fuel and temperature gage not working

[jtdeweber]

Howdy all,

I have read the other two posts regarding my problems and have at least some idea of where to begin. My temperature and fuel gages are not reading, and here is what I have done so far with more explanation for each.

Fuel gage - I pulled a gas tank out of a late 70's model Blazer and am using it's sending unit. However, it is not reading properly. If I remove the sending unit wire that goes to the fuel gage and ground it, the gage pegs. If I take the sending unit out of the tank and move the float up, the gage shows empty ... at half way up - it shows one quarter of a tank ... and at empty it shows full.

Temperature gage - original equipment here of course. With the key on, the wire light blinks on and off at the sending unit, and inside the truck at the gage. However, the gage does not move at all.

I do not have a volt/ohm meter but am sure I can borrow one if that is the route that I need to take.

[jtdeweber]

Did another check. The temperature gage also pegs when connected to ground. I am going to buy a temperature sending unit today and see if that solves the problem.

[jtdeweber]

The temperature gage now works! I guess I should have checked it before I posted about it.

Any thoughts on why the fuel gage works backwards?

[nfury8]

Any idea if the Blazer fuel sender is supposed to be electrically compatible with the Dodge?
You will need an ohm meter to verify this.

[jtdeweber]

It probably is not compatible. I don't have an ohm meter but I think since it is working, though backwards, I will just use it as is and keep track of miles. I get the feeling that the sending unit sends a signal the reverse of the original dodge sending unit.

[EGroscup]

Gm used a backwards sending unit for years. 0 to 90 ohms. 0 at the bottom for empty and 90 at the top for full. I don't know offhand what our gauges are calibrated to, but I do know that they increase resistance as the fuel level drops.

[jtdeweber]

Thanks for the great reply. I thought that it probably had a reverse system. I know very little about electrical stuff but am learning slowly.
Is using the guage as is likely to damage anything?

[surfnuke9]

our fuel guages read empty at about 70 Ohms and Full at about 7 Ohms.

Ford used a tank sender in the early 70's that is REAL close to ours. it runs between 8 and 80 Ohms with 80 being empty. They changed to the higher resistance senders about 1978 or so.