no power to cab 68 GMC pickup

[welding83]

hey guys im a new member and this is my first post. i recently inherited my dads 1968 GMC pickup it has what i believe is the 250 inline 6 everything is original except for a few new parts put on this year to get it running. My dad had the truck since his early 20's took my mom on there first date brought me home from the hospital took me on my first camping trip etc. i would love to get this truck running and derivable. a few weeks agoi was heading home i started it up on a cold night once it had warmed up i pulled out the knob to turn on the headlights and the engine and every thing electrical shut off. ive replaced battery, voltage reg., and alternator im out of ideas please help!

[low&slow]

I had the same exact thing happen to me. I asked a ton of questions on this forum and even went to local auto repair shops and know one could figure it out. I was told there is a fuseable link near the starter, that if goes bad will cut power, but mine didn't have one. After hours on end of research and asking around and looking at all my wires, I decided to pull the fuse block to have it inspected. Although the fuse block had all new fuses, the fuse block itself was fried.

May not be your case, but find that fuseable link in the engine bay and check your fuse block. Also, check your fuses. Look for any brittle wires that may have corroded inside or cracked and is causing a short

[Hubscrub]

type in the search, (colored wiring diagram finished) there is some diagrams in that thread. I can't copy and paste on this thing. study it over and start tracking from the power back using a test light. Hope it helps

[welding83]

thanks for the help ive checked fuses under the dash and replaced all inline fuses under the hood ill check for a fuseable link but im thinking at this point with everything being original and my plans to restore the truck it might be worth the money to buy an updated wiring harness with a new fuse block that excepts the spade fuses. i had previously downloaded the colored wiring diagrams in hopes that i could trace the issue but no such luck ill let yall know what i find out

[low&slow]

A new wiring harness is always a nice way to go. Less headache when replacing other eltrical parts knowing all your wires are good. Here's a site I saved for a wiring harness that multiple people on this forum have used:

http://www.americanautowire.com/view...wiring-system/

If you do although figure it out, congrats and post what was wrong.

As mentioned above, a test light is an awesome idea.

[Redline novdog]

had this happen to me. Dead stick! hopefully u have a fusible link other wize y=the fuse block is fried. The fuseable link on mine you couldn't even tell it was cooked. Voltage tester verified. replaced the link with (fuseable link) haven't had a problem since. I have no idea what tripped it either. Sounds like a very special truck. Post up some pics!!!

[welding83]

Originally Posted by Redline novdog

had this happen to me. Dead stick! hopefully u have a fusible link other wize y=the fuse block is fried. The fuseable link on mine you couldn't even tell it was cooked. Voltage tester verified. replaced the link with (fuseable link) haven't had a problem since. I have no idea what tripped it either. Sounds like a very special truck. Post up some pics!!!

where did you find your fuseable link

[welding83]

it is special but at the moment its a pain i plan on rebuilding the stock motor so ill be taking it to a machine shop to have it bored it has almost 400,000 miles on it with everything being bone stock aside from sending unit and fuel pump that i replaced after it had been sitting for years

[Redline novdog]

mine was by the battery if memory is correct. Positive side of cables just beside the radiator.

[Redline novdog]

If you can se it ,was the blue wire going to the junction block on the right hand fender by the battery.You sparked my interest, but it is way cold out there for an old guy! HA! Hope it helps and good luck! Post some Pics !!! sounds like an awesome truck!

[franken]

You should get a voltmeter (DVM), and begin by measuring across the battery terminals.
Next verify you get the same voltage from the + terminal to the body.
Then start working your way to the bulkhead connector.

[welding83]

i appreciate the picture and links ill work on getting some pictures tomorrow before going in to a food coma and post them. the battery is brand new i just had it swapped out last week i was told the old battery had gone bad but it too had just been purchased a month or two ago

[67 chevelle]

check your ignition switch , could cause this issue

[low&slow]

67 chevelle may be on to something. Never thought of that one only because I'm running switches and a push start button. But I don't see how a headlight switch could make the ignition go bad, but its worth looking at since you want to restore the truck

[midniteblues]

check the main power wire going into the bulkhead ive had that connector corrode in the bulkhead and cause problems.

I had power everywhere under the hood and nothing in or going out of the cab.

had power up too the bulkhead but nothing on the otherside at the fuseblock.

wiggled jiggled that dang wire and notheing.
finally disconnected the bulkhead from the firewall dug out some of the tar like sealer and pulled the connector outa the plastic guess what the spade connector came out in two peices.

even though i wiggled and jiggled it wouldnt come out and it felt solid but i knew there was a problem with with it.

I had this happen on two trucks

[welding83]

ill try and get some pictures up

[welding83]

here is a look under the hood

[welding83]

..

[welding83]

idk why it fliped that last photo

[Koffer]

Very nice looking GMC .
A good test light is a nice inexpensive tool for electrical issues with these old trucks . A VOM meter is good too but for the issue your looking for a test light will be the only thing you'll need .
Hook the one end to the neg terminal of the battery and the other to the pos to check your test light(have been know to have a bad bulb in mine a time or 2 ) battery then move it from the pos post to the body . If no light = good ground , if it lights your got to fix the grounds from your battery to your frame and body .
You then just follow the wiring diagram using your test light till you find where your light stops working , or go the other way from where you know it's bad back toward and battery feed .
Let us know how you make out

[67 chevelle]

Originally Posted by midniteblues

check the main power wire going into the bulkhead ive had that connector corrode in the bulkhead and cause problems.

I had power everywhere under the hood and nothing in or going out of the cab.

had power up too the bulkhead but nothing on the otherside at the fuseblock.

wiggled jiggled that dang wire and notheing.
finally disconnected the bulkhead from the firewall dug out some of the tar like sealer and pulled the connector outa the plastic guess what the spade connector came out in two peices.

even though i wiggled and jiggled it wouldnt come out and it felt solid but i knew there was a problem with with it.

I had this happen on two trucks

yeah that bulkhead is a joke , and newer trucks have a bigger charging wire out the back off the alternator than our old trucks had going from the battery to the starter ,,, upgrading the wiring is a must on these trucks , not very good from the factory ,, add ad 45 years and its horable
that bulkhead has a 3/8s nut on it