I have a 1999 Formula 400 ss with twin 502 MPI's. There are three batteries, one is connected to right motor with an on off switch. The other two are connected together and run to the port motor on off switch, then on to the house switch. There is an emergency tie in switch if either goes dead. My understanding is that these should be separate, i.e. if the right switch is on, the right motor should start. When I turn the left switch on, ignition is completely dead on the left motor. If i try to start the right, I hear a click, but nothing else (doesn't sound loud enough to be the starter clicking). Same on the other side. I have to have all three switches on (right, left, and house) to start the engines. Was this normal?

I checked with a multimeter. I had the left engine running and the alternator only showed 12.2 at 2k RPM's. The alternator is brand new. The left battery read 13.0 volts. Now this is what really surprised me. I checked the alternator of the right engine (not running) and it showed 13.2 volts! What the heck is going on? Did they hook the alternators together in parallel somewhere and I just can't find it? There is only one voltmeter on the dash. The last time I ran it it showed 16volts, so i figured it was broken. Today while testing it doesn't register anything. I'm kinda stumped at this point. Based on the wiring diagram for these engines everything looks to be set up correctly.

Phil

UPDATE. With the left battery on and the right off, when I turn the ignition key to on, the left fuel and water temp gauges are dead. However when I turn the right ignition key on, the right fuel and temp gauges come alive. It is the exact opposite with the right battery on and the left battery off. If I have both battery switches on, then the ignition keys work correctly for each side.

you have stuff cross-connected. and it sounds like left alt isn't hooked to anything and right alt charges everything.

Yes I finally found that the power wires running to the ignition breakers were crossed. This solved the battery switch problem. However I'm still getting the same readings when I check the alternators. With just the port running it shows 12.2 at the alternator and 13.0 at the port battery. With the strb engine off the alternator reads 13.2. If I have them both running it is the same. The strb battery bank is not getting any charge, showing only 12.2-12.4 at best. I've traced just about everything I can (or know about). Are there any other tests or checks I can do to the system to track this down?

put voltmeter on big wire on back of alternators when running. u should see around 13.8 to 14.5. they could be bad, they could just not be being turned on by the boat.

Test like Derek suggested but make sure only one motor is running at a time. Also bring the motors up to 2000k rpm for 15 seconds or so then back to idle before you test. Some alternators dont kick in till you have revved them up a little.

Chris

check the big dia wire coming off the alt,i had one that broke the ring terminal in the rubber protector and you could not see that it was broke until the rubber was pushed out of the way to remove the nut on the alt lug.

If this is a Merc setup there should be a purple wire on the back of each alternator. This wire is the ignition turn on for the alternator. Make sure you're getting key voltage there, of not the alternator won't "turn on" ....so to speak.

Good luck!

i have checked the voltage from the big wire with only one engine running. That's where i discovered the issue, and can't figure out how the port motor is showing 12.2 from the wire while running and the strb motor is off but reading 13.2 from the wire. I'm thinking they are tied together somewhere, otherwise how could i only have one volt meter on the dash?

I will check the purple wires today, I didn't think of that. Thanks for all the replies, this has been trying on my patience to say the least. I've not been to Put in Bay one time this summer!!!!

How'd you make out?