Suzuki trim switch failure caused fire?

[18pontoon]

I bought a 1998 DF70 off ebay at a great price with wiring harness damage due to a fire. I have been rebuilding the damaged parts of the harness and got to the point of testing the wiring prior to installing new relays for the PTT system.

Turns out the PTT switch on the side of the motor was broken in a way that caused the common lead (middle) to be connected to both the up and down control contacts. Unfortunately it seems the 1998 ECM is not smart enough to detect this as an invalid state, and the ECM energized both control wires to the PTT relays most likely causing the fire. Both relays engaged would attempt to drive the PTT motor in both directions (direct short 12V to ground).

Is this a common problem? Is this issue fixed on newer model ECMs? The switch innards look awfully fragile.

[18pontoon]

I think I interpreted the schematic incorrectly... If both up and down switch contacts are closed, all it will do is activate both relays putting +12V on both PTT motor contacts. The motor won't move as there is no potential difference between the leads, but more importantly it won't start a fire as there is no unfused short to ground.

Seems then the fire was caused by one of the relays being rusted out and the relay terminals making contact from bouncing around.

Good to know its not a major design flaw

[Moonlighter]

Glad that you figured it out and reported back. These things sometimes take 2 or 3 looks at the wiring diagram to understand what is happening and the solution.

Best of luck with finishing the project and getting her on the water again!

[jHydroman]

On one of my DF 140's I had one of the trim switches on the engine short out only on the raise contacts while fishing in the shipping lanes in the Straights of Juan de Fuca. I had the trim selctor sw in the positon that both engine trims functioned with the operation of either trim sw.

This caused both engine to tilt up to the full up position and both propellers were completely out of the water and both trim motors running continiously.

In an effort to get underway I opened the by-pass on engine and they both lower and I was able to get clear of the ship channel.

I found that the port engine trim sw. locater on the engine was full of water, causing it to short out. If i had known at the time that this was the problem, I could have just repositioned the selector switch at the helm and only the port engine would have been affected.

Jim

[18pontoon]

Thanks for the replies.

This motor is a $700 ebay special that just increased its value to ~$3000 after I finished the wiring repairs and got it running last night . I have a 18' pontoon with a DF50 on it now. Planning swap motors and put this DF70 on this weekend or sometime next week.