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Tan
Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10665
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Tan, how can i determine if I have a bad power trim

Customer Question

Tan, how can i determine if I have a bad power trim indicator. When I read 136 ohms at full down, and 35 ohms at full up. These readings were taken at the leads coming through the stern, and at the indicator inputs. Upon operating the stern unit it reads
only full up regardless of the actual position. The indicator reads off scale high when powered off. When powered on it reads full up. Do these indicators fail and if so what is the failure signature? Thx- Marshall
Submitted: 1 year ago.
Category: Boat
Expert:  Tan replied 1 year ago.
Hi Marshall. Take the ohm readings at the trim gauge when disconnected from the gauge. Are the readings the same when raising and lowering the drive?
Customer: replied 1 year ago.
The 136 ohm reading is when full down, and the 36 ohm full up reading is 136 ohms when full down, and when operating the trim function the readings transitions with the stern drive.
Expert:  Tan replied 1 year ago.
Did you have the trim sender removed?
Customer: replied 1 year ago.
NO, these readings are from the trim sender, at the trim sender, and at the indicator input posts. Sensor post and the ground post. So in all, I have the same readings at the trim sender,and the wire harness, and finally at the indicator post connections. All points are same or so close as to not be a concern.
Expert:  Tan replied 1 year ago.
Ok the sender should read zero in the full down position and up to 160 in the full up position. The sender is bad. Do this test for the gauge ground the sender terminal does the gauge peg with key on?
Expert:  Tan replied 1 year ago.
Here is the test out of the manual.Trim Position Sender Testing1. Disconnect the indicator leads from theterminal block on the harness plug bracket.2. Connect an ohmmeter to the disconnectedleads.3. Start with the unit in a down position and trimthrough the total travel range, watching the meter.It should show a smooth progression from zerothrough 80 ohms (dual station sender) or 160 ohms(single station sender).4.If the meter needle does not move or if it moveserratically, remove the sender and repeat the test. Iferratic or no movement is still noted with thesender off the gimbal ring, replace the sender.
Expert:  Tan replied 1 year ago.
What did you find Marshall?
Customer: replied 1 year ago.
tan, I have found that at the sender, full down reads 0.6 ohms and full up reads 96 ohms. The wire harness at the indicator reads, 0.5 ohms, and at full down reads 95 ohms. Transition is not smooth. If the sender is the problem, the sending parts appear to be easily replaced without removing the pivot shaft. I have removed the complete sending unit and just let it hang whille I cleaned the grease from the contact area. Just what is it that goes bad on these senders that I must remove the drive section? The the wire harness is a mess. but that can be easily taken care of after I correct the actual problem. THX- Marshall
Expert:  Tan replied 1 year ago.
The drive doesn't have to be removed to replace the sender. Ok the sending unit is bad as it isn't reading through the full range. The sender itself is not repairable it has to be replaced. So replace the sender and straighten out the wires. That should fix the issue.

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