Trim switch kills engine

[max366]

Strange problem developed this weekend. 2004 265 Express with T F225 Yamahas.
No problem trimming the engines with the trim switch in the handle, but if I trimmed the starboard engine with the individual switch on the binnacle, the RPMs dropped instantly and would have killed the engine. Let go of the switch, it went back up to the normal RPM and ran perfectly. I have the binnacle wiring diagram but it's hard to see what could be tripping the engine from that switch. Any ideas?

 

[lgusto]

Very low batteries will do this.

 

[max366]

I agree low batteries might do this but why doesn't the same issue occur when trimming the engine using the handle thumb switch or the one on the engine? Volts at 13.8; engines restarts instantly after with it was killed and the starter sounds normal. I suspect the wiring from the binnacle switch might be grounded out. Will disassemble this weekend and check.

 

[VeroWing]

I would suspect a weak ground or bad switch on engine may also be a cause.

 

[Tuna Man]

Just a brief explanation on what may be going on and how to diagnose it. Good voltage (above say 12.8 volts) as measured at batteries. If voltage does not drop below 12.4 at engine when cranked, battery is probably fine. In your case I suspect there is a voltage drop somewhere else. In my experience, I would bet it's a corroded negative wire or connector.