I have a 1991 Honda Civic Si that I put a JDM d15B Vtec in. I haven't had the temperature gauge working ever since, maybe before. I think my Cluster might be messed up, but I am not 100% sure how to tell. I bought an aftermarket temperature gauge and tried to install it in the temperature sending unit spot, and I tried to rig it up on the thermostat housing (where the cooling fan switch use to be) neither worked, because the adapters I was given didn't fit. I am coming here to see if anyone has any ideas on what I could do, or where to start to try and fix my problem. I really need to monitor my temperatures, and don't feel like "drilling and tapping" anything.

 

I assume when we say temp gauge we are talking coolant and not oil? If it's coolant, just use an adapter on the upper radiator hose and then run the sensor to that. That is where most would run the temp regardless.

 

sounds to me like you want to know how to wire up your temp guage?
or find out why your stock one isnt working?
well to start that wiring isnt at the thormostat thats just for the radiator fans
the signal wire your looking for is under your distributor bolted on the head
theres two sensors there your gonna want the one with the ONE WIRE if i remember right

should be a yellow/green wire
take your light tester to it at the head and see if it goes to the #3 wire on your cluster wiring

on your cluster theres two plugs one with 8 wires and one with 12
the temp guage wire should be on the 12 wire plug
wire #3 yellow/green

my guess is that your wires is broken ^_-
or that sensor that bolts to the head is broken

goodluck
let me know how it goes