Ohm readings to ground vary for gauges HELP

[shovelluv]

This is regarding my oil and temp gauge.... I have a very well grounded engine to chassis. It is grounded heavy to the firewall, battery, core support and fender. Heres my problem with the engine running, yes, the sender is for a gauge part s330. If I take my meter, one lead to the sender the other to chassis ground i get a closed circuit to ground which pegs my gauge. NOW, If i put my ground lead on my meter to the negative on the battery cable on the block it reads 10ohms, if i put my meter ground lead on the oil sending can direct I get 22ohms which is what I want and would put my needle on my gauge at about 1/2 way. I have the same problem with my temp sending circuit. I have not re-installed my gauge cluster yet because I just restored them, i am testing to see what the ohms are going to be with it running at normal temp.

 

[65-440]

Just to make sure you understand, the temp sending unit varies resistance to ground according to temp. If you're getting full ground at the sending unit terminal end then the sending unit is bad ..... and you should not have 10ohms. Resistance between any grounds on the vehicle, that is way too much !

 

[shovelluv]

Yes, you are correct, oil and temp they vary to ground with psi /water temp change. If i turn OFF the engine at the ignition switch and check the temp ohms, when it is at 180 degrees it reads 29 ohms to ground GOOD, as soon as i turn it to ignition it goes to ground. it is only when the ignition is on that it reads to a closed circuit to ground. Temp sender is new and good, i tested it as did with the oil sender. Its like everything is reading about 30 ohm low thru the chassis with the ignition on. Get this, I have no issues with my fuel gauge with ignition in the ON position, just temp and oil. Thanks

 

[shovelluv]

The oil sender reads 23 ohms on my meter from the oil sending end tip to engine ground, thru the ohm meter, while running. If i move it to chassis ground i read a closed circuit to ground.

 

[oldbee]

I think you’re saying per the readings that there is a bad ground somewhere. Try this, if you have batt. jumper cables; hook the red&blk to net.post on battery. & other ends, one to block & one to firewall. See if the readings stay the same. Easy/cheap diagnostics first.

 

[shovelluv]

I do have plenty of ground from engine to chassis. I did notice if i disconnect my alternator field wires and start it, I do not go to ground on my gauges. The blue wire on alternator field connector had 2 wires on it, one of the actually went to the positive side of the coil?? and the other to the regulator so im looking into that because i cant find one wiring diagram with a dual resistor that has field wires going to the coil.

 

[shovelluv]

Well, turns out it was something in the alternator causing some kind of high resistance to ground with ignition on. Which, in turn caused my gauges ohm resistance to act goofy.