truck dies when i turn key to on position

hey guys as the tittle says i can start my my truck but i gotta leave the starter engaged in order to keep the motor running. i have already checked the battery and battery tested good. i put in a new electrical side of the ignition switch in from a 86 or 87 b200 and that wasnt it. what else could it be. ima bout to hit the junkyard up for a new ignition tumbler where you put the key in lol. but after that im guessing the ecu aka the main computer is at fault. but i dont have 500 freakin bucks for a new one and none of the junkyards in my town have a 2600. i really need help here guys i wana start my truck so bad. thanks for your help guys. and any help is appriciated.

Did you put an actual brand new never used electrical part of the ignition switch, or just one from a junk yard...? If the latter it could still bee the switch... When you sure it up see if you can wiggle the switch on the way back from the start position to see if you can get it to stay running... It still sounds like its electrical switch related...

out of a junkyard. cuz i dont wana pay the 100 bucks for a new one. but my stock electrical side ignition switch was the same way. im still at a loss.

Did you actually TEST the original switch or the one from the parts yard to see if it was bad before replacing it? Guess, what, most likely NOT the tumbler portion of the switch unless the rare chance that the cog broke off.

You need to learn to test stuff to KNOW what's wrong, not just throw parts at it. I have two used electrical ignition switches from the parts yard. But I won't sell to you, you're just doing shotgun. Get a voltmeter/multimeter for $10-$12 at Sears on sale, or $3 at Harbor Freight, and learn to use it.

If you needa computer I have one for a b2600I 4x4 stick

first, check that your lights come on on the dash and stay on at the position before 'start'. these mazda's are bad for that after all these years. my 88 i have to find just the right spot... it's very touchy

Lance he's got a carb'd g54b so your computer won't work. I'd say you just got a bad switch from the jy... I picked up several last time I went to pull a part just in case one or two that I got from the yard happened to be bad...

only thing is dono how to test all the switches and plugs that go from and to the switch. and i have a volt meter. and the only thing is all the jy had the one that i went to was one that was in the range of my truck. cant use anything above 88. but it looks like ima have to break down and buy a new electrical side of the ignition switch. damn it all well. but the only thing is, it would start and stay running on the old starter before the nose cone broke off and had to pull it. since installing new one i have had all these problems. im just at a loss lol. and i also dono whats spose to have power on what wire and when. thats my only down fall. and thanks for the help guys still tryin to learn this truck lol

they should all be the same, 86-93... i cant imagine they would change the wiring of the switch when they kept the style the same for that many years... i only noticed a difference between the looming protecting the wires when i got spares...

when i took it out of the donor truck it looked exactly the same as my old one lol. and everything fit just like the old one lol. just hopin i could figure out wtf the problem is. what it could also be is the solenoid on the starter. but its a reman and it should be good. never had a problem with a starter till now.