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Yamaha 115's not cranking, need good brains to solve this one

Kaimana

New member
I read all the threads and posts before posting this; thanks everyone for all the good experience and recommendations! Couldn't find anything similar on the forum.

I've got something really weird happening. FWIW, I've been a diesel mechanic since 1976, always rebuilt my own pickup truck engines, carbs, fuel injection, diesels, what have you. I graduated to outboards a couple years ago, and so on. So I've got some chops. But this one's got me stumped:

Problem:

Trying to start Yamaha 2007 4-stroke F115TXR’s after a 3-month layup (inside a building with cover on); and they won’t crank. They started and ran fine before. Using the same cables, key switch, fuel tank, and fuel, non-ethanol gas.

Symptoms and diagnostics:

1. The motors don’t crank from key switch, but with switch in the on position, I get a fuel pump noise for about 3 seconds, then it stops. Conclusion: The “Motor Run” circuit wire and associated part of key switch is OK, but starter doesn’t work.

2. I pop off the tilt-trim relay to get to the starter solenoid wire connection behind it (brown wire), disconnect it from the engine wiring harness, and energize the starter solenoid, and they crank. Conclusion: starter solenoid and starter both OK. I reconnect the brown wire and put the tilt-trim relay back.

3. I unplug the main wiring harness from the key switch at the motor end, and short from the red wire to the brown wire (starter solenoid) inside the plug coming out of the motor, and they crank. Conclusion: Brown wire is OK between the motor plug and the solenoid. NO fuses blown by this test; just wait. I plug main wiring harness back into motor.

4. With the main wiring harness unplugged at the key switch end, I short from the brown wire to the red wire (12V+) on the key switch end, and hear a little noise from the motor, but the starter doesn’t crank. The little noise is the upper 20A fuse under the yellow cover blowing. I look at the T115TR wiring diagram I have, and determine that it’s the fuse that protects the 12V+ circuit going to both the tilt/trim relay and the key switch. BTW, tilt-trim switches on throttles and side of engine cowling both work, don't blow that same fuse. I put a new fuse in. It seems this harness has an internal short, but just wait.

5. I plug the key switch end of the harness into the key switch, and turn the key to the on position; I hear the fuel pump noise again. I turn past the on position to the start position and hear a little noise from the motor, but the starter doesn’t crank. The little noise is the 20A fuse blowing, again. I put a new fuse in.

6. With a new fuse in, I turn the key on (but NOT to the start position), and short the two starter solenoid terminals together to start the motor. It runs fine, and turns off when the key is turned off. No fuses blow. So the motor side of everything is OK.

7. I unplug the key switch and test continuity with a Klein CL800 meter, and everything acts clean. I check the brown wire (starter solenoid) against black (ground) when the key is turned to start, to make sure it is not shorting to ground inside the switch when I try to start, and blowing the fuse; there is no connection. With the key held in the "start" position, I check from EACH of the other terminals involved: red (12V+), yellow (to motor "run" circuit), and brown (to starter solenoid relay) to ALL the other terminals in the switch, to confirm there's no internal shorts happening: and find none. It seems I confirmed the switch is OK.

The only thing I don’t do is run current through the switch: I tried to think how an electrical circuit could show as open but would short to another circuit when power was applied (and blow the little 20A yellow fuse), and my mind couldn’t make it make sense.

8. I try this with two different wiring harnesses from two Yamaha T60 TLR's I also have, which was running before I stored them, and those wiring harnesses were likewise in storage. I also tried it with the two original wiring harnesses from the two 115’s; they all produce the same result. So I’ve tried four different main wiring harnesses, and have gone through a few boxes of the little yellow 20A fuses by now.

Until I tested the key switch I thought it was the switch; I mean, how can 4 wiring harnesses, even if they are old, produce the same symptom? In all fairness, ALL the wiring harnesses are old, two of them had visible (copper-green) corrosion on the inside terminals on both the motor and key switch ends that I cleaned off with a miniature wire brush before connecting them. They were all working before; could they all have gone bad sitting in a box in the shop for 3 months?

Do I buy two new harnesses at $110 each, and/or two switches at $150 each, just to try out, even though I’m not certain what the problem is? I’m stumped!

I'd be happy to have a "best-guess" from a Yamaha outboard old hand on the forum who has more experience with these than I have. No shame no blame if it doesn't work, I'm going to spend more money and time fixing it one way or another.

Thanks!

With Warm Aloha, Tim
 
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