Temp Gauge issues

Jay_G

Ok, just looking to see if anyone else has had this issue before. I have a 46 pickup that I have been driving about 5 miles one way to work and back. It has been cold in the 50s and 60s. The temp gauge is running slightly below 1/2, where it normally does during the daylight. When I turn the lights on to go home after it has sat all day the temp gauge reads hot (almost pegged). I turn the lights off and back to normal. Also if I run the engine up with the lights on it the gauge will drop to normal, if I go to idle (lights on) back up it goes. Now the dash lighs also go dim (slightly). Headlights are fine as they are on a relay. This is sill 6 volts. My thought is a battery going bad or a ground issue at the dash (but the gauge needs no ground) or a lose commection with just enough resistance that the draw on the electrical system becomes an issue.

Thoughts? (other than to much information?) I still need to do a Volt meter test but everything starts so well and the headlights don't dim I don't think that is the problem.

Jay

Unknown

Sounds like you may have a short between the dash lites and the temp guage, I'd check out the wiring behind the dash to make sure. Yeah, I know it's a pain in the a--! Also might be the wire going out to the sending unit on the cyl. head getting a ground, maybe thru one of the dash lites. It would be a low resistance ground thru the filament of one of the bulbs. Good luck.

[Deleted User]

Make sure you are positive ground. Walt.

Jay_G

Up date on the Gauge. It rained last night and the truck sat out uncovered so this morning it was a little damp inside. The temp never went below 3/4 on the hot side. So I would say a wet cloth wire harness may be part of the problem now. Which points to an overall wiring issue. Guess it is time to put the new one in.....

Jay

Park_W

You may be losing voltage through the ignition switch contacts or in the power feed wire from starter solenoid to ignition switch. These gauge systems are made to be pretty tolerant of voltage variations (within reasonable limits), so there must be something going on. Note that with the gauges in a '46, the temp gauge "rests" on the hot side of the gauge. That means it takes power to drive it down to where it should be. So the behavior suggests it may be getting unsufficient voltage when you're idling or when the lights are on. It would be helpful to measure the voltage at the gauge's feed wire (from the ignition switch) and see what it reads in both circumstances ... engine revved up vs. idling, and with engine revved a bit, what effect turning on the lights has. Also, with ignition on, check the voltage going in and coming out of the switch. Shouldn't be a difference, or maybe 0.1 volt or so.