False readings on after market temp gauge..
 

Since my xj only had the idiot lights I installed a B&M water temp gauage. I'm getting false readings when I turn on my headlights, heat, etc.. When my engine is warm and running at 210 turning on my lights and heat will cause my temp readings to go up as high as 240. When I turn it off it goes back down. Normally I'd just deal but I'm battling the cooling system so I need to ensure I don't overheat once it starts getting hot again.

Supposedly this is a ground issue but I have tried 3 different ground points (including the engine ground strap on the firewall).

Has anyone ran into this??

where are you getting your power for the temp gauge from?
fuse block? battery?
it the fuse block is it from an empty terminal?

Fuse block.. it's spliced in with the radio so it will turn on and off with the ignition.

You should get the power from a OPEN circut, you seem to be getting feedback from other components.

i agree. i would flat terminal on the end and just plug it into an open spot on the fuse block, whether it be batt or acc. you will not get any feed back as it has its own dedicated battery supply.

Ok, I'll see if I can find an open accessory circuit. I need it to turn off with my ignition.

Tried every empty spot in my fuse block. They all did the same thing.

well keep it plugged into the fuse block, you now have another wiring issue, however that is where is is suppose to be.... see if you can make the ground as short as possible. I am however at a loss because i have my CB, PA, Roof Lights, Gauges and Reverse lights wired off of the same body ground and they all have power either from the fuse block (cb, pa gauges) or the battery(lights) and hae no issues of interference or ALT whine. where is your gauge mounted? is it easy to remove it to test it?

It's mounted where the factory clocks were at in older models. The only thing I can think of is maybe the coupler for the ground is loose. I'll take it apart this weekend.

I called B&M and they said it's discontinued and have absolutely no info on it. Told me it was probably the sending unit thats bad. But I don't see how the sending unit would be affected by the headlights being on..

here is an idea! okay so on mine i have the 3 main wires (power, negative, and signal) and then the light bulb/socket has a separate 2 wires(power and negative) did you slice your light power into the main power for the gauge? or the light negative into the main negative? the way i run mine is that i have 2 main powers running to all 3 gauges, 1 for the guages and 1 for the lights, and then i have 2 negatives, again one for the gauges and one for the lights, then they one wire for the temp signal wire (the other one is mechanical oil pressure and the other is a volts meter). so in all i have 5 wires running all 3 gauges. and then the Tach is running off of its own everything. the main power is off an acc empty spot on the fuse block, the light power is off of the dash light fuse in the fuse block


sorry for the crude picture but this is my set up.

Mine has 3 wires.. power, ground and sending unit lead. I have the ground currently going to the engine block ground, was at a bolt next to the bracket for the gas pedal. The main power is currently on the ACC fuse spot and the sending unit lead is going to the sending unit (yea I felt dumb typing that).

hmmm well, i am not sure. that is really weird..... best i could think of now is that your sending unit did go bad lol...

but other than that.:wallbash:

you could replace the gauge..... mine are all the $15-$20 cheapo gauges. they seem to work perfectly too.