1992 240Z voltage drop at dash

wolfe1 · 05-26-2010, 03:15 PM

Hello everyone. I'm new to the forum looking for some help. I've got a 92 Mariah Z240 with a 7.4L Merc motor. I have an electrical issue involving a voltage drop at the dash.

I've just installed a new battery and have 12.3V at the posts. With the engine off and the ignition on I only see 10.5V on the volt gauge mounted in the dash. With the engine running, and all accessories off, the voltage does come up to over 13V. The voltage at idle does not stay constant, it flickers for lack of a better term, as if there it an itermitent drain. When I switch on the blower the voltage drops below 12V, as I turn on other things such as lights, docking lights and others, the votage drops below 10V. I've even had the motor shut down at idle before with the voltage at the gauge this low.

I've been dealing with the problem for years and after some resent issues I'm determined to find the cause. My thoughts are loose or poor grounds and possible loose spade connectors behind the dash creating resistance and power loss. I've had the alternator tested and it's fine, and as I mentioned the battery is new. Any help would be appreciated. Thanks, John

IowaWing · 05-26-2010, 08:18 PM

I had the same problem with a '95 chevy 1 ton dually. I repaired it by replacing the engine to frame ground cable.

With that in mind, I would closely check the ground wires. I would check the engine to battery connection first and then progressively move to the lighter weight wires. A volt meter would help pinpoint the poor connection as you would see a voltage reading across the connection. You might have to turn some of the loads on before you find the bad connection. It sounds like one of the primary connections since it seems to affect everything including the ignition.

I used a battery jumper cable to jumper each of the wires and their connection points until I found the bad one. Maybe using that hint will help you find your bad connection too.

Let us know what you find.

spinks99 · 05-27-2010, 02:20 AM

Hey Wolfe,

I just bought my Mariah last fall so I haven't been able to go through the whole thing yet, but I have noticed a lot of bare connections. Everything is labeled nice from the factory, but it appears that they tried to use some type of quick-couple connections. These connections are very poor and not a good idea from the factory. These connections should be fitted with compression type, or butt connectors for a good, tight, clean fit. Look for those things and get rid of them.

It also looks like these connections were covered with a rubber sleeve, that in many cases has slid away from the connection leaving them bare. Hot leads and grounded leads touching intermittently could be causing your problem.

The other thing I found was a buss-fuse block right under the steering wheel. This is separate from your circuit breakers (if you have them). Check out whats going on there. You may find something loose or a buss fuse going bad. I lost my hatch and seat operation from a bad buss fuse. It wasn't blown it just wouldn't conduct and juice.

Danny

wolfe1 · 05-27-2010, 01:43 PM

Thanks for the replys. I took another look yesterday. I pulled off all of the terminal connections and cleaned and recrimped all of them throughout the dash. I didn't really see and corrosion or find suspect loose connections. After doing that, I had no change in the voltage drop. I've been using the connection at the blower switch as a starting point because it seems like it pulls the biggest load from the dash. I see 12.34V at the blower switch (same reading as directly off battery) with it off and about and about 11.5V with it on. I see a drop at the battery from 12.34 to 12.24 with the blower off, and then on. Would you guys consider that normal? I would think it's normal to see a progressive drop in line voltage as load increases on the circuit. This was all done with the motor off.

Also, my drop at the dash isn't as bad as originally thought. Turns out my dash mounted volt gauge reads 1V low from actual. At this point I'm not even sure I have a problem, now that I know the gauge reads low. I've owned the boat since '96 and it's always been this way. What prompted me to mess with it at this point was I installed a radio that shuts down when the voltage gets low (I believe 10.5-11V). I hooked it to power under dash. I think I'm going to run a line straight to the battery and see if that solves the problem.

Can any of you first gen Mariah owners out there confirm if you see a drop in voltage on the dash mounted gauge as you turn on accessories? The blower and docking lights seem to be the big ones. Thanks for all the input. John

IowaWing · 05-27-2010, 04:20 PM

With engine running, the voltage at the gauge should be approximately 14 Volts if everything is OK.

Since you saw voltage dropping to the 10 volt range, it is likely you still do have a problem with a ground connection.

On the truck I was talking about, the battery would stay charged but when I turned the lights on, the indicated voltage on the dash gauge would drop to below 10 volts and the engine would die due to the drop in voltage. It was cured when I replaced the engine to chassis ground. Take a heavy wire (like a battery jumper cable) and go from the battery to the ground connections and see if jumping one of the wire connections makes everything work as it should.

spinks99 · 05-27-2010, 11:06 PM

I agree with IOWA-It seems like your circuit is not completing itself. As it is an aggregate problem, grounding could definitely be the problem.

Danny-Let me know what you find.

jgreen · 06-01-2010, 09:46 PM

I had the same problem with my Z240 this weekend. When I drop the trim tabs, the engine would almost stall and the computer readout would loose it's mind. My transom looks like it was wired by monkeys! I think you guys are right, bad ground is probably the reason. Looks like a day of crawling around is in order.