1988 xjs battery condition indicator ?

[henheads]

i hope somebody know the answer and can help. batterys fine, charging, alternator ok. the indicator on my instrument panel
always looks 1/2 dead ie: 8-9 volts and incorrect, since i assume its not guessing and actual guage seems ok, is there a sender/transmiter for this, perhaps in the back not showing on the schematics. something simple and easily overlooked? call me touchy but with all the work in it, i like my guages
somewhat accurate

 

[Exotexs]

could be something as simple as the main wiring connectors behind the gauges panel needing removal and refitting, contacts do get corroded and "lazy" to transmit. If you were to remove the dash gauges panel, disconnect the large wiring connectors on the rear of the dash gauges panel, and use the eraser from a pencil to carefully clean any corrosion from the surface of the male contacts. you could also apply a thin layer of dielectric grease over the contacts too.

Ex

 

[maynard]

The grounding of the panel is poorlyd designed. Try running an new ground from the panel to the bady.

 

[LarryK]

Take a voltmeter and check voltage at battery. Then check voltage at battery gauge. There is nothing else to send to gauge. 1 thought would be to watch all gauges and see if the is a little diviation in their accuracy. If they seem to diviate from what they should replace the dash rectifier.

 

[henheads]

all other guages are good, voltage good, i noticed some varios colored wires off the battery terminal with i think a resistorbut corroted, one orange and forgot the other. could they have anything to do with it. or does the panel simply monitor the voltage directly?

 

[LarryK]

Any corrosion can affect voltage to the car. Clean and repair and check again. Voltmeter is wired in dash and tells you voltage of battery. You can check votage under dash and see if it is as guage.

 

[henheads]

im glad to find someone who knows his stuff, does the voltmeter have a seperate feed line to the battery or is it being monitored another way. my panel has a
multiple entry connection in the back. if guage can be verified from underneath
that would be great, can you be more specific as to where to test voltage underneath or do i have to pull the panel out. corrosion was a bad choice of words, weathered more appropiate and thats solely the housing, contacts were clean. voltage reading at battery and alternator were good. and other guages are reasonably accurate for their design

 

[LarryK]

Can't say I know all my stuff, been about 20 yrs. since I worked on the XJ 3.6 or the XJ40. I would check at the cigar lighter. You can ground one terminal of a voltmeter and probe the center of the socket and get a reading. I would look under dash and find a Red wire and hook the positive of the voltmeter to it and ground the black voltmeter line. This should give you voltage to dash. Also, what were the readings at the battery ( engine off and engine running )? Should be 12.75+ with engine off and 14.+ while running. You can also remove instrument cluster and once off, you can seperate the back and check the gauge grounding within the unit. Just be careful with the cluster being old and plastic.

 

[Michael J.]

Look at one other thing. There is a braided ground strap that connects usually from an oil pan bolt at one end and the other end connects to the front suspension sub-frame. Check for a loose bolt or corrosion at either lug.

This strap connects the engine ground to the body. The higher the current draw, the more resistance and lower the voltage when corroded or loose, but when under low current draw, voltage will seem normal.