2008 BF 150 Have to hold trim switches to run?

I have a glacier bay cat with twin Honda BF150’s on it. We went out the other day and it ran good until the port motor started suddenly turning off and immediately back on. After fooling with it while we were running we found out it was something with the trim on the throttle handle that was shutting the motor down. Finally the motor shut completely down with no power to the key switch or tilt trim on the throttle and we came in on the starboard motor. After getting it back we checked fuses, connections, battery connections and all checks out and the tilt trim on the motor still works fine.

But we did figure out that if we hold the trim button at the motor and at the throttle the motor starts right up and runs like it should but as soon as we let go of either switch it kills it again and have no lights or power at the key switch.

We did swap the tilt plug from starboard and swapped it to port to make sure the switch was working and it works fine. I’m pretty stumped right now. Hopefully someone can help me. Thanks.

Hi,
One thing I might try is to swap the power trim relays between the two outboards to see if the symptoms follow or remain with the port engine.

Other than something wrong with the relay, I think this could be a grounding problem. It's a common issue on outboards to have corrosion build up at ground points. This can cause weird symptoms to occur.

If the relay swap gives no joy, then I would start disassembling and cleaning all engine grounds starting with the main battery ground cable to engine ground point. Clean and shiny connections are MANDATORY.

Test for function after each "scrubbing" with a wire brush.

There is a ground "cluster" for the 5 ground wires from the ECM (two dark green, one brown, one white with green stripes, one white with black stripes,) there is also a black ground wire from the ignition and kill switch for a total of 6 wires. Clean them all.

There are also ground points for the starter and alternator.

All ground points need cleaning occasionally so even if this doesn't solve the issue don't consider it a futile exercise. It's "electrics 101" and will at least be something to check off the to do list.

Forgot to mention that there may also be a ground for trim relay near where it mounts. I'm looking at a wiring diagram on the Honda power equipment web page but it doesn't list exact locations for the frame grounds

I also think that you may want to consider simply unplugging some electrical connections, cleaning the contacts with a product like DEOXIT spray, carefully inspect each pin and receptacle and carefully, CAUTIOUSLY, plug back in. You don't want your efforts being the reason a pin gets bent or a receptacle gets pushed so deep into it's socket that good contact is lost. Happens more than you might think.

Over time, engine vibration can cause wear to occur to the sockets and connector pins. The connections get loose because of this and lose their "drag fit" to one another. Once loose it's easier for corrosion to get a foothold in the voids. This is especially true with the larger group connectors like ECM and main relay because of the number of wires hanging. More wires mean more leverage against the connector to facilitate movements.

Good luck.