No wiper power, no radio, no blower (heat/cool)

[GMC3500HD]

Hi all,
I have a 1996 GMC 3500 HD w/ 85000 miles on it.
Suddenly and simultaneously my windshield wiper won't turn on, my radio stopped working and no air is blowing from my vents. Checked all the fuses both on the left side of the dashboard and under the hood and all are fine. Checked for 12V at all the terminals and have it. At this point I'm assuming a relay has crapped out because of all 3 failing at the same time. No voltage to the windshield wiper blower or fuse terminal for these three components. Does anyone know which/where the relay is found? What else could it be? Thanks much in advance....

[racer55]

Sounds more like a ground problem to me.
Try running a secondary ground to the wiper motor mount attatched with vise grips and touch the other end of the wire to battery ground and observe the results.(wipers should be turned on)
If the wipers run,then you found out you have a bad ground.Check all of the ground points on the back passenger side of the engine intake bolts as well as the body to engine and frame to engine grounds found back there.
Also don't forget about both ends of the battery ground cables.
Perhaps I am missunderstanding your post,when you say you have voltage at all the fuse terminals,then no voltage at the fuse terminals I get confused.

[GMC3500HD]

Sounds more like a ground problem to me.
Try running a secondary ground to the wiper motor mount attatched with vise grips and touch the other end of the wire to battery ground and observe the results.(wipers should be turned on)
If the wipers run,then you found out you have a bad ground.Check all of the ground points on the back passenger side of the engine intake bolts as well as the body to engine and frame to engine grounds found back there.
Also don't forget about both ends of the battery ground cables.
Perhaps I am missunderstanding your post,when you say you have voltage at all the fuse terminals,then no voltage at the fuse terminals I get confused.

Racer, thanks for you reply.
I have voltage at the fuse terminals leading to all the accessories and lighting that work, and only those that have ceased to operate, i.e., the radio, blower fan, and the wipers, have no voltage at their corresponding fuses. When I pulled the relay associated with the the working components, the fuses had no power. When replaced, power was restored. Ergo, given no power at the fuses for the non-working components, my amateur brain surmised that it must be a bad relay. The fuses are fine, and offer no abnormal resistance (though I replaced with new anyway). However, none of the relays except those under the hood are labeled, and I have no wiring diagram. There are a two relays under the steering column which checked out fine. Perhaps I was overly optimistic? A ground issue seems like a hornets nest of fun, but I appreciate your pointing me in the right direction.

One interesting thing happens. When I press the dial on the radio--which would normally turn it on--the digital time appears before fading out after a few seconds. Does anyone know why would this happen? Also what exactly is the purpose of the "radio battery", which does have an energized fuse associated with it?

[racer55]

As far as I know the radio battery is to power the keep alive memory in the radio.
With your new description or clearer description if you will,I would say that there is a problem with the accessory circuit in the ignition switch.
Do you get any power at the items if you turn the key backwards to the accessory position rather than to the run position?

[GMC3500HD]

Incidentally, about a week ago, the ignition key got stuck in the "on" position, and would not turn back to off. Removing the 50A ignition fuse under the hood turned off the engine. Until recently repaired, to turn on the engine I would have to replace the fuse and turn the key forward to "start" (it turned forward fine to "start", not backwards). A locksmith fixed the key issue. Unfortunately I don't know the nature of the repair.

A word on this matter. My brother was using the truck at the time. That morning he turned the key on to energize the glow plugs, then turned it to start when the "wait to start" light went out.

He says that when he did, it felt like the ignition cylinder spun "too far", as if it slipped past "start". It fell back to "on" and he went about driving to his call. Upon arriving at the customer's house, he was unable to turn the ignition key off, and pulled the fuse under the hood. He replaced it after finishing the call and until it was repaired a week ago, that how he got around. When a locksmith finally addressed it a week later, I assumed it was a tumbler issue that he repaired. I have yet to get his bill to see the invoice, and he's in Brazil until November .

What is meant by addressing the "linkage" with respect to the ignition key? Might this be related to the power issue with the mentioned accessories? And finally, could pulling the fuse each time the truck needed to be started and stopped have affected the circuitry for the radio/wiper/H&AC?

Thanks in advance. Great site...

[JohnC]

Sounds like there's a good chance the real problem is the ignition switch, not the lock. AFAIK, all the functions you have issues with are powered by the accessory terminals in the switch. There is no relay. If the switch has failed mechanically that could explain the "key" issues as well.