Electrical problem-short

My son is offering me his 2000 Chevy 2500 van. Price is good- free. However, this truck has endured a rough life. Didn't carry heavy loads or anything like that, but no real maintenance. Needs the entire brake system repaired. Has never had a tune-up, but runs decent. Abysmal gas mileage, in part because he has never emptied out all the crap inside. A good 800-1000# in there. No rust,no body damage, good V8. Biggest problem for me is a short that blows the fuse that powers all the instruments and speedometer. Put in an oversize fuse- pop. I can assume that the problem is under the dash, but do not know squat about this kind of troubleshooting. Has been driven like this for quite a while, allowing his ex-installer to get a couple of speeding tickets. Because none of the warning lights work, drove the truck with almost no brake fluid. How do you suggest I attack this, or just take it to a pro?

new dash harness and be done with it, if you can buy just the dash section
that'd be the easiest route I would think

I recall this being a common problem. Damned if I can remember what the cause is. I'd like to say that the problem starts with corroded wires in or near the underhood fusebox.

PCM corrosion is another huge problem. The case is aluminum and underhood, the aluminum corrodes and squeezes the circuit board, causing all sorts of bad things.

Somewhere there is a short to ground. Look for bare wires or wires rubbing together.

It's the "somewhere" part that worries me.

I'll check the diagrams tomorrow when I get to work. And pick some brains. The problem, again, was not uncommon. GM put the underhood fusebox in a rather bad spot.

Another thing to look for - does the truck have any aftermarket equipment in it, or once in it then removed?

Remembering now that one of the instances was caused by a bad (OEM) radio.

Have had no aftermarket radio etc added. Has a factory radio. Very much appreciate the help.guys. My electrical troubleshooting has been limited to alarm systems, this scares me, but will tackle it if it does not require I put my old, large, body under that dash. Don't have a Japanese gymnast available, either.

Short diagnostics 101: It's all about isolation. You know one fuse that blows. Dig up wiring diagram and find which items are powered up by that fuse, unplug them all, then put a new fuse in. Reconnect items until the fuse blows.

If the fuse blows with everything unplugged, then you need to start unplugging chassis connectors (labeled Cxxx in the diagram, and the 3 digit number actually corresponds to where the connector is in the car - underhood, in cabin, left side, right side, etc) and reiterate.

Hopefully you don't need to go that far, but hard (not intermittent) short problems are almost always bad modules, followed by corrosion in a harness connector, followed by a chafed wire. So it's not nightmarish to find, just time consuming.

Thank you, knurled, that sounds doable. Don't have access to the truck yet, has to go in for the brakes. (I will not do that , and he is paying for it )

What knurled said.

I had a key off battery run down through the instrument cluster circuit (but no direct short) w/ an '02 PU. Isolated it to the IC by disconnecting radio and heater controls on that circuit, continuity tester w/ buzzer made it easy.

The PU ICs of that era were notorious, not sure of the vans though. Also found mice built a nest in the bottom of the electrical center box and chewed insulation off a dozen plus wires that could make contact. Grounds too, there were about a dozen, might wanna clean body to chassis grounds... they were terribly corroded. Removed all aftermarket stuff too.

Nobody here remembers the major problems on trucks that old, oh well.