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  1. #1
    Petty Officer 2nd Class
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    May 2009
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    Default My trim gauge doesnt work!

    Good morning!!

    1989 Mercruiser 5.0 LX Alpha One OC507398

    Having previously rebuilt my trim limit switch and got my trim system working top notch, I moved onto my trim indication system.

    I found the two wires coming out of the sending unit broken and frayed so I disassemble the sending, repaired, soldered and shrinkwrapped the wires and cleaned all of the crap out of the unit. Then I reconnected it. My gauge at the dash reads full scale up regardless of the postition of the outdrive. I have even removed the sender from the outdrive and manipulated the cog on the outside of the sender to get any response. Any ideas??

    Thanks!!

  2. #2
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: My trim gauge doesnt work!

    Have you checked the sender with an ohm meter to see if it's doing anything? If not, it's time to replace them both. they come as a kit with both the gauge sender and TL switch.
    Don S.


    Please, no PM's (Private Messages) regarding boat/engine problems.
    That is what the forums are for.
    Only forum/moderator issues will be answered in PM's.

  3. #3
    Petty Officer 1st Class series60's Avatar
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    Default Re: My trim gauge doesnt work!

    Quote Originally Posted by YN2(SS) View Post
    Good morning!!

    1989 Mercruiser 5.0 LX Alpha One OC507398

    Having previously rebuilt my trim limit switch and got my trim system working top notch, I moved onto my trim indication system.

    I found the two wires coming out of the sending unit broken and frayed so I disassemble the sending, repaired, soldered and shrinkwrapped the wires and cleaned all of the crap out of the unit. Then I reconnected it. My gauge at the dash reads full scale up regardless of the postition of the outdrive. I have even removed the sender from the outdrive and manipulated the cog on the outside of the sender to get any response. Any ideas??

    Thanks!!
    Did you remove the trim indicator sending unit and wires from the boat? If the wires were frayed outside you can bet they are frayed inside the boat also. Did you re-install the sending unit via the manual? Many times these units can be problematic. It is always best to trim by feel. Feel the boat underway as you trim up and down. Speed and ride are better indicators for best trim settings. My trim gauge and sender work perfect but I never look at it. I drive by feel.
    1984 IMP X215SC
    Mercruiser 305/Alpha1 upper R lower
    Off forum site of rebuild
    - from acquisition - demolition - reconstruction - splash

    1970 MirroCraft 14' tinny/1979 Evinrude 25 long shaft electric start.
    Spare: 1959 Evinrude 18 short shaft electric start.

    Bill

  4. #4
    Petty Officer 2nd Class
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    Default Re: My trim gauge doesnt work!

    OK, here is what I have found.

    I disconnected the trim sending unit from the outdrive so it is dangling and then traced the wires inside to a plastic "junction box" where they are each individually connected to other wires. I checked the continuity of each wire from the unit to the end of the wire inside the boat and the continuity was good and there is no short from one wire to the other. I checked the full length of the wires inside and out and the insulation is in surprisingly good condition.

    Then I attached the ends of the wires to an ohmmeter and rotated the cog on the sending unit by hand and the ohms range from 0-70. So at this point I believe the repairs are good and the trim indication sending unit is repaired.

    What indications should I have on the wires on the "junction box" at the motor. This is right by the circuit breaker for the starter above the water seperator filter. Does one have voltage coming in? The other go to the gauge? I have read on other threads that the trim sending unit acts as a potentometer (sp) sending varying voltage to the gauge.

    Is there a wiring diagram available somewhere? My SELOC manual (I know, not the best) doesnt have one.

    Thanks all!!

  5. #5
    Petty Officer 1st Class
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    Sep 2010
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    Vermont
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    Default Re: My trim gauge doesnt work!

    You should read this at the engine junction box and at the gauge ( WITH VOLTAGE OFF AND THE GAGE DISCONNECTED ) trim gauge 10 ohm Down, 167 ohm Up --

    If that checks out unsure you have 12 volts to the gauge when power is on / you also need a good ground on the 2nd wire that does not go to the gauge to complete the ckt.

    If the 12 volts is present on the input to the trim gauge you can ground the output siide that goes to the sender to verify the gauge works correctly.

    I am assuming the gauge worked ok at one time -- but I will mention just in case that the gauge must be Merc compatible as some other brands ( Yamaha etc ) use differing resistance values & gauge designs change accordingly.

  6. #6
    Petty Officer 1st Class series60's Avatar
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    Default Re: My trim gauge doesnt work!

    Quote Originally Posted by YN2(SS) View Post
    OK, here is what I have found.

    I disconnected the trim sending unit from the outdrive so it is dangling and then traced the wires inside to a plastic "junction box" where they are each individually connected to other wires. I checked the continuity of each wire from the unit to the end of the wire inside the boat and the continuity was good and there is no short from one wire to the other. I checked the full length of the wires inside and out and the insulation is in surprisingly good condition.

    Then I attached the ends of the wires to an ohmmeter and rotated the cog on the sending unit by hand and the ohms range from 0-70. So at this point I believe the repairs are good and the trim indication sending unit is repaired.

    What indications should I have on the wires on the "junction box" at the motor. This is right by the circuit breaker for the starter above the water seperator filter. Does one have voltage coming in? The other go to the gauge? I have read on other threads that the trim sending unit acts as a potentometer (sp) sending varying voltage to the gauge.
    This is all good!

    Is there a wiring diagram available somewhere?
    Yes but Bond-o or Don can probably get to it before I can.

    My SELOC manual
    1984 IMP X215SC
    Mercruiser 305/Alpha1 upper R lower
    Off forum site of rebuild
    - from acquisition - demolition - reconstruction - splash

    1970 MirroCraft 14' tinny/1979 Evinrude 25 long shaft electric start.
    Spare: 1959 Evinrude 18 short shaft electric start.

    Bill

  7. #7
    Moderator achris's Avatar
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    I come from a land down-under...Perth, Australia
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    15,186

    Default Re: My trim gauge doesnt work!

    Quote Originally Posted by YN2(SS) View Post
    Is there a wiring diagram available somewhere? My SELOC manual (I know, not the best) doesnt have one.

    Thanks all!!
    You are going to want to download these....

    Engine manual -> https://docs.google.com/open?id=0B1T...VNLbWdZMTRQTkE
    Drive manual -> https://docs.google.com/open?id=0B1T...YTkwcUh5RElUQQ

    I just hate seeing people using seloc (or any other non factory) manual...

    You'll find the wiring for the engine end on page 4F-2 and for the dash end on page 4F-6 of the engine manual.

    Chris.........

  8. #8
    Petty Officer 2nd Class
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    Default Re: My trim gauge doesnt work!

    Im going to go through the engine side of the wiring harness. I have good ohm readings at the junction box. Nothing at the gauge, But I do have continuity from the boat side harness plug (male) to the gauge (a white wire with purple stripe). I have 12 v to the gauge, and a good ground too.

    So, somewhere between the junction box on the engine and the. female side of the engine harness, Ive got a problem. Im gonna check out the wiring diagrams.

  9. #9
    Petty Officer 2nd Class
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    Default Re: My trim gauge doesnt work!

    Ok, would you believe in the last 23 years of this boats life, some POS (previous owner (sailor)) has jacked around with the wiring harness on the engine??????

    So I downloaded the files above (Thank You achris Very Much!) and printed out the two diagrams he mentioned. Off to the boat I went with my multimeter, diagrams and scissors to carefully cut tape.

    Low and behold, with the trim sender disconnected, both wires going to the harness were grounded. One should have been. The other, not so much. Matter of fact, it should have had continuitiy to the #10 hole on the female (engine) side of the engine harness. So I unwrapped tape all over the place and found that the wire that was grounded actually was one of two ends of a wire that are supposed to go to the audio warning system (the wire came from the harness plug and went to an oil pressure sender and the trim sender (Wrong!!). It was suppossed to go to a temp sender. I found the end of the wire that is supposed to go the the trim sender junction box routed to the aft end of the engine and taped off next to the ignition coil. UGGGGGGHHHHHHHHHH!

    Now, I think I know why there is an extra wire routed from that temp sender up to the dash.

    Lets see where that problem leads. But the audio warning system doesnt work. Next thread.

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