I just finished putting in a low mileage cummins in my truck and when I turn the key to start, it will not turn over. I have power to the FSS but don't hear the grid heater cycling. Haven't checked with a voltmeter yet to see for sure if it is getting power. Funny thing is one of the last times I tried to start when I had the previous engine in, it did this exact thing. I put the engine and wiring harness from the donor truck in this truck and everything was working hunky dory in the donor. I am leaning towards the ignition switch but don't know how likely that is? It has the getrag and the neutral safety switch is out and is jumped. It has been like that for a while now, so that eliminates that. Also tried different relays for the starter. All grounds in the engine bay are good that i can see.

 

Have you tried jumping the starter with a screwdriver? If it cranks over and starts then it's a wiring issue.

Is the wiring systems all 93 vintage?

 

I haven't yet, but assume that it would not be a problem to start that way since it worked fine in donor truck very recently. I have the engine wiring harness from donor truck as well where everything worked fine together before. Fusible links all seem fine.

Just before I took out old engine and old wiring harness, it did the same thing.

 

Don't assume anything.
Test the starter by jumping to the solenoid terminal
Then test the relay by energizing the coil terminal
Then grab a diagram and follow the circuit from there with a meter or test light.

 

Jumped the starter and it turned over fine.

Tested the relay by touching a wire to the brown wire coming from the relay to the positive terminal on the battery. Turned over fine.

The relay is not energizing when the key is turned to starting position. Can not here it click.

 

OK, so all that's left is the yellow wire to the ignition switch (including the neutral safety switch connector that's jumpered), and the switch itself. If, when the switch is in the on position the windshield wipers work, you can assume the switch is getting power on the circuit that should power the starter relay.

 

Thanks for the tips, I will check the other things you suggested in the morning and see what happens.

 

I tried out a new ignition switch and it is still doing the same thing. So I jumpered the yellow wire from the ignition switch to the yellow wire on the clutch safety switch and still got same result. where does the other yellow with black tracer wire that is on the CSS plug go?

 

Should go to the starter relay coil.

I assumed that when you said that you jumped power to the starter relay that the ground side circuitry was OK, as it wouldn't close if it weren't

If you were to go after this with a diagram in one hand, and a test light or meter in the other hand, it should be about a 10 minute exercise. There just isn't that much to it. Trying new parts is about the most expensive and frustrating way to tackle the problem.

If you don't understand how to do that, hire someone that does. It'll be cheaper in the long run.

 

I definitely am not the best at electronics but I am trying and in doing so hopefully learning a little more in the process. I took the ignition switch back so I am not out that money.

I have poked around for a diagram on the net but only found what seemed like a partial one.

I'll just keep trying when I get back into town in a few days. Only other thing I can think of right now is checking the red wire supply from the battery to the relay.

 

The relay wiring is very simple. Large red wire is bat +. Brown wire goes to the starter small terminal. Yellow wire should be hot when key is in the start position. The last wire goes to either the clutch switch (manual) or the neutral safety switch (auto) either of these just complete the ground circuit. So if you jump that wire to ground and it works then you have a problem in the ground circuit. Either your previous jumper on the clutch switch is bad or the ground on the other end is bad.

 

I am getting 12 volts to the yellow wire at the CSS and relay when i put the key in the start position. I can also tell the grid heater is not coming on but the wait to start light is.

 

The last wire goes to either the clutch switch (manual) or the neutral safety switch (auto) either of these just complete the ground circuit. So if you jump that wire to ground and it works then you have a problem in the ground circuit.

I doubt it's cold enough down there for the heaters to come on.

 

I was going to say, don't you mean up there?, but I see that you are almost even with Houston, so it would be over there......Mark

 

Got it figured out finally. It ended up being the connection at then end of one of the wires in the plug that goes into the relay. Wasn't making a good connection to the relay.

Ended up trying another relay that I have from the previous wiring harness for a second time and gave it a good wiggle when plugging it in. Busted right off.

I forgot about the heater not turning on in warm weather. Just so used to it coming on every time all winter. Just getting pretty hot here. Truck is in Tyler TX right now while I am getting it back together.


Thanks for all the help!