Temp guage false readings..

Since my cherokee only has the idiot lights I installed an electric temp gauge. The problem is I get false readings no matter how it is hooked up.

I have the sending unit placed in the back of the head where the factory one was installed (90 xj). I have tried my grounds in three different spots, 2 under the dash and now I have it grounded to the engine block ground on the back of the firewall. The power is plugged in to the ACC spot on the fuse box, but I have tried every single open spot in the fuse box and I always have the same issue.

The issue: When driving with no accessories on (excluding the radio) I get a false reading. IE.. driving down the road and use my turn signal, the temp gauge goes up, use my headlights, it goes up, etc..

While driving at night with my lights and heat or wipers on, it will typically show I'm running at 240ish.. when I turn it all off it drops to 210.

Anyone know what could possibly be causing this?

Have you tried wiring it (power lead) directly to the battery?

No I have not. It is a B&M black out gauge which needs to turn on and off with the ignition. I guess I could throw a toggle switch in if worse came to worse.

How about a little more information on the gauge and its sending unit--a link?

Is the sending unit a two wire affair or single wire?

What year are you working on? How is the unibody ground--the braided strap at the back of the head to the firewall? Do you have a later model with the fenderwell ground from the negative battery terminal?

Try running it through a relay. You could be getting inconsistent power. A relay will remedy this. I could easily be wrong but it sure wont hurt anything to try it. Just use an ign wire as your trigger.

I would just swap out a dash with a full cluster. Cheap and easy.

Johnnie Walker said:

I would just swap out a dash with a full cluster. Cheap and easy.

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I agree with Johnnie Walker. That is by far the very best option.

If you want to use an after market guage, you will need a good source of power 12 volts+ and ground. Use a volt meter to find a +12 volt source. It should be on anytime the ignition is on. It is important that it stays on even when the engine is turning over with the starter. The supply to the accessory will go off when the starter is applied. Things like the radio, blinkers etc's are on the accessory supply.

Is the sending unit the correct one for the guage ie; the resistance of both the sender and the guage matched? Is it a single wire or two wire sender?

Finally, both the sender and the guage need a good clean ground. Try to get a ground to the guage directly from the body. Clean all rust and paint fron the area under the wire (connector). You should try to avoid using pipe thread tape on the sender or any type of sealer that may also be an insulater. Pipe threads are tapered thread. They usually seal themselves when screwed in tight.

Honestly, I see no reason why it do not work properly. Many of us have after market guages in our XJ's and have no problem with them. I have an oil temperature sender in the AW4 and it work perfect.

It's a B&M Blackout Water Temp Guage part # 80331. It is a single wire from the sending unit and came with the sending unit that I'm using. It's been discontinued (picked it up for a good deal because of this). I called B&M and was basically told too bad so sad as they don't offer support for it anymore.