91 crew cab electrical snafu

[scotto0609]

A little back story. during the summer i chased a rear lights and tranny problem,they are now fixed.In doing so i replaced 2 out of three vss switches and stripped the whole rear wire conduit. Being paranoid I put conduit and tape and then zipped tyed everything back. Now i keep blowing the idle/gauge 20a breaker. All lights continue to work. I lose the speedo,amp,fuel gauge and the alternator drops off line along with the headlight on chime comes on whenever i turn lights on and stays on. Sometimes i can change fuse and it will idle all day and sometimes it blows instantly turning the key on . I really am wondering if it can be a bad alt or headlight switch or the one vss i didnt get to.. My thoughts are I am ripping all that conduit off and starting from scratch. Am i overlooking something, any help is appreciated. thanks

 

[dyeager535]

Your alt is probably not charging because you are losing the cluster...the battery light in the cluster is what acts as the resistance necessary to get the alternator to charge.

I don't see where you'd have much choice except to strip everything and find the short. I'd use the 91 electrical manual (link below) to make sure you were looking at the right circuits though. At least that fuse blowing will tell you where it may be.

http://67-72chevytrucks.com/vboard/showpost.php?p=5621043&postcount=1

 

[scotto0609]

Thanks I was looking for a wiring diagram,all i have is a 87 one. Yea I was hoping it was something simple without having to rip up the harness. I really dont use the truck that much and its getting cold here. And of course its raining today!

 

[nvrenuf]

Not sure if it will help but look at this thread I had about my '91.

https://ck5.com/forums/threads/alternator-not-charging-fixed.323721/

Definitely have the alternator checked!

 

[scotto0609]

Crawled under today and tugged pulled and pushed every wire in the truck to no avail. Drove it twice and the fuse blew both time by 1) hitting school rumble strips and 2) hitting a big bump in road. Tried duplicating while pulling pushing and shaking wires,no joy. Even took a ball peen hammer to alt and tried tapping it with no pop of fuse. Going to take it out in a few for a tree and a cigar and see what happens. On a bright note found a leaking vacuum line and my heater control and cruise work betterer!

 

[dyeager535]

Just positing here, I suppose you could disconnect the alternator and drive it, no? If no issue you know it's the alt. If issue, you know thats not the problem.

 

[scotto0609]

Kinda had that thought today disconnected when it was running and nothing. going to try that after my chores or tomorrow,thanks great idea!

 

[diesel4me]

Did you look real close at the harness where it goes from the alternator to the rear of the engine near the bellhousing ?...there is a factory splice there where two or three thick red wires join,I've have them rub through or chafe against the dipstick tube and short out when you go over bumps..those wires go over to the starter solenoid and feeds power to the junction block near the PB booster and then to the fuse box..

Sometimes where the two halves of the fuse box bolt together gets corroded,that can cause fuses to pop for no apparent reason too..