3-wire Calco to 2-wire Prestolite stringer

[Hackster]

Howdy... Couple years ago the Calco tilt/trim pump on my 1978 Evinrude 115 went south. I bought a used Prestolite 2-wire stringer pump off ebay, but then work and other stuff made it necessary to mothball my boat for an extended period before I ever got the Prestolite pump installed. So, fast forward a couple years, I installed the Prestolite pump today, but it's not working (motor no spin). I know the original setup uses the solenoid for the up switch and straight voltage for the down switch. I've seen posts about using a two-relay setup for a two-wire pump, but is this a requirement, or did I buy a bum pump? Checking the wiring at the transom with a DVM, both of the original red and blue wires (which formerly fed the Calco) show 14 VDC with the meter's +lead connected and the -lead grounded to the motor when the respective up and down buttons are pressed (and the up button makes a very loud solenoid click). The Prestolite has one blue wire and one white wire (I know the ground goes through the frame). I even added an extra ground wire from the pump mounting bolt to the motor. But with the original red tied to the Prestolite white, and the original blue tied to the Prestolite blue, no motor action at all (and I tried it opposite as well).
So, to simplify the question- should the Prestolite be working with the single solenoid setup, or am I missing something, and need to install the dual-relay setup? Or did I let the "new" used Prestolite pump sit idle too long and it lost interest? Any thoughts much appreciated.
-John

 

[Hackster]

The Prestolite model number is HYB-5008, if it makes any difference.

 

[Chris1956]

Two wire pumps are not grounded thru their frames. To see if your pump works, put +12VDC on one wire, and -12VDC on the other wire and see if she spins. If so, note the direction of the spin. Now reverse the wires and the motor should spin the other way.

If the motor spins, you can use it, but you will need two relays. Solenoids and relays are different. Relays provide either +12VDC power when energized or -12VDC (ground) when not energized. Solenoids provide power (energized) and nothing when not energized. Obviously, your two wire motor will not spin, if the negative wire is open.

 

[Hackster]

Thanks, that's the most concise description of the difference I've seen. Bad news is the motor must be toast, because when I hook up both wires to 12V and ground, the motor doesn't spin, and the wire attached to ground gets hot, fast. :blue: