Some of you might have been following my posts in the 1965-70 Forum regarding what I thought was a TCS problem in a 1970 Monte Carlo.

The major issue was that I could not make the temperature idiot light come on when I grounded the wire connected to the temperature sending unit. The problem was a very poor crimp between the wire and the terminal that attaches to the temperature sending unit.

I discovered this due to the issues we were having with the dashboard lighting in general. We had to replace the printed circuit board to get things working again. I tested all of the circuits before we re-installed the instrument panel and dash to confirm that everything worked as expected. After the dash was reinstalled the temperature light would even come on during the start cycle like it should.

I was tracing circuits based on wiring diagrams and the TCS information in the shop manual. I was finding lots of crazy things done by prior owners. The engine is a 350 from a 1975 Chevelle. The dual post (hot/cold) temperature sending unit that was in the left head had been replaced by a single terminal (overheat only) sending unit in the right head. The TCS solenoid had been removed as well as the idle solenoid. Those wires were just left hanging and had laid against the exhaust manifold in the right rear area. In general I was surprised that things worked as well as they did electrically.

I have been troubleshooting this on and off over the last week. The part that really confused me was that I was able to measure voltage at the wire connected to the temperature sensor. Yet when I grounded it the temperature light did not light.

I decided that there must be some other wires damaged/crossed and the voltage I was measuring was not coming from the circuit for the gauges. My plan was to connect a 12 volt test light to the wire and start pulling fuses to find the source of power.

The "aha" moment was when I connected the test light. It did not light! So even though I had measured voltage there was not enough current to power the light.

It only took me about 5 minutes to track the problem to the wiring that had been added to connect the temperature sensor wire originally on the left side of the engine to the new sensor on the right side. Whoever added that extension has tried to crimp a slide-on spade terminal to a 20 gauge solid wire. The crimp made just enough contact to give a voltage reading but not enough to pass any current.

This was a big reminder to me that electrical troubleshooting has to be organized and systematic. Keep focused on the simple stuff!

Last edited by Rusty 37 Master; 09/25/23 06:30 PM. Reason: Added info.


VCCA #44680