1992 Mariner Magnum 40 started trying to fix tach... can't tell what's going on

was hooking up a tach i've used in the past to check my rpm vs my prop. checking to see if i had an over rev limp mode issue last time i had the boat out, or if it's something else

I have a tach i rigged a pigtail for long ago to the ignition switch box... so when i want to test, i just plug it in to the pigtail.

when i did my test... tach wouldn't leave 0. checked with manufacturer... and they said i should see at least 3.5 ac across the grnd to send posts. i get like .59 v ac. (ign to ground post gives me the correct 12+ v dc)

went to the rectifier and tested from ground to both yellow posts. one is giving about .59v ac... the other about 29 v ac.

the engine starts fine, and when i rev it and check at the battery, the voltage comes up at the battery... so i think it's charging.

mechanic's not local... but he gave me some time on the phone. he indicated the mismatch of the power on the two yellow leads would seem to say the stator has got a problem.... but from my youtube watching, etc... i'd think i should either have a starting or a charging problem.

i considered swapping my grey tach sender wire to the higher voltage yellow post.. but he said that he'd guess that would smoke the tach.

i was considering pulling the yellow stator leads off the rectifier, running the engine, and seeing if my values remain the same for voltage... but i want to confirm that's safe to do (and now thinking about it... while i wouldn't worry about not charging the batteyr... wondering if it doesn't kill the ignition circuit)

ah. fun old boats..

I suspect your regulator is shot.

Try using one of the yellow wires off the stator. And if that doesn't work right, try the other yellow wire. (I've seen where one will work, the other will not!)


If the tach now functions, replace the voltage regulator.

Jeff

Do you mean rectifier? (not sure if these units had a combo rectifier regulator). i've got a black stator... so don't think i have a separate regulator.

If your rectifier looks like below is a rect/reg combo. This is the new updated one from Merc

mine looks like this. black stator and three post rectifier

after trying to order a replacement from 'Zon (got shipped an empty, open bubble wrap mailer...) I found a bone yard in Green Bay who had pull-offs. Picked up two to have a spare. One isn't working... other tested fine.
Slapped it on motor... Tach works now... and screwed up voltages on the stator posts have evened out. Gonna order a new replacement for a spare and call 'er good.
(Happy i don't have to do a stator replace as well... that's worth more than the motor is)

now i'm trying to confirm my tach is reading the correct rpm. have talked to the techs, and they told me how to read the signal on the sender with a multimeter reading ac frequency. trick now is.. .i think my crappy multimeter isn't right. he said i should see values like 100 hz - 560 hz... and i'm seeing values of 2.4-3.9 kHz. the tach looks like it's working... but i'm just trying to make sure it's right as it's at 5600 rpm for WOT... when it should be at 5500 (and to my ear... it doesn't sound "wrong." like when you cavitate or something that lets it spin.

another update..., usoing a better multimeter, fluke 117... easy peasy... i get nice Hz measurements of 60-560Hz. This signal uses a simple multiplier of 10... so 60=600, 560=5600rpm, etc. I dicked around calibrating the tach...not an easy task as the adjuster doesn't have a lot of granularity... figured out if you think you've got it to 50 rpm or less within target... stop there... call it good. you'll spend all day dicking with it trying to find a sweet spot.
after doing this... i'm more likely just to hook up a fluke as it's just easier, and more precise.
on to nailing down what i want to do for a prop