Inliners International Forums General Discussion Electrical Something strange happened....

Here's a wierd thing that's got me scratchin' my head and saying "Huh, what the hey...?". All through the project of getting my truck (69 Chevy)re-assembled, I had headlights working, but no tail lights. Then I found one day that the tail lights are now working."This is good.", I thought to myself.
Yesterday, I was out in the driveway tinkering around. I had forgotten to re-attach the instrument bezel to the dash.It's held on by 6 screws. After securing the dash bezel I pulled the headlight knob. Huh????? No headlights!!!!! GRRRRRRRR, I hate electrical problems!!!!!
Today, I start the truck,and while it is idling I pull the headlight knob,and VOILA,now the lights work.
Truck not running...they don't work.
Truck running.....they work! Oh well, guess I never have to worry about accidentally leaving them on during the day and running the battery low/dead.

GROUND...GROUND...GROUND. Check all the ground straps. Bed to frame, cab to frame (located just under the rocker panel),front clip to the frame(just ahead of the right front wheel) Motor to the frame,cab.There is a small ground strap from the inst. panel printed circuit to the dash. Sounds to me like you are acquiring your ground through the transmission/drive shaft/rear end/ springs/to the frame.I had a truck one time (auto) that the lights would only burn when it shifted to hi-gear.Good luck...SCRAP

Thanks for the tip. I never thought about a ground from intst. panel to printed circuit board....that could be it.

If this ground is bad it only effects the dash lights and gas gauge. When you turn the lights on the gas gauge will take a dive to empty and your blinker indicators will burn weakly. The head lights will work OK..Again make sure all your body units are grounded to the frame!!!SCRAP

Do the taillights also come on only when the engine is running? And does the engine have to be running for the headlights to work, or will they work when the ignition is on but the engine not running?

An intermitent problem is the most difficult to solve.

Make sure the connectors on the firewall are secure. Wiggle the plugs a little. Often on 60s (cars/trucks) these come loose.

Good luck.

Do you have your headlight power feed wired through the ignition switch?

John is right. Unplug this connector and clean it if you can. This plug is located near the master cyl. is held together with a screw that is famous for stripping so good luck. If your truck has been sitting outside with the hood off in the weather you can bet you have a issue at the plug...SCRAP

John and SCRAP,
Ok I will check that also.

BaldEagle, The tailights come on with engine off. It's only the headlights that are acting whacky.

Also check that dimmer switch on the floor. That thing is in a place it gets a lot of water off your feet, door seal leaks and that windshield that has a always leaked on all those trucks. SCRAP

The head lights and tail lights get their power from different circuits. It looks like your head lights are tied in to the ignition or a hot when the key is on pin or fuse on the fuse block. Check to see if someone hasn't tied the headlight wire on the fuse block to a different power source than the headlight fuse.

I went out and looked on my truck but upside down and backwards at 10:55 at night doesn't work too well at my age.
No headlight fuse.
According to the wiring diagram there is a 12 gage red wire that ties into the main power feed harness on the back side of the fuse block. Or close to it where several wires tie in together.

I can't recall for sure, but I think the 69 has 2 ground wires from the battery, one to the block and one to the inner fender. Check the ground to the inner fender -- this is the one that all the accessories use. Once upon a time in my then girlfirend's 72 Nova, this wire had corroded while still looking good on the outside. The headlights would glow dimly until you pressed in the clutch!?

regards,
Leon

A bad ground should make the headlights dim it should have no effect caused by turning on ign. Headlights are not fused they normally run a fusible link or an auto reset breaker. The floor dimmer on a chevy truck has 3 wires to it one is the power coming from the headlight switch the other 2 go to the seal beams one is high beam power the other is low beam power. the dimmer switch is not ground effected.
In 70 series chevy trucks I have run into many that do to resistance melted the plastic connector on the back of the switch causing all kind of weird things to happen. this is the first place that I would look. If your headlights are turning off and on with the ignition you either have a short or someone has miss wired your system.
The main reason to try to find the problem is if you are pulling power from another fused circuit you could be driving at night and with the addditional circuit load blow a fuse. Then no headlights. That could be fun on a dark country road in the rain. Your tombstone could read "I should have fixed my wiring".
Seriously you need to fix it. If your library has a copy of the GM service manual for your truck or if they subscribe to a system of computer manuals the should have information you need. with a flow chart for tracking down the problem. Also you mentioned you had thighten the bezel check if it moved things enough to cause your problem then adjust or repair fault then retighten.
Good Luck