[injected1]

Ok, I have a 1995 Mariah Z202 Shabah and am having some issues with my gauges. Sometimes they will work fine, but most of the time they will sweep over and read their maximum as if they were getting too much voltage. I assume they work by reading variable voltage sent to them from a sending unit, but I can't figure out why ALL of them do this at once. I'm starting to suspect it to be a ground wire touching a hot wire somewhere and backfeeding them. I think this because there's also 3 of my rocker switches light that light up faintly when this occurs and sometimes if I blip the throttle it will correct and as soon as the lights go off the gauges are working. I'm assuming the throttle jars something apart.However, if they are working, they just randomly go back to doing the same old thing again. Does anyone have any ideas? I'm on lunch break from work right now and am going to get back after it with a multimeter after I get off.

[recelect]

Originally Posted by injected1

Ok, I have a 1995 Mariah Z202 Shabah and am having some issues with my gauges. Sometimes they will work fine, but most of the time they will sweep over and read their maximum as if they were getting too much voltage. I assume they work by reading variable voltage sent to them from a sending unit, but I can't figure out why ALL of them do this at once. I'm starting to suspect it to be a ground wire touching a hot wire somewhere and backfeeding them. I think this because there's also 3 of my rocker switches light that light up faintly when this occurs and sometimes if I blip the throttle it will correct and as soon as the lights go off the gauges are working. I'm assuming the throttle jars something apart.However, if they are working, they just randomly go back to doing the same old thing again. Does anyone have any ideas? I'm on lunch break from work right now and am going to get back after it with a multimeter after I get off.

I would bet you have a ground issue. Not neccessarily a ground touching power, but a ground not making good contact. It would cause both your issues... Find the grounding block under the dash and make sure everything is clean, tight, and corrosion free. If it is, Find the source of the grounding blocks ground. Make sure that is clean, tight and corrosion free. My bet is you will find something loose, dirty or corroded...

[injected1]

Thanks. I will do that first thing tomorrow.

After working on it for about 3 hours this afternoon I have more information. The very strange thing is that the main power distribution block under the dash shows a normal 12.5 volts with the key off. When I turn the key to the "on" position, it drops to about 7.5v. I haven't got a chance to check it while the gauges were working correctly for comparison, because they only worked for a bit when I first started it this afternoon and haven't worked since. It shows 7.5 volts with the key in "on" position with the engine running or off. I checked everything back at the battery and it's getting 13.5+ volts while running from the alternator, so everything is good there.

Is it normal for the gauges to peg when the key is turned on before starting? I never noticed before.

[injected1]

Ok, taking a break to find a 5/16th" wrench and cool off. lol I have determined that this problem is isolated to the gauges and when it occurs it drops the voltage to everything else in the front of the boat. I unplugged the harness that only feeds the gauges and all other voltages are normal. I cut the power and isolated it from the rest of the boat. I then hooked a hot wire to the hot and poof. They were wacky just like normal, however the voltages were normal everywhere else. I went through and clipped the sender wires one by one and am hooking them up one by one. However, I noticed with the sender clipped, the oil pressure gauge still pegs. I am looking for a wrench to unhook the common power to it to see if it is the problem. The common ground on all the gauges just runs the lights in the gauge, but I clipped it just to be safe. They still do the same thing without it. This has been such a pain. I've been all over this thing trying to fix this.. Phew!!

[recelect]

Originally Posted by injected1

Ok, taking a break to find a 5/16th" wrench and cool off. lol I have determined that this problem is isolated to the gauges and when it occurs it drops the voltage to everything else in the front of the boat. I unplugged the harness that only feeds the gauges and all other voltages are normal. I cut the power and isolated it from the rest of the boat. I then hooked a hot wire to the hot and poof. They were wacky just like normal, however the voltages were normal everywhere else. I went through and clipped the sender wires one by one and am hooking them up one by one. However, I noticed with the sender clipped, the oil pressure gauge still pegs. I am looking for a wrench to unhook the common power to it to see if it is the problem. The common ground on all the gauges just runs the lights in the gauge, but I clipped it just to be safe. They still do the same thing without it. This has been such a pain. I've been all over this thing trying to fix this.. Phew!!

I would still make sure you have a good ground.The common ground runs the lights yes, but also the gauge. You might be looking at the hot wire for the lights. The grounds should be white or black. Most likely white. You can get low voltage readings if the ground is bad, and this can cause the guages to spike. Try running a jumper from the ground of the battery to the grounding block under the dash and see if this fixes it. The only way you would drop that much in voltage is if you had a direct short that is unfused (which would cause a fire) had a large power draw from a motor (and the battery is weak, which it doesn't sound like) or if you have a bad ground.

Also the lights on the guages should not be on unless you have your navigation lights on. If they are, I am positve you have a ground issue, or if you have had to replace any guages, maybe they are hooked up backwards. The only other thing I would look at/try is to see if your trim sending guage is causing problems. The trim sending unit wires often corrode and short, which could cause some issues, but I still don't think that is what your problem is.

If you're in Colorado, you can always bring it to my shop. I specialize in these issues.

[injected1]

Originally Posted by recelect

I would still make sure you have a good ground.The common ground runs the lights yes, but also the gauge. You might be looking at the hot wire for the lights. The grounds should be white or black. Most likely white. You can get low voltage readings if the ground is bad, and this can cause the guages to spike. Try running a jumper from the ground of the battery to the grounding block under the dash and see if this fixes it. The only way you would drop that much in voltage is if you had a direct short that is unfused (which would cause a fire) had a large power draw from a motor (and the battery is weak, which it doesn't sound like) or if you have a bad ground.

Also the lights on the guages should not be on unless you have your navigation lights on. If they are, I am positve you have a ground issue, or if you have had to replace any guages, maybe they are hooked up backwards. The only other thing I would look at/try is to see if your trim sending guage is causing problems. The trim sending unit wires often corrode and short, which could cause some issues, but I still don't think that is what your problem is.

If you're in Colorado, you can always bring it to my shop. I specialize in these issues.

Well, through all the hooking, unhooking, cutting, and resplicing,I have managed to get the tach and temperature gauges working. I was unhooking the ground, which was verified through a multimeter. Unhooking it had no effect whatsoever and the gauge stayed pegged, so I assumed it was only for the backlight (similar to the switchs' lights). I took it out and ran it Sunday with all but the tach and temp unhooked (in case of fire) just to try out the new motor. Man, I wish all the gauges were working because with the new High Five prop and close to 400hp small block, the thing is a beast compared to the old 260 horse motor and aged aluminum 3 blade prop.