Tilt/Trim Unit - 2 wire vs. 3 wire?

[Mark9740]

I've got an 85HP Force and looking for a tilt/trim unit for it on Ebay. Can anyone tell me what the difference is between a 2 wire unit and a 3 wire unit? I see both kinds for sale. Does one work better than the other?

Thanks

 

[Frank Acampora]

Re: Tilt/Trim Unit - 2 wire vs. 3 wire?

Three wire unit has a cast aluminum reservoir, a small motor, and full power is passed through the trim switch. A separate ground wire passes to the battery and the switch wires ar (I think) #10 gauge. The motor has field coil windings and a bi-metal overheat current interrupter switch built in.

Two wire unit has a larger plastic reservoir, a larger motor, and uses relays to power the motor. Only signal current passes through the trim switch. Because of this, 16 or even 18 gauge wire can be used from switch to relays. The field is two semi-circular permanent magnets. It uses (sometimes) an external 30 amp circuit breaker.

The three wire motor can, with a little thought and creativity be converted to relay use, but the two wire unit MUST be powered with relays.

I have both types on various engines and I really prefer the two wire system although the three wire system works well too. It is just personal preference. However, due to the large wires and high current at the switch, I would pay less for a three wire system.

They do have slightly different pumps, but for that you need to wait for RRitt to reply. I do not know the particulars of the pumps.

 

[Mark9740]

Re: Tilt/Trim Unit - 2 wire vs. 3 wire?

Thanks for the education Frank!

 

[RRitt]

Re: Tilt/Trim Unit - 2 wire vs. 3 wire?

1989-1992 2 wire with round pump motor is the best.

The 1991-1994 2w with squareish pump would have been the best except that Mercury got cheap on fluid and ruined some of them. If you get one of the units with cheap ATF then failure is both catastrophic and emminent. Buying a system with square pump is a high-risk venture. There is no way of telling if mercury used the cheap fluid or not until it breaks. If it is cheap fluid then it is only a matter of time before you need complete major obverhaul of trim system. But hey, on the bright side - mercury made at least an extra 10-15 cents of profit per engine and the failure is well after warranty expires. Win-win for mercury.

Before mercury, the systems used non-detergent oil and have a much longer life-span. 30 years is common for rams. 20 for pump. Look for a pump with allen key release plugs near to where the oil lines connect. That will be the best overall balance between performance, durability, and cost of ownership including potential repairs.