does have some diagrams, of some circuits though.

As far as the NP 203 fulltime 4wd transfer case, it's a beast, and VERY strong. It's rated at 10,000 lbs. GVWR. Not bad considering it's in a 1/2 ton truck. It's a cast iron case, not aluminum like newer trucks. Aside from replacing the chain inside, there's not much more it needs. The chain is about $150. A kit to convert it to part time 4wd is less than $200. Then you'll have locking hubs on the front axle. Changing to a NP 205 is nice, but those cases are getting expensive. Also you'd need an adapter to use it in place of the NP 203. You'd also need a new driveshaft, or one from the truck you got the NP 205 from.
Interestingly, when you convert the case to part time 4wd, you gain an extra gear. The old 4 hi position, becomes 2wd hi. The old 4wd lo position becomes 2wd LO. The old 4 Hi Loc
becomes 4wd hi, and the old 4wd Lo Loc becomes 4wd low.
The 2wd Lo coms in handy for backing trailers up steep boat ramps, or a loaded landscape trailer up a steep driveway.

The rear axle in your truck I believe is a GM 12 bolt. It's a strong axle, not the strongest, but not weak either. It's the GM 10 you have to look out for. It's weak compared to the 12 bolt, and GM 14 bolt.

The body, well, it's rusty I'm sure. THe parts are easy to replace, and readily available. THe cab floor, and rocker panels you'll need a MIG welder to replace. Other than those, everything bolts on. Even the bed is bolted together. About 100 bolts. The beds are the same on 73 - 87 trucks, both GMC and Chevy, both 2wd and 4wd. The hood and fenders are the same on 73 - 80 trucks 2wd, and 4wd, Chevy and GMC. The doors are the same from 77 - 87. The front grille is all that changed during those time frames as far as the nose goes.

It is a good idea to change all the steel lines like you said. It's more time consuming, and torn knuckles than costly. You want to change all the brake lines, including the flex lines out to the front wheels. They go bad internally, even though they look fine on the outside. When you do them, you may need new calipers, and wheel cylinders. The reason is the bleeder valves may be rusted shut. So even if you get the lines out without damage, you might not be ableto bleed the brakes when you are done. Also, when trying to get the brake lines out of them, the lines sometimes want to twist. It's much easier to replace the lines, cyliners, and calipers at the same time.

Replace the fuel lines from the tank to the fuel pump. Be sure to replace the small sections of flex lines too. Add an inline fuel filter while you're at it.

There's another steel line that goes down to the trans module. It's usually ok, because of grease oil and grime on it. At the end of it, right at the module, is a piece of vacuum hose, replace it. Replace all the vacuum lines under the hood too.

As far as the lights go, first clean all the ground connections. I know you said you have no power, but clean all the grounds. Remove the tail lights, and clean the grounds for them on the body. That way you know all your light grounds are good.

The most common cause of headlight trouble on your 79 is the dimmer switch on the floor for the high beams. Rust is the culprit usually. Use a test light at the dimmer switch. If there is only power to the light blue wire there, replace the dimmer switch.

Of course, first you want to make sure you have power at the fuse box for the headlight circuit. Use a test light, and test both sides of the fuse.

To test the headlight switch, use the test light again. If there is power at the red & white wire at the headlight switch, but no power at the light blue wire at the headlight switch, replace the headlight switch.

If there is no power at the red wire, then there's a burned fusable link. This can be hard to locate. If this is the case. I'll look for it on my 80 GMC and help you along.

Well, I gave you an earfull, and can go on for days about these trucks. That's why I made my web site :)


mike reeh

Senior Member
Agreed. Convert the 203 case to part time.. Cheaper/easier than getting a used 205/adapter/driveshaft where u dont know how well it will work..

I will never run the 205.. if you ever shift a 205 case, then shift a 203 case, you will see that the 203 shifts SO much better.. and yes, having 2lo, 2hi, 4lo, 4hi is really awesome.. Even though I am partial to full time :/

Good luck..

mike reeh

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