76 - C10 - Wiring upgrades/replacements/options

[Funstuie]

Hey all,

I've had my C10 for about 6 weeks and I am really enjoying driving it. But years of previous owners bodge jobs on the wiring has left it in a bit of mess.

So first up - the main functions work - it starts and drives without issue, the headlights and other exterior lights work.

Internally the dome light works, the floor light works occasionally, the cluster lights don't work. Someone has very crudely installed a JVC head unit (around 15 years ago) and although it works it can only pick up one station and has no connectivity options (Bluetooth, aux in, tape).

I finally got up under the dash and had a good look around. It's a rats nest. There are wires dangling everywhere, lots of ends not connected to anything. The original fuse box is still there with glass fuses and worryingly some wires just shoved in.

Also, there are two speakers behind the bench seat. they sound fine but the wires have just been run under the carpet.

So I would like to upgrade/clean up/replace the wiring in the cab (at least as a start). I have been looking at wiring harness' and it's a nightmare trying to work out what's what. Electrics are not really my thing. Also, I don't really have the option to take the truck off the road for an extended time. Would this be a project I could do over a weekend?

Finally in the current configuration (old fuse box etc) is there a way I could install a charge port so I can charge my phone?

I will post some pictures later of the current wiring for reference.

- 1976 C10, Stepside, shortbed, 5.7l V8, Auto.

[blindbug]

Originally Posted by Funstuie

Hey all,

I've had my C10 for about 6 weeks and I am really enjoying driving it. But years of previous owners bodge jobs on the wiring has left it in a bit of mess.

So first up - the main functions work - it starts and drives without issue, the headlights and other exterior lights work.

Internally the dome light works, the floor light works occasionally, the cluster lights don't work. Someone has very crudely installed a JVC head unit (around 15 years ago) and although it works it can only pick up one station and has no connectivity options (Bluetooth, aux in, tape).

I finally got up under the dash and had a good look around. It's a rats nest. There are wires dangling everywhere, lots of ends not connected to anything. The original fuse box is still there with glass fuses and worryingly some wires just shoved in.

Also, there are two speakers behind the bench seat. they sound fine but the wires have just been run under the carpet.

So I would like to upgrade/clean up/replace the wiring in the cab (at least as a start). I have been looking at wiring harness' and it's a nightmare trying to work out what's what. Electrics are not really my thing. Also, I don't really have the option to take the truck off the road for an extended time. Would this be a project I could do over a weekend?

Finally in the current configuration (old fuse box etc) is there a way I could install a charge port so I can charge my phone?

I will post some pictures later of the current wiring for reference.

- 1976 C10, Stepside, shortbed, 5.7l V8, Auto.

1. I don't know how much you are looking to invest, but if you REALLY want to re-do your wiring, you might talk to GMACHINZ (http://67-72chevytrucks.com/vboard/member.php?u=100343) here on the forum, he does impressive work at creating NEW 'new old stock' style harnesses in the correct colors and with the correct terminals and lengths. Pricing (I think) depends on what options you have installed and want to run.

2. The Dome light and under-the-dash courtesy light are pretty much independent of your gauge cluster. These lights are fed a constant positive from the battery (through the fuse box) and when you open your door, there is a little metal switch inside the door frame that extends out and gives your lights a ground and thus turning them on.

3. Your Head unit / CD Player is probably missing the Antenna wire. Look behind the deck and see if there is a wire going INTO the unit that looks like an all-metal RCA cable. It is more than likely going to come from the passenger side of behind the dash. You could have a front windshield antenna, in which case there is a little black piece that comes out where the dash meets the windshield right in the middle. If that black piece is not plugged into the window (I know it sounds odd) you wont get good reception. If you have an actual external antenna, then you might check that the wire is not clipped somewhere running from your head unit to the antenna. If it looks like it is, you can replace the antenna wire, or look at getting an aftermarket antenna setup.

4. "...and worryingly some wires just shoved in (to the fusebox)." This is the poor mans way of making a constant, or switched power supply to an add-on accessory. I suggest tracing these new wires from the fuse box to where they end. One will probably go towards your carburetor (assuming you have one with an electric choke) to tell the choke when to stop choking (lol). One, or more, will probably go to your CD player / Head Unit. If 2 go there, one is a constant and one is a switched. The constant keeps the head unit memory and clock running when you turn off your truck. The switched tells the head unit to turn on when you switch on your truck. One or more additional wires will go to various add-ons (battery voltage gauge, old CB radio installs, poorly added daytime running lights, etc.). Take it one wire at a time, figure out if the wire/accessory is needed anymore and remove it or terminate it correctly. If you have a lot of accessories, I suggest going to advance and getting a small fuse block, then running a wire directly from your battery to the new fuse block... or if it needs to be switched from the battery to a relay and then to the fuse block with the other terminal of the relay going to a switched position on the stock fuse block.

5. Speaker wire ran under the carpet is A-OK. If you really have an issue with it, just get some split loom and cover it up. Make sure you don't have any splices in between, just a continuous run from your head unit/amp directly to the speaker. When people splice 2 wires together it creates a lot of noise and issues.

6. For a charge port, go to advance and grab a cigarette lighter port and replace the one in your ash tray position... or mount it somewhere else if you want. Run a switched wire from your fuse panel to the back, and another wire from it to a ground. Easy install.

7. If some of your lights on your gauge cluster are not working, take out the cluster and clean the terminals, both on the cluster printed circuit and on the bulb sockets. The speedometer cable just clips on and there is a tab that you push back and the cable pops right out. If you have an oil pressure gauge, it might be manual and you have to unscrew it. The wires all plug in through a single connector. Take the cluster out, lay it face down on a towel (leave the plastic housing on the front)... take out each bulb holder by twisting counter-clockwise and then use some high grit sandpaper (800?) to sand down the terminals on the socket and bend them forward towards the bulb. Then do the same for the printed circuit on the back of the cluster. Be careful with the printed circuit as it is usually pretty brittle. I recommend going to eBay or Amazon and buying a cheap set of LED bulbs in size '168' to replace what is in your cluster well before you do this so you have them ready to install at the same time. When you do get the bulbs all back in, put the cluster back in its spot all connected, then take off the plastic front bezel and black bezel and turn your lights on with the switch to see if all the lights are working.... if you have idiot lights (just a light to say you have low oil pressure for instance instead of a gauge) then those particular lights are harder to test without triggering them and is much longer to detail.

Someone will come along shortly with the fuse diagram for your particular vehicle. It's posted somewhere on this forum, I can't seem to find it off hand.

What you will find in most cases is that someone didn't know what they were doing and just ran a new wire instead of using the wire that already existed and served its purpose has they just used it.

My main tip is to TAKE YOUR TIME. There is no reason to try to replace everything at once. Figure out what the previous owners have done, and have some paper ready to diagram where the wires are going and what they are there for (and whether they are constant, switched, accessory, etc.). Then, buy the right color of wire and replace them correctly. Terminate your ends with proper terminals (or as close as you can, some of these older terminals don't exist or are really expensive).

[blindbug]

Sorry for the novel.

[favor]

Good advice except make sure LED 168 bulbs are the type that will dim.If you cannot make them brighter or dimmer you may have trouble viewing at night.

[Funstuie]

Thanks for the advice.

[blindbug]

Originally Posted by Funstuie

Thanks for the advice.

No problem, one additional item I will add:

A lot of the issues you will find in these trucks relates to bad grounding. Either the old wires are corroded and not grounding properly, or the wire itself is toast. I was helping my brother diagnose a non-working dome light in his 82' k20 and found a wire that was 100% perfect from the outside, no knicks, no cuts, but when I tested continuity, there was a break in the wire INSIDE the plastic coating somewhere. We replaced the wire and boom it worked with no issues. For my truck, I ended up having to replace a bulb socket, which wasn't working and causing some funky acting lights working and not working and flashing when they shouldn't have been. The socket looked great, no corrosion (at least from the outside) but for some reason that was the culprit.

One additional item is that the gauge cluster, courtesy lights, and headlights all tie into the headlight switch next to your steering wheel. Sometimes this switch is the culprit. A replacement is less than $20, and a decent investment if you keep having issues even after everything else looks good.

I really suggest getting at least a continuity tester and some pigtails with alligator clips, which will go a long way to figuring out if power and/or a ground is getting from one end of the wire to another. Pick a spot where you would like to test your grounding, and make sure it gets a good ground by scuffing it up and testing against another spot on the frame.

Good luck!

[Jstock85]

Had similar issues. My only advice is to start small. Try bulbs and fuses and work into individual wire harnesses. Good luck!

[blindbug]

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

THERE'S the wiring diagrams I was looking for. Why was it so hard to find this post!

[andrewpclayton]

where is the "right" place to get power from for the electric choke?

[Palf70Step]

Fuse box has it's own connection for it, but you are looking for a switched on power source.

[blindbug]

Originally Posted by andrewpclayton

where is the "right" place to get power from for the electric choke?

That's a loaded question. The "right" place is to have a dedicated line coming from the battery to a relay which is triggered through a switched power source (ACC line from fusebox, usually). You can also get a switched line from the starter.

However, a generally proper way to use one of the ACC spots on your fusebox. There are proper end terminals for the 73-87 C10, but you can also use a spade terminal end that plugs into the fuse box. I WOULD NOT use a bare wire stuck into the fuse box.

It also depends on what you have installed on your fuse box. A fully optioned C10 isn't uncommon, but it isn't that common either... so there is usually a free ACC spot on the box, which is what I personally use for my electric choke. If all the spots are taken, you can get jumpers which add an a second fuse inline with the original, allowing you to add one additional, fused, line to an already existing connection.

[SunSoaked]

Originally Posted by blindbug

Sorry for the novel.

That was an awesome reply! I didn't even have an issue and still enjoyed reading it. I learn a lot from just reading the posts.

[Funstuie]

Quick update. I fixed the reception issue with the head unit. I pulled it out of the dash (it’s held in by friction and spit). There is two antenna cables back there. One goes to the dash/window but whatever it used to connect to is long gone. The other goes to the back of the cab. At some point someone fitted an antenna in the step well on the passenger side. I can only presume it was a whip antenna. Anyway there’s a hole in the cab but the antenna and mount are long gone. I went to orielly and got a side mount antenna. Hooked it up (there’s already holes for a mount) and I now have reception on the radio. It’s still a crap radio with no other connectivity option but at least I can listen to the radio. The speakers are not bad as it turns out.

[blindbug]

Originally Posted by SunSoaked

That was an awesome reply! I didn't even have an issue and still enjoyed reading it. I learn a lot from just reading the posts.

I like to help, when I can. Electrical is the one thing I'm good at. I'm slowly getting there with mechanical and engine work. I spent a good portion of my teen years + a decade or so wiring and re-wiring car stereos. At one point I had a company sponsored car and competed. Nothing super serious, but after so many cars and systems, you get a feel for it. Hell, when I bought my daily driver (an Altima :/ ) it had 15 miles on it when I took the head unit completely apart to try adding an RCA out. ended up fabbing a custom connector / adapter which worked for my needs.

Originally Posted by Funstuie

Quick update. I fixed the reception issue with the head unit. I pulled it out of the dash (it’s held in by friction and spit). There is two antenna cables back there. One goes to the dash/window but whatever it used to connect to is long gone. The other goes to the back of the cab. At some point someone fitted an antenna in the step well on the passenger side. I can only presume it was a whip antenna. Anyway there’s a hole in the cab but the antenna and mount are long gone. I went to orielly and got a side mount antenna. Hooked it up (there’s already holes for a mount) and I now have reception on the radio. It’s still a crap radio with no other connectivity option but at least I can listen to the radio. The speakers are not bad as it turns out.

Awesome, sometimes it's the little things that give you the extra umph to push you into completing another project and soon enough you're 'done' (pro tip: you are never done). I had a feeling it would be that antenna wire. There's no reason for a head unit to get some stations but not get others except for a bad antenna lead. If you look in the LMC catalog, you can find a new antenna adapter to replace the one that goes to your windshield... assuming you wanted to do that.