2001 Jimmy: Any electrical system geniuses out there?

It was having strange electrical system problems before... Relays suddenly going bad (first the fog lamps; then the DRLs); the gas gauge suddenly dropping to zero with 3/4 of a tank of gas in it -- and just as suddenly coming back up to tank contents; the lights on the 4WD panel flashing in unison, then reverting to current operating mode. So when I went to have the intake mani gasket replaced (yet another problem that surfaced on this bird, all pretty much since I bought it in July 2009), I figured, as did a few other mechanical minds, just replace the fuel pump; that should fix the sending unit problem. And while we're under the hood, replace the plugs and wires; probably hadn't been done since the truck was built.

But after replacing the fuel pump, the only way the mechanic could keep it running was to wire it directly to the battery and control it with an external switch. He also told me that the fuse block under the hood was terribly corroded, as though exposed to a lot of salt water. Well, it had no cover when I bought the vehicle. So I got a replacement block from a junkyard. No change. I bought a new ECM. After that, not only did I have a problem with the fuel pump (the engine would get hot; then the fuel pump would stop running), but now I also had a problem with the dash: No tach, no speedometer, no odometer. And when the truck left me stranded on the highway after picking it up from the first mechanic, I took it to another. And now, I understand from the second mechanic that I have no gauges at all.

A friend of mine told me his grandfather's Blazer had a similar problem, which was corrected when they found some loose wires on the underside of the alternator. We checked: Nothing loose there.

I have no idea what's going on here, nor does the original wrencher, nor does the second mech. Do any of you? I really don't want to have to buy another vehicle so soon.

Thanks, everyone.

It was having strange electrical system problems before... Relays suddenly going bad (first the fog lamps; then the DRLs); the gas gauge suddenly dropping to zero with 3/4 of a tank of gas in it -- and just as suddenly coming back up to tank contents; the lights on the 4WD panel flashing in unison, then reverting to current operating mode. So when I went to have the intake mani gasket replaced (yet another problem that surfaced on this bird, all pretty much since I bought it in July 2009), I figured, as did a few other mechanical minds, just replace the fuel pump; that should fix the sending unit problem. And while we're under the hood, replace the plugs and wires; probably hadn't been done since the truck was built.

But after replacing the fuel pump, the only way the mechanic could keep it running was to wire it directly to the battery and control it with an external switch. He also told me that the fuse block under the hood was terribly corroded, as though exposed to a lot of salt water. Well, it had no cover when I bought the vehicle. So I got a replacement block from a junkyard. No change. I bought a new ECM. After that, not only did I have a problem with the fuel pump (the engine would get hot; then the fuel pump would stop running), but now I also had a problem with the dash: No tach, no speedometer, no odometer. And when the truck left me stranded on the highway after picking it up from the first mechanic, I took it to another. And now, I understand from the second mechanic that I have no gauges at all.

A friend of mine told me his grandfather's Blazer had a similar problem, which was corrected when they found some loose wires on the underside of the alternator. We checked: Nothing loose there.

I have no idea what's going on here, nor does the original wrencher, nor does the second mech. Do any of you? I really don't want to have to buy another vehicle so soon.

Thanks, everyone.

THE FIRST TWO MECHANICS AND WHO EVER REPLACED THE FUSE BOX.:rofl:

Without seeing it and checking it out we can not say.
But from what you have told us you have a wiring or electrical problem or even bad ground.

If you are not good on electrical work find a good repair shop/mechanic/tech that is.
Check around Ask around
Word of mouth.
Family friends coworkers neighbors business people and delivery people.
Mailmen and parcel delivery people get around and notice a lot of stuff.
Even a good parts house knows what shops are good and not good.
Chamber of commerce and better business bureau and city hall.
If you find a good referral to a repair shop go look them over and talk to them.
Look for a clean looking busy place with nice people running it.
Ask a few questions and ask about their qualifications and training.
Not all places have trained tech/mechanics.
If they do not find a place that does.
Even all dealers do not have all trained techs/mechanics.