Desperately Need Help

[ChaseDale3and8]

I have owned my 86 K10 for the last 9 years or so and have never had any electrical problems with it .......until now. Trying to figure out WHAT and WHERE the problem is .....is just about to drive me nuts! I recently pulled the stock 305 out and put a built up 355 in it's place. I was extremely careful with the wiring harness during the engine change. I had it draped over the brake booster out of harm's way so nothing would pinch or otherwise damage it.

Once I got the 355 in, I wired up the engine and had it started, and it runs fine. So, since I already had the radiator support out anyway, I decided to change the grille from the original 2 headlight to a 4 headlight set up. I bought the correct harness, and plugged it in. Checked and made sure the lights worked, etc.  I finished up the wiring, plugging in the A/C, and everything else that was left, which wasn't much, just the passenger side headlights and the temp gauge.

Okay, at this point I hook the battery back up, and before I could react, the wire on the firewall block between the block and the fusible links got hot and melted in half! The next day, I looked the harness over really good and couldn't figure out what happened. Couldn't find a source of a short or anything. I went to O'Reilly and picked up a 30 amp fusible link, wired it in, and it promptly blew the fuse out. I looked the wiring over again, couldn't find anything wrong, and tried it again, which it promptly blew another fuse out.

At this point, I was done messing with it. I got in touch with a local guy that parts these old trucks out, and he happened to have another engine wiring harness. I just re-wired it up today, and it tried to do the same thing all over again when I started to hook up the positive battery cable!

I promptly disconnected it before it could melt the wire in the SAME EXACT SPOT between the block and the fusible link! So, I started disconnecting stuff to try and eliminate possibilities. When I disconnected the alternator and tried to hook the battery cable back up it didn't spark like it was trying to short out as it did before. Thinking that this alternator was bad, and possibly had the voltage regulator sticking, even though it's brand NEW, I removed it and bought another re-manufactured unit from O'Reilly.  I was happy....for about a minute thinking that I'd found the problem, and the solution.

Hooked it up, SAME PROBLEM! It's getting the wire between the block and the fusible link extremely hot, and if I were to leave it hooked up, it would either melt this wire as it did on the other harness, or I'd have an electrical fire! I UNHOOKED ALL the wires on the alternator though, and it doesn't act like something is shorting out! The gauges are all squirrelly and don't read where they should after I disconnect the alternator and turn the ignition switch on. I almost expected that though. The radio won't come on, and the fan won't work either.   

I'm not an electrician and I'm running out of ideas here. Not knowing what is connected to what, where, and why, doesn't help either. I just want to get this truck wired so that it runs, and everything that worked before will work again. The only other thing that even comes to mind is I put a new gear reduction starter on when I installed the 355. It's wired correctly, but could the solenoid be the source of this problem? I REALLY NEED HELP!!!!!!! I should have had this truck on the road a month ago, and here it still sits! THANKS IN ADVANCE GUYS!!!!!!!! ....Joe

[werewolfx13]

Rather than keep smoking a wire by hooking up the battery, use a multimeter or continuity tester to trace your short. I'm sure someone else with a diagram handy can tell you another way to trace your short, but if no one comes up with anything before you get itchy to do something, remove all your exterior bulbs..tail, front and rear turn, backup, side marker, headlights, everything. Next, start testing for continuity to the ground on all contacts of every socket. This should take about 10 minutes, and because your problem surfaced after changing your headlight harness, this is where I would start. Note every socket that shows continuity on all contact points, which ones show continuity on 2 out of 3 contacts (for the turn signals), and which ones show continuity on only one socket. See what this leads to.

[bd]

To avoid spending a fortune is fuse links, make up a ~2-ft long, 14-gauge test jumper with a couple of alligator clips at the ends and protect it with an inline 20-amp circuit breaker (see image).  When troubleshooting, insert the protected jumper between the power source and the load. 

IIR - Battery feeds 12-volt power via the large battery stud at the starter through a fusible link and 12-gauge wire to the firewall junction block.  From the junction block, battery power continues through a second fusible link and wire that runs directly to the firewall bulkhead connector and inside the cab to the ignition switch.  Other wires may connect to the junction block.  An additional fusible link off the starter battery stud feeds 12-volt power directly to the bulkhead connector and supplies the headlight switch and fuse block.

From your description, I assume that if you disconnect all the wires at the firewall junction block, nothing smokes.  So, with all the wires disconnected from the junction block, turn the headlamps on to see if they light.  Then turn the headlamps off and switch the ignition on.  Does the dash come to life?  This will verify the circuit description in the previous paragraph.  Next, switch the ignition off and reconnect the wires to the junction block one-at-a-time until the symptoms reappear (the breaker will pop).  This will at least tell you which wire to trace.  Inspect the harness as it passes over the brake booster and into the bulkhead.  From there, you may need to go into the cab and under the dash.  Hopefully, this will help you get rolling again.

[ChaseDale3and8]

Thanks for all the replies and help guys! I unhooked the alternator and put a new re-manufactured one on. Left it unhooked and tried to see if it would turn over, thinking that maybe the starter. The starter is a new mini starter that I bought from Skip White on eBay a while back. Worked fine when I started this engine on the stand, and once in the chassis after I installed it. When I turned the key, I heard it spinning, but the drive gear wouldn't kick in. I tried 3-4 times. Nothing. Put the stock starter on and she turns over now. I think I've narrowed it down to the single red wire that goes to the alternator now. When it isn't hooked up nothing happens. But if I hook it up, it sparks as soon as I try to hook up the positive cable. Does this help? Can't find anything wrong with the headlight harness. I even completely disconnected everything except the engine harness. Do those blocks on the firewall go bad? I have another one I can try. I'm not an electrician by any means, but I think I've got it narrowed down a little bit now. Where should I go from here? Thanks in advance for helping a dummy out! The mechanical stuff I can do, but the electrical really screws me up!  ....Joe

[bd]

Joe,
If you're smoking fusible links there must be a draw of 40+ amps.  That's a lot! 
To assist you as efficiently as possible, please post pics of the wire connections to the alternator including the regulator connections, the firewall junction block, and the starter.  Indicate which wire is getting hot/melting.

Some arcing at the battery is not unusual.  Make up a protected jumper as I suggested, previously, and insert that between the battery and battery cable.  If there's a "short" in the positive buss, the breaker will open instantly. 

If the breaker pops, then move the jumper in between the alternator and its charge lead.  If it still pops then the problem is with the alternator or the way it's connected.  How many wires connect to the alternator - 1 or 3?

The junction block is just 1 or 2 studs anchored in plastic.  If you think its cracked and shorting to ground, just unbolt it from the firewall so it hangs free and see what happens.  If it's broken, it will be obvious.

Electrical repair really isn't complicated, it's just abstract because you can't see it, which imparts a little bit of "mystery."

[ChaseDale3and8]

Found the problem today with the help of my next door neighbor when he came over this afternoon. It was so simple that I can't believe that I overlooked it so many times, and that I didn't catch it right off. I feel really stupid right now, but at least the problem is taken care of and should be good to go. I recently bought a brand new Ac/Delco battery since I was putting all new parts in throughout anyway. The old battery was 9 years old (surprised it lasted that long) and was beginning to get weak so I really needed a new one. Turns out that the posts were swapped to the opposite sides from the old battery to the new one. I was so used to the way that the old battery hooked up I inadvertently hooked the battery up THE WRONG WAY!!!!!! No wonder I was having so many problems all at once! My neighbor asked if it was reverse grounded today when he came over. I was thinking to myself, what a stupid question, of course not! When I asked him why he asked me that, he pointed out that I had the ground cable to the hot side of the battery! Right then, it all made perfect sense! I hooked everything back up the RIGHT way and started it right up without any more issues. This old truck was trying to tell me, but I just wasn't listening to what it was saying! Mystery solved, and THIS only goes to show to NEVER overlook the obvious! ......Joe

[bd]

...THIS only goes to show to NEVER overlook the obvious! ......Joe

Never a truer statement uttered!

[Tx_Phil]

Glad you found it.
Don't feel bad. I made a silly little problem into a big issue a couple of weeks ago. Want to have a little laugh? Give this post a read...

http://forum.73-87chevytrucks.com/smforum/index.php?topic=24599.msg205363#msg205363

[ChaseDale3and8]

It's amazing how such a simple thing can cause such complicated problems isn't it?! LOL I still feel really stupid especially since I burned up a perfectly good harness in the process, and then had to re-wire it with another one. It works now though so I'm happy! I might not have caught it yet if it hadn't been for my neighbor coming over. I was so used to the way the other battery was oriented with the posts the other way around, that I didn't even LOOK at the battery to make sure I was connecting it right!

I helped him out with his '47 Dodge street rod (powered by a 350 Chevy/TH 350) a few weeks back with a problem he was having so now we are even. His problem was he rebuilt his 600 Holley and he just couldn't seem to get running. Worse yet, he had gas all over the intake manifold. He thought that he had a bad gasket  that was causing it to leak like a sieve. I went over and took a look at it, and asked him where the transfer tube was that goes from the front to the back bowl. He says "right over here on the bench". I said "well that's your leak mystery right there"! He reinstalled it, and she still wouldn't start.

I checked and made sure there was power to the coil. Yep, we got power with the switch on. Pulled #1 plug out had him bump it over while I held a finger in #1 to bring #1 to TDC. Pulled the cap off to see where the rotor was pointed. It was 90* out. I pulled it, set it where it belongs, told him to give it a try, and it started right up! He had been fooling with this thing for months trying to get it to run! You couldn't pry that stupid grin off his face with a crowbar! I suppose that I'm about the same way now that he was then right about now! When you get to this level of frustration sometimes it just takes somebody else to come along and point out the obvious! ...Joe

[Tx_Phil]

When you get to this level of frustration sometimes it just takes somebody else to come along and point out the obvious! ...Joe

Boy you got that right.  I had convinced myself that something major was fried, maybe even the ECM.  It took a fresh set of eyes, a fresh mind, to talk me into going back and start with the basics.  It's silly how good you feel when all the sudden the problem is gone and things start working as they should.