1994 Chevy K1500 4wd pick up with the 4.3l, is it the ignition switch?

check your wiring harnesses and fuse box. Something has been disconnected, find out which connector is disconnected. Trace it back from the malfunction- Burnt bulbs can be the cause of over-voltage from a malfunctioning voltage regulator, or of normal wear and tear~ list your difficulties one at a time or you may confuse the guru.

The speedometer is not functioning, the truck drives but doesnt shift out of first gear and yes its a automatic, andreplaced the speed sensor and the heat isnt functioning other than that the truck is fine. I already check the fuses and the wires unless i miss 1 plug under the truck that i cant see but other than that it works fine.

...at this point, we're going to have to get scientific. A test light what glows under the presence of 12V would be handy--a reliable electrical schematic and box of colored pencils will be needed to track each circuit, that we will test to make sure that each one is complete-

the firewall frequently has connections that jiggle loose. My toyota would go "blind" for moments at a time. The roads around here are crater filled (clearlake, CA) and tortured the wiring connectors. A quick "push it back" into place fixed the problem. You could try re-pushing all the connectors back into position before getting scientific-

ok

Many problems are created by a corroded positive terminal. Clean off all corrosion with a brass wire brush and use some electrical cleaner. probably are four lugs that need your attention. Dont forget the positive terminal.

,,,er the ground lug-----both ends! Your electrical system will be sparkly-fresh and good as new.

ya i bet lol