Starting truck

Might want to check your ignition switch, and the wires leading to the starter selenoid.

 

Might search Delco Remi voltage drop tests.

 

can you tell if it is the relay clicking or the solenoid on the starter?

 

If it is then your getting power and ground to your solenoid that transfers power from your batteries to your starter motor. So if thats the case and this only happens sometimes it could be a few things, you have an intermittent bad connection (power or ground) at the batteries, starter or starter ground. You could have a starter motor starting to go bad. Could be a solenoid not transferring the power to the starter motor. Could also be a power or ground cable starting to go bad. Keep in mind its not just the cables to and from the starter. Its every cable. You can trouble shoot fairly easily with a meter and a test light and somebody to turn the key.

 

Then your relay is being triggered by your ignition switch to send power to engage your starter solenoid. Power goes from your starter fuse through that relay (when it clicks and engages to let it through like your hearing) and then down to the starter solenoid. Once that power reaches your starter solenoid it should engage your starter as long as the solenoid has a good ground. If your starter fuse is good you just need to get a test light and have some turn the key for you while you test for power down to your solenoid and make sure it has a good ground. If its all good check for power on the big post of your solenoid passing through to the starter motor when the key is turned.

 

39mt have another relay on the starter.
I always just take that off. Just another thing to go wrong.
Truck oems already have a starter relay on the fire wall.
So just connect that wire coming from truck relay directly to starter seliniod.
Bypass the relay on the starter all together.

Ive done that to the last 3 trucks ive had. No problems.