1970 F100 starter staying on

[BlackKnight0814]

So I'm not an electrical guy at all. I have a 1970 F100 that someone dropped a 400 modified into and has messed the wiring up, me thinks. Most everything works fine. I've replaced the solenoid, ignition switch, and starter, as well as battery. And it seems that something is different every time. Sometimes I hook the battery up and it instantly sets the starter off. Or sometimes it won't do anything at all. And sometimes it will let me put the key in and turn it to start position and then will stay on. I've had everything tested at Napa and it's all good. Is there something I'm missing? And has anyone else ever had this problem? Lately it's been doing nothing and I have to turn the hazards on then off to get it to even do anything. I'm being told it's a short somewhere but I'm a little weary about cutting into my harness. This only started about 2 weeks ago. It didn't have this issue before.

[sargentrs]

Check the wires at the terminals on the solenoid. You might have them backwards. Been there, done that. If the original wires are still the same, the brown wire goes to the "I" terminal (the one closest to the cab).

[BlackKnight0814]

Thanks, but I've tried that. And even have disconnected every wire but battery and starter and it still has done it

[sargentrs]

Have you replaced the solenoid? They are notorious for being bad right out of the box. How about your ignition switch? Here's the wiring diagram for your truck http://www.fordification.com/tech/wirin ... master.jpg Don't be intimidated by it, I was new to wiring when I got started on my truck 5 years ago. Since then, I had a Dodge that forced me to learn to read these diagrams. Up in the top left you'll see the starter solenoid that's mounted on your inner fender. Wire number 32 (originally red with a blue stripe) goes to the "S" terminal on the solenoid. This is the wire that triggers the starter when you turn your ignition key to start. This is a pretty clean, straightforward circuit. Trace the wire back to the square 4 pin connector shown in the top center of the diagram. I'm not exactly sure where it is but you should be able to follow the wire back to it. I think it's along the firewall. Look for any frayed or melted wiring or connectors. Then follow that plug back to the flat 4 pin connector shown at the bottom center of the diagram, again looking for signs of bad wires (either right before entering the firewall or under the dash). Lastly, follow wire number 32 from that connector back to the ignition switch. If the length of the circuit all looks good, then grab a voltmeter and start testing connections where wire number 32 is. To start with, you should have zero volts at the wire going to the starter or to the 2 small terminals on the front of the solenoid. When the key is turned to start, you should then see 12v going to the starter cable. If you're getting power to the starter cable as soon as you turn the key to "on", then suspect the solenoid or the ignition switch.

[BlackKnight0814]

I've changed the solenoid twice and had it tested that's all still good. As well as the ignition switch. But it's starting even with my ignition wires off the solenoid.

[sargentrs]

If it's starting without the wires attached on the front of the solenoid then most likely your new solenoid's bad. Really not that unusual. Try this...remove all wires from the solenoid except the battery + cable on the front and the starter cable on the rear. If nothing happens, then start adding wires back on one at a time until one of them triggers the starter. That'll be the starting point (no pun intended). . The only other wires come from the voltage regulator and alternator.

[BlackKnight0814]

You're awesome randy. I finally caved and spent another $20 and as it turns out not all 4 post solenoids work. The wiring on the inside apparently is different. Went with the original style and it fires right up.

[sargentrs]

Excellent! Glad she's working again.