Temp. Gauge On 79' Gmc

[BAD2500HD]

My 79' GMC K25's temp. gauge isn't work it hasn't since i bought it about 2months ago anyhow what is the best way to find out if its the gauge or the sending unit ? and how do i check it out . Thanks !

[Workin8.5]

My 79' GMC K25's temp. gauge isn't work it hasn't since i bought it about 2months ago anyhow what is the best way to find out if its the gauge or the sending unit ? and how do i check it out . Thanks !

 

 

Take the lead off the sender and I think the gauge goes all the way hot.Groung that wire and watch the gauge. Gauge not responding? Bad gauge,bad ground to gauge,bad connection or bad wire.If it does respond then just replace the sender,they're not that expensive.