I have a ’97 U320. Looking at the diagram, if you checked the wires from the battery to the starter (+ & -) and they look good, I would look to the “AUX START SOL” to be a possibility. On mine, it is on the driver’s side behind the rear wheel with the boost solenoid. The boost sol is the one on the right. Try jumping the “AUX START SOL”. If not, see if there is 12VDC on one of the sides of the solenoid. There are two fuses there… check them.
Loose/corroded connections are the cheapest/easiest things to check/do.
The main power and ground get to the starter directly from the battery. If those terminals are good, then it is the power to the starter solenoid or starter solenoid that is the problem. If you “jump” (a jumper wire goes from the battery lug on the starter (B1) to the solenoid control terminal (B25 RED)) as Dave said, and it turns over, the starter and starter solenoid is good. whew!!
The wire (B25 RED) gets its power from the AUX START SOLENOID. The power wire runs from the starter to the boost solenoid to the isolator and then (B26 RED) down to the AUX START SOLENOID. Putting the boost switch on ensures power to the AUX START SOLENOID from the house batteries.
If you jump (big lug to big lug) the AUX START SOLENOID, the engine should turn over. If it does, try jumping from the terminal with the wire that is from the isolator (B26 RED) to the control terminal (E9 WHITE). If it doesn’t start then it is the AUX START SOLENOID that is bad. If it does, the problem is up the line.
The next item in the line is the N/S (Neutral Switch). If it is not in neutral, no go! Ohh the ATEC black box!
Then it gets its power either from the remote starter and the remote starter circuit breaker (#19) or from the ignition switch.
So, except for bad wiring or connections, it could be:
a bad starter
a bad starter solenoid
a bad aux start solenoid
xmsn not in neutral or bad ATEC computer (I know nothing!)
Do the easy stuff first!!
A heads up on the “hammer fix”.
Usually, when a “hammer fix” is a fix, it is because there is corrosion forming on the commutator under the brushes usually from non-use or a high humidity environment. The corrosion forms under the brushes.
When you try to start the engine, the current can’t flow, or very little of the current can flow, so, no start.
What the hammer does is move the armature, even a teenie weenie bit and the brush sees clean copper and varoom, you’re off and running. Or the brush rubs a little and gets a better contact.
If you are lucky, the odds of sitting on the bad spots (maybe 10 degrees out of 360 degrees circle) or in your favor. Or, after a few more starts, the brushes polished off the corrosion and your problem is gone… for a while.
If it keeps occurring, an emery clothing of the commutator and a move to a better climate, or starting it more often after cleaning will work, or a new starter (worst case scenario).
Having the DW going back there with a hammer every time you leave a campground will give our FT’s a bad name!
I don’t know if this trick would work on our coaches because of the computer check before it allows the power to go to the starter, but, on a car (maybe older ones only), if you turn the key on and off quickly, you might get the starter to just move (rock) a little and get to a clean connection. Then you are on your way. The chance of the starter stopping at the same spot (if it were the problem in the first place) that is corroded is slim. Only if you really, really needed to start (or rain and snow) would the odds of it being on THAT spot would increase dramatically. This would save having to send the DW under the coach in the snow or rain. Michael Baldacchino 1997 40′ U320