1987 F-350 6.9 litre diesel Cab and Chassis dually 4x4 with 5 speed manual transmission that I can not get to crank or turn over. Batteries are good, power to the starter relay from the ignition (small red wire to starter relay on fender well-small post). If I cross the large posts on the starter relay with a screw driver while in neutral it will not turn over like I have done in the past. Is the starter selinoid on the starter itself stuck? Bad starter? I hear one click when I turn the key to start and that is it. It was starting fine just a couple of weeks ago. It set for a couple weeks and it wouldn't crank. I figured it was a loose wire from the ignition to the starter relay (that has happened before) but that checked out with a test light when key turned to the start position. So I tried jumping the two big posts on the relay as I have done in the past and got nothing. I figured the relay must be bad, so I replaced that but still no dice. Still nothing. The relay had power to the hot post both before and after I replaced it. Any ideas/thoughts would be much appreciated. Thanks!
Ben in Maine

 

New batteries can go flat, in fact they may have never been fully charged to begin with.

A couple weeks sitting (with maybe a parasitic draw on the truck) - well, there you go. Not doubting you, but how do you know for certain the batts are good? If you disconnect everything and measure the open circuit resting voltage of each battery each should read 12.8 (fully charged) 12.0 is dead.. etc.

 

I put the batteries on a charger/tester and they were fine. I have let it set for well over a couple of weeks in the past and the batteries have held. I am getting absolutely no cranking when I turn the key, but the even the battery gauge on the dash comes up to about 13 when I turn the truck on. They are pretty new batteries to boot. I am very confident that it is not a battery problem,
Thanks for the reply!
Ben in Maine

 

One, you really should get yourself a digital multimeter for testing voltage, resistance etc. $5 at Harbor Freight.

Two, I'd grab a screwdriver and go under the truck. Short the small terminal on the starter to the big one that's connected to the battery cable. (There are three terminals, one to the battery, one going inside the starter, and a small one to engage the starter). If the starter, batteries and cable is good, you should have it crank.
If not, it could easily be the starter. Starters these days seem to fail often and store-brand starters are luck of the draw.

 

When you hit the key, or jump the relay with the screwdriver, do you hear a loud CLICK down below, by the solenoid? If so, check the wire between passenger side battery and the starter, the main motor wire. ESP. check the terminal right at the starter. This is EXACTLY what happened to us a month or so ago, and that terminal had just snapped off at the point where it takes a 90-degree bend.

We were on the road, so we put a jumper cable between the right positive post and the terminal on the starter (DISCONNECTED BOTH NEGATIVES, of course). That allowed me to start it from the key. Autozone didn't have a big enough terminal for that big 2/0 wire, so I fabbed a side-post battery terminal to go over the remains of the terminal on the end of the wire. Found a 2/0-capacity 3/8"-ring 90-bend terminal online after we got home.

That 90-bend on the terminal is a weak point.

 

First make sure engine will turn over by hand put a socket and breakover on the bolt on the end of the crankshaft turn engine a complete revolutions. If it does turn over then its back to electrical. Check your grounds, Put power on the the small wire on the solenoid on the starter. It should turn over. If not as the man said get VOM meter and start checking circuits.

 

I'd say if you are getting power to the switch terminals of the relay and solenoid that your ignition circuit, through the clutch safety switch, is fine and you should look at your connections and cables. I have seen terminals and clamps that appear fine, permit small light and radio power loads, but lose it all when a major load is applied. Sometimes these connections will get hot or visibly smoke. You could use a test light and touch the connectors and/or cables while this load is applied. If the light goes out when the load is applied the problem is upstream in the power circuit.

You can have someone put the truck in neutral and push in the clutch and hold the ignition while you take a phillip's blade screw driver (or the tip of a test light) and press in between the connection of the battery terminal and clamp, making a back and forth twisting motion. If the connection is bad, it should jump through the screw driver and power up to the starter or complete the circuit to ground.






Always wear your safety glasses and protective gear.

Always wear safety equipment. These tests will usually work for any connection. Be especially careful when working near the battery or when working around combustibles.