I just purchased a new VDO exaust temperature gauge for my '74 C-3. I already had some kind of a sending unit on my exaust manifold from a pre-existing exaust temp gauge made by another company. I disconnected the old wires going from the sending unit to the gauge, and connected the new wires to the old sending unit (which I don't know if it was good or not, by the way). The VDO set up has two separate wires going from the gauge to the sending unit joined at the end to a large loop-type terminal connection. I cut off the large terminal connector at the end, and just crimped the new wires into my old sending unit at the same place I disconnected the two old wires. The old sending unit is just a prod type that slips into the exaust manifold and has a nut on it to tighten it, with a crimp type fitting on the outside to connect the gauge wires to. I am no getting any movement at all on my gauge. Not the slightest needle flutter, and I have driven the car for an hour or so. I think I have all the wires hooked up to the back of the guage correctly (The light works and I have the positive and negative leads hooked up to the indicated terminals on the gauge. I used the same ground that is going to the gauge light). Is my old sending unit bad? Is my new VDO not compatible with my old sending unit? Did I make a mistake by cutting off the terminal on the new wires provided by VDO and just crimping them into the old sending unit? What else?
If someone out there has some experience or expertise on this kind of problem I would sure appreciate hearing from you. I would like to eliminate anything I might have done wrong before I replace the old sending unit, or send the gauge back. Thanks in advance!

'74 Turbocharged 350, "Molested to Perfection", class of '71

 

Update

 

I would not count on your old sender [thermocouple] being compatable with your new unit . Exhaust pyrometers will read instantly when you fire up your engine,and a good one is very responsive to temp. changes as you drive . Why did you just replace the gauge ???????

Geo

 

I agree... :yesnod:

 

......Thanks for your responses and help,guys. "Why did I just replace the gauge?" Mainly because I couldn't see how much of anything could be wrong with the sending unit. It appears to just be a metal prong inserted into the exaust manifold with a connection on the end to wire the gauge to. Also, VDO does not include a sending unit with their exaust gauges, so therefore I was hoping that the gauge was compatible with any sending unit. I was also concerned that any other type of sending unit might not fit the same configuration already in my exaust manifold. Thanks again for your suggestions. Looks like I might have to call VDO for some additional tech assistance. Regards,


'74 Turbocharged 350, "Molested to Perfection" , class of '71