1967 Firebird. I need some help and advice to make sure my temp light is working properly. When I turn the key to the on position, the oil and gen light both come on. The temp light does not. I grounded the green wire to batt ground and the light comes on with the key in the on position. It does not seem that the car is overheating but I would like to make sure the sensor is working. First, should the temp light come on when I have the key in the on position like the oil and gen light. Second, I did put in a new temp sensor when we rebuilt the engine. However, I would like to test the sensor to make sure it is working since the light does not come on when I have the key on and the only time it should come on when the car is running is if the engine overheats. I know I should probably look at replacing the oil and temp lights with gauges but I am trying to keep the car original since it is pretty much unmolested other than the engine that we rebuilt.

In addition, when the car is running the dash and gage lights, interior lights, headlights, taillights all flicker a bit. I did put a new alternator on the car when I rebuilt it. I bought the alternator from alternatorparts.com. It is a rebuilt 10NDN case but is upgraded to a 140 A rating with 50 A stators. I have also checked all of the ground straps on the engine, frame, body, grounding under the dash, and have a good ground from the battory right to the fender just like the factory. My Ohm meter shows good continuity in all locations when I run a wire from Batt ground to unpainted and unrusted surfaces on the dash, firewall, engine, frame, body, ect.

Any suggestions you have on these issues would be much appreciated. Thanks

Ron

By the way, I should have mentioned that I can reproduce the flicker of the interior lights on the dash, dome light ect when the car is not running. If I turn the interior lights on (full left on the light switch) with the key in the off position, open the door, and push in on the door light switch all the interior lights are a bit more dim. When I release the door switch, the lights get brighter. I checked all the wires, connections, and grounds the switches on both doors and they seem to test okay.

You tested the temp sending unit correctly.
And no, it does not come ON with the key ON. Only the GEN and OIL lamps should come ON with the key ON.

As far as the flicker goes, disconnect the alternator and then start the car up. If the flickering stops, you've found the issue.

The door switch issue, sounds about normal to me - Wouldn't be too concerned with it.

Thank you Dr. Been out of town for a few days and wasn't able to respond to you. I appreciate the help. I will try the alternator tip to see if there is an issue there.

Hi again. I have been out of the country for a few months but back home now ready to do some work on the bird. I did the test that Dr suggested a few months ago was no change in the operation of the lights with the alternator disconnected. I am continuing to try to run down intermittent electrical issues on my 1967 Firebird. Trying to find all the grounding issues that come with buying a 50 + year old car that sat since 1978 until March of 2020 has been a fun (but sometime frustrating) process. I have all the engine and chassis grounding straps in good shape and they test fine with a test light and a meter. I am working on the grounding under the dash. I have the grounding wire mechanism that attaches to the Bright Light indicator, the dash, and the gauge cluster in place. That ground test fine too with test light and meter. I continue to have issues with intermittent dimming of the dash lights, headlights, interior lights ect when the car is running. I do not get the dimming/flickering when the car is not running but the lights are not as bright when the car is not running. I am not as concerned about that as I am about the dimming and flickering when the car is running. I have a couple of questions. 1. The alternator is a AC Delco Remy 10DN. I was checking those connections this morning and noticed that there is not a ground wire on the ground terminal of the alternator. I am sure there was not a wire there when I took the old alternator off because I take pictures of everything before I disassemble something. Can you tell me specifically where that ground wire goes on the car from that terminal. I wasn't able to find any pictures or info on the web and my electric diagrams just show a ground symbol but not the location. I am not sure if it grounds to the alternator case, the chassis, the voltage regulator, or somewhere else. If you have a picture of the wire and where it connects that would be great. By the way, I connected my test light to Battery + and then grounded it to the every area I could try on the alternator including the ground terminal that does not have a wire connected, the alternator case, the alternator bracket and have a good ground in all of those. 2. I know that there is a grounding mechanism that attaches to the bright light indicator, the gauge cluster, and the dash that is important for proper dash lighting. That is the only ground I can find under the dash. I do not see a ground near the light switch, the radio, the heater controls or anywhere else. Are there other gounding straps under the dash that I am missing that might be causing my issues. If there is any kind of under the dash grounding diagrams that would be very helpful. I really appreciate the input and solid info I receive from the people on this site and hope you can help. Thanks Ron

Update on the flickering and dimming issue. I used my meter to test the voltage in the charging system under as much load as I could get.
Turned on the interior and exterior lights, the heater on full blast, the radio, put the car in reverse so backup lights were on, opened the doors, and even opened the glove box so the charging system would be under as much load as possible. My battery tested at about 12.5 volts before I started. The alternator was also throwing at the about the same voltage. When I put the car under electrical load and had someone give me a few more RPMs than idle, the volts the volts did not change. So, I started looking at the new voltage regulator that I installed a few months ago. I noticed that there were only a few strands of wire left on the case ground wire and the insulation had worn off because it was rubbing on the corner of the VR case. Probably been that way for decades since it appears to be the original ground wire and the way it goes around the VR case is not the best design since it is prone to rubbing off. After I repaired the ground wire and made sure we had good ground at the VR, I am now getting almost 15 volts under load on my meter. Best of all, no more flickering or dimming lights. Just goes to show that you really have to look closely at a lot of things and the smallest and least expensive fix can make a huge difference. Thanks to all of you for your suggestions and help. I am sure I will be back with another request soon. Keep up the great work.

Thats awesome!