Dash lights and gauges question

[Sonny]

I've been trying to solve an electrical problem for about 2 weeks now on my 1970 318 Belevedere. None of the dash lights work, and there is no power on either side of the fuse. I can add 12v to the fuse with my power probe and get the lights to come on nice and bright. Question is, why doesn't that make the gauges (fuel, oil, and temp) work also? I replaced all the engine side harnesses and the rear tail light harness. Is there a vr or a capacitor or something that would cause the gauges to not work at all? Thanks for any suggestions.

 

[moparjohnny]

I've been trying to solve an electrical problem for about 2 weeks now on my 1970 318 Belevedere. None of the dash lights work, and there is no power on either side of the fuse. I can add 12v to the fuse with my power probe and get the lights to come on nice and bright. Question is, why doesn't that make the gauges (fuel, oil, and temp) work also? I replaced all the engine side harnesses and the rear tail light harness. Is there a vr or a capacitor or something that would cause the gauges to not work at all? Thanks for any suggestions.

you have a light dimmer switch on lower dash for headlights,park lights. it also controls fuel and oil and temp lights that one switch control all of those, switch might be bad and need a rebuild, i had same problem last year,might want to start there.

 

[J. Cower]

Yeah. Just did this on my 71 SSP. The power runs through the dimmer switch before getting to the fuse for INST PANEL lights on mine so nothing will show power there if that's bad.

 

[khryslerkid]

Yeah. Just did this on my 71 SSP. The power runs through the dimmer switch before getting to the fuse for INST PANEL lights on mine so nothing will show power there if that's bad.

Or not turned up to bright.

 

[Shorthorse]

Lets see if I've got this right.
Power to the dimmer switch is fed from the light switch via the Black wire when the lights are turned "on". In the dimmer switch, that power feeds through the rheostat mechanism and out on the tan wire to one side of the fuse. Since that same Black post feeds exterior lights and they work, the light switch should be good. So, the black wire to the dimmer switch (input) or the dimmer rheostat mechanism, or the tan wire/connection from the dimmer to the fuse is where the problem lies. Given the history of the dimmer switches, that's probably where you issue is. The dimmer rheostat mechanism can be easily checked with a meter before plunking down the money for a new one.
From the other side of the fuse, the orange wire feeds the dash lights on the connector pin #1. The orange wire feeds other lights such as the gear selector, radio, tach and clock, so if there is no power at the fuse, they should not be working also.
http://www.mymopar.com/downloads/1970/70BelvedereGTXSatelliteRoad RunnerA.JPG
http://www.mymopar.com/downloads/1970/70BelvedereGTXSatelliteRoad RunnerB.JPG

 

[Sonny]

Short horse: thanks for that comprehensive analysis! I took off the dimmer switch and it's full of blue/green corrosion. I tried to clean it but no luck. I'll confirm I have voltage on the black wire, and out to the tan wire tonight. But you're right my exterior lights work good. Where's the best place to buy the dimmer?

 

[Shorthorse]

View attachment 389482 Short horse: thanks for that comprehensive analysis! I took off the dimmer switch and it's full of blue/green corrosion. I tried to clean it but no luck. I'll confirm I have voltage on the black wire, and out to the tan wire tonight. But you're right my exterior lights work good. Where's the best place to buy the dimmer?

Great, looks like you got it. A quick look online showed me those switches aren't cheap. I'm sure someone here will know the best deal for a quality switch. Here's an old time remedy (shown to me by a friend) that I've used on severely corroded battery terminals. Pour some Coca-Cola on the corroded part. The acid in the Coke will make the green disappear. Of course, if the connection between the spring and the contact have too much gap, the arching will cause the corrosion to form again.

 

[Billccm]

DeOxIt might save it. I've been amazed at how that product works.

 

[R/T]

Clean the dimmer, even expensive nos ones have been known to not work right out of the box. I took mine apart and cleaned the contacts!

 

[bschomske]

Would this switch keep the dash lights on all the time? My problem is with my dash lights staying on all the time..My switch does not brighten the dash lights either.But it will turn on the dome light.Also my gas gauge doesn't work.Someone stated that this switch also takes care of fuel and oil...I didn't know that..Maybe i should change mine?

 

[R/T]

Guage light not the fuel level.

 

[Shorthorse]

Would this switch keep the dash lights on all the time? My problem is with my dash lights staying on all the time..My switch does not brighten the dash lights either.But it will turn on the dome light.Also my gas gauge doesn't work.Someone stated that this switch also takes care of fuel and oil...I didn't know that..Maybe i should change mine?

Your issues are different from Sonny's. His was basically an open circuit while yours sounds more like a short.
First, you want to start a new post and provide all the information you can, year,make, model. Include any info on the testing you have done so far and any info about any wiring modifications that might exist. Check your entire lighting system first so you can give detailed information about the symptoms. The light and dimmer switch are not related to operation of the fuel & oil gauge. Their only relationship is that their wires eventually converge into the same wiring harness and connector.
You'll get help. This is a great site.

 

[bschomske]

thanks Shorthorse..I guess the only thing i can add is that the car just finished a total restoration on a 1969 roadrunner hard top.When the car was put back together the same harness went back in..The only real change was the gauge package was changed to a better looking gauge package without a crack in lens.So when the car was done this is a problem that came up that needs fixing...I don't do much electric but would like to get some direction to take......But thanks again for your attention to this pain in the *** problem...

 

[Shorthorse]

thanks Shorthorse..I guess the only thing i can add is that the car just finished a total restoration on a 1969 roadrunner hard top.When the car was put back together the same harness went back in..The only real change was the gauge package was changed to a better looking gauge package without a crack in lens.So when the car was done this is a problem that came up that needs fixing...I don't do much electric but would like to get some direction to take......But thanks again for your attention to this pain in the *** problem...

That's good information. Now seriously, start your own new post. Post it in the Electrical & Ignition section. You will get help. I guarantee it. The best advise I can give you up front is make sure you have a test light.