Re: Weak Power
It would help if we knew exactly what engine you're speaking of.
First, disconnect the electric fuel gauge completely and return the rig's electrical system to its original pre-operation condition pertaining to the wiring. This would be the trouble shooting start point.
New batteries can be faulty (it happens). make sure it has a full charge.
Remove and clean "all" cables, battery terminals, starter solenoid, ground, etc etc. They may look tight, may be tight, BUT many times cables are tight but have a dirty corrosive connection that results in a voltage drop.
Also, after attempting to crank the engine for 15 or 20 seconds, check the cables for hot spots which could reveal a internal (corroded) flaw of the cable. The area which is most hot would be the damaged area.
When the power is as it should be, then go back to the fuel gauge installation project, otherwise you may be trying to correct two problems at the same time which can result in much confusion.
A faulty rectifier would result in absolutely no functioning of the tachometer. A failing regulator could cause an erratic tachometer operation. If the engine will run, a test of the tachometer and regulator can be performed as follows (assuming the engine has a water cooled regulator/rectifier assembly).
(Testing Tachometer With Water Cooled Regulator/Rectifier)
(J. Reeves)
A quick check is to simply plug in a another new tachometer as a piece of test equipment. If the new tach works properly and the old tach didn't, obviously the old tach is faulty.... but usually boaters don't carry around a spare tach (see below).
A faulty rectifier wouldn't damage the tachometer, the tachometer simply wouldn't work. This is due to the fact that the tachometer operates off of the charging system and the rectifier converts AC voltage to DC voltage, enabling the charging system. A faulty rectifier disables the charging system, and the tachometer simply doesn't register.
However.... those water cooled regulator/rectifiers that are used on the 35 ampere charging systems (and some others) bring into play a different type problem, and as you've probably found out, they are really a pain to troubleshoot via the proper procedure. There's an easier way.
The tachometer sending/receiving setup operates off of the gray wire at the tachometer. That same gray wire exists at the engine wiring harness which is connected to the engine electrical terminal strip. You'll see that there is a gray wire leading from the regulator/rectifier to that terminal strip, and that there is another gray wire attached to it. That other gray wire is the wire leading to the tachometer which is the one you're looking for.
Remove that gray wire that leads to the tachometer. Now, find the two (2) yellow wires leading from the stator to that terminal strip. Hopefully one of them is either yellow/gray or is connected to a yellow/gray wire at the terminal strip. If so, connect the gray wire you removed previously to that yellow/gray terminal. Start the engine and check the tachometers operation, and if the tachometer operates as it should, then the regulator/rectifier is faulty and will require replacing. If the tachometer is still faulty, replace the tachometer.
If neither of the yellow wires from the stator is yellow/gray, and neither is attached to a yellow/gray wire, then attach that gray tachometer wire to either yellow stator wire, then the other yellow wire, checking the tachometer operation on both connections.
I've found this method to be a quick and efficient way of finding out which component is faulty.... the tachometer or the regulator/rectifier. It sounds drawn out but really only takes a very short time to run through. If the water cooled regulator/rectifier proves to be faulty, don't put off replacing it as they have been known to catch on fire with disastrous consequences.
