Intermittent voltage drop, fixed by jump

[TX87R10]

Sorry to ask yet another question but I ran wires in to the cab to a button to temporarily make sure the truck is drivable so I can diagnose ANOTHER issue with the truck not starting. It's possible it is the same issue but with the button the truck will usually start, with cranking the key it will not.

I check voltage into the starter when not engaging the button and it is 12v. After depressing sometimes the voltage drops to 8v on both lines and the truck will not start. Oddly if I get under it with a screwdriver and jump the starter solenoid the button will work again to start for a short period of time, before not working again.

I pulled the ground strap off on the passenger side firewall and cleaned and tested continuity it was good. I checked the two beside the radiator on the passenger side and they were good as well. Same thing with the one that the A/C blower attaches to.

I am at a loss because when I check things one at a time I am not finding what is going wrong, but magically jumping the starter runs the gremlins off temporarily.

Anyone have an advice? I have the wiring diagram for the vehicle but everything I am checking looks ok.

 

[TX87R10]

BTW from a previous thread I'll add that I did have the starter checked twice too and it is good, battery is good.

 

[Raider L]

@TX87R10,
It sounds like a similar problem that I had and it was the neutral safety switch had gone bad. I did all you did and the truck still would not start but sometimes it would. I never knew when I got out there if it would crank. I replaced the ignition swiotch and it wouldn't start. What I did that should have told me that it was the nuetral switch, was when I tried to start the engine with a remote start switch. When I pulled the rigger, same kinda like you did with jumping the starter, in youir case it did crank the engine, but in my case it didn't. I was at a total loss as to what it could be. Until I thought of the only thing I hadn't checked and that was the neutral safety switch. I replaced that and the truck has been starting ever since.
It's the switch most people, including me, never think about being part of the start circuit. So, replace the neutral safety switch and you'll be able to put in button start or whatever you want so long as you make sure it's tied into the neutral safety switch and it will work.

 

[Ricko1966]

Your push button switch performs the exact same function as jumping the solenoid with a screw driver. It completes the circuit from the 12 battery hot, to the solenoid engage terminal. That being said,if it cranks everytime you jump it with a screw driver,and intermittent with your pushbutton,you have installed your push button wrong, you have a bad pushbutton,you have a bad connection or compromised wire from the starter to the push button. If you installed your push button as I directed you. The neutral safety switch is not part of the equation. Did you ever check all battery connections,and be sure you have a good ground,battery to engine,battery to body,battery to frame.

 

[TX87R10]

Your push button switch performs the exact same function as jumping the solenoid with a screw driver. It completes the circuit from the 12 battery hot, to the solenoid engage terminal. That being said,if it cranks everytime you jump it with a screw driver,and intermittent with your pushbutton,you have installed your push button wrong, you have a bad pushbutton,you have a bad connection or compromised wire from the starter to the push button. If you installed your push button as I directed you. The neutral safety switch is not part of the equation. Did you ever check all battery connections,and be sure you have a good ground,battery to engine,battery to body,battery to frame.

I think you are right. It was a poor connection to on the solenoid. I redid the wire with an eyelet and made sure the ignition wire in is not part of the equation anymore.

I did check connections, grounds, batteries, etc... I think the underlying issue is in the ignition switch but the temporary push button had its own issue that is hopefully resolved now

 

[TX87R10]

Next weekend is going to be diagnosing the ignition not working properly.

 

[Ricko1966]

I told you we would get to actually diagnosing the reason you can't start it with the key when you have time. When you have time remove the ignition switch electrical portion from the column. Reconnect your starter as factory. Slide the ignition switch to the end of its travel with a screwdriver. If the starter cranks most likely the ignition switch rack in the column has cracked

 

[Ricko1966]

Back when you started on this mission I asked you to be sure you had a 3 point ground. Battery to body,battery to frame,battery to engine. It doesn't necessarily need to be 3 wires,homerun to battery,could be battery to engine,engine to frame,frame to body. But all 3 need to have a good ground. Nothing on your car draws more amperage than your starter. I would ground the battery directly to the engine,then ground your frame and body to the engine.

 

[rusted nuts]

I think you are right. It was a poor connection to on the solenoid. I redid the wire with an eyelet and made sure the ignition wire in is not part of the equation anymore.

I did check connections, grounds, batteries, etc... I think the underlying issue is in the ignition switch but the temporary push button had its own issue that is hopefully resolved now

If You run out of stuff to check try a new solenoid.