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Starting problem

3K views 36 replies 6 participants last post by  markwemple 
#1 ·
99 f250 sd cc.

Turn the key, nothing happens. All the idiot lights are coming on. Double checked charge at both batteries. Pulled starter and bench tested, its fine. What's next??
 
#7 ·
When mine did that it was the fuse under the hood. I think it's a big 15 amp fuse. Acted just like yours, everything came on but no engine turn over. Replaced the fuse and that was it.
 
#8 ·
I'm having to do this single handed, so I can't turn key and check for power at the same time. I'll check the fuse. (didn't realize there was one, only the relay) Anyway, re-installed starter, cleaned all contacts and grounds down there and nothing. Ran through the gears while trying the key, nothing. Switch is working for reverse as the lights come on (PO installed a back-up alarm) So next is fuse and relay.
 
#12 ·
And when you manually put (+) & (-) to the two sm terminals of that relay (pass side, under hood - right?) does it crank it over?

If so, the problem in on the "key" side (Key sw, NSsw, or associated wiring/supply).

If not, the problem is on the Power side (cables, terminals, connections, batteries) or the Starter / Bendix.
 
#16 ·
No, you don't need assistance with this, you can do it on your own....

The starter relay is at a midpoint in the system. You need two jumper wires (light gauge like 16 because you're Not running much power thru them, just want to energize the coil in the relay) that you can manually put power into the coil from the battery. Doesn't matter what goes where, just disconnect the two existing SMALL wires from the relay and put power/ground into them (creating a magnetic field that will close the contacts inside to throw Big Battery power to the starter).

Because it is in the middle, it will help you narrow-down which half of the system is giving you trouble.
 
#18 ·
Here's how that relay works. The two sm terminals need power flowing thru them to create the magnetic field that moves an arm inside that connects the two larger terminals.

The key is what completes the circuit to get that power to flow thru the coil.

Once the arm moves and connects the two large terminals together, power flows to the starter.

This is the basis for most relays, they use a small amount of power to switch a Large amount of power On/Off (you can imagine the complications of trying to run battery cables up the column to the key ;) )

So, sometimes relays have an internal power supply to the coil (comes from the terminal with the cable connected to the battery) and the One terminal that's left supplies Ground, from the key, to energize the coil and turn the starter on. BUT, if you have Two little terminals I think they should Both be connected to something. If you have a missing connection there it would act just like your symptoms now.

With this understanding of how it works, you should be able to diagnose what you have. Take a testlight or meter and see if that unused terminal had power in it or what happens if you ground it with a clip lead. Try disconnecting all the terminals and put power & ground into the sm terminals, you will hear the arm move inside with a big "clunk" to know its working. Then add the battery side Lg terminal and see if power appears at either sm one. - That kind of stuff....

You might have found your problem though :)
 
#26 ·
OK, so what you've done is to by-pass the relay and make the connection manually. The relay is new - right? And you had the problem before you changed it so I'm gonna assume it's Good.

That means the problem is on the Key Side. Do you have a testlight? What is the sm wire that's on it doing when you roll the key to start? Is power being applied? Ground? you should see something in that sm wire when you go to start.

If not, trace it back. I think the NSsw is between the key and the relay. Do you find something happening there? (at the NSsw?) Is the keys contacts getting that far? (I want to pick the next thing in the "middle" to know which side the problem is on now...)
 
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