20 amp fuse keeps blowing.

[Striddy56]

Have a 2000 150 VMax on my Maverick MA 18.5. All of a sudden I've started blowing the 20 amp fuse on port side of engine. I can't tell when it happens but it's located next to the 30 amp fuse and they both run next to the trim switch. I replace the fuse and able to work the power trim up and down continuously, run the motor, and shut it down for the night, but when I do the same several days later, it's dead and fuse is blown. The only 3 three steps I do are, turn the battery switch on, run the engine, and run the trim up/down, shut the motor off, and turn battery switch to off. I don't know where to start on looking for a short, all connections appear to be solid. Any ideas would surely help in my brainstorming.

[rodbolt17]

bust out a service manual.
locate what circuits are feed by said fuse.
find the short to ground.

[rodbolt17]

the trim motor is NOT fed by a 20 amp fuse.
that would be the 60/80 amp main.
the 20 amp is for control circuits.

[Striddy56]

Control circuits meaning what?

[boscoe99]

Control circuits meaning what?

A control circuit is used when small wires carrying small amounts of current are used to control big honkin wires carrying lots of current. In the case of the power trim system small wires run from the trim switches to the trim and tilt relay. Then big wires run from the relay to the trim and tilt motor. The small wires are considered to be the control circuit. They control the ptt relay.

[boscoe99]

The red wire connected to the 20 amp fuse runs to the ten pin engine harness connector, over to the ten pin harness in the boat, and then up to the control box from where it connects to the key switch and the throttle handle trim switch. It may also connect to certain gauges. While on the engine harness it connects to the lower cowl mounted trim switch.

Somewhere along the way something might have chafed the red wire to ground. When the wire contacts a ground the fuse will blow as it is intended to do.

Now the red wire also connects to a yellow wire when the key switch is on. If the yellow wire chafes to ground the same thing will happen. The fuse will blow.

If and when the trim switch button is pressed a sky blue or grass green wire gets power from the red wire. Same thing with those wires. If grounded the fuse will blow. Thar she blows.

[throrope]

Don't forget ground connections. A bad connection creates a voltage drop then amps go up and potentially cause a fuse to do its job. Ground connections are a bugger because they are often the last checked and least expensive to fix. Or put another way, solved after spending money fixing what wasn't broke.