Assembled dash back into my 69 rag top and when I switch from low beams to high beams all headlights flicker and dim.Any ideas??? I have changed out the dimmer switch and the headlight switch.Please Help.
Grounds would be my first guess. Do you have clean dedicated shiny bare metal ground wires and cables and mounting points connections everywhere they need to be? For example between headlight switch and dash? (you say you replaced your dash...freshly painted? Headlight switch needs to be mounted securely to BARE metal...not painted metal). Same bare metal between bright light switch and floor? Same paint scraping routine at the bolted connections between dash and body? If you did not...did you add a clean dedicated ground wire somewhere between dash and body with paint scraped off? Proper straps/cables between body and subframe? Subframe and engine? Subframe and Radiator Support panel? Battery and engine? Was your dash removal part of a vehicle restoration? Common mistake: If any of the dash or parts of this car were fully repainted, did you take the time to COMPLETELY remove/destroy your beautiful new paint job down to shiny bare metal at EVERY electrical connection, ground, and switch mounting point? This is critical. Nothing kills electrical systems like an over-restoration including fresh paint on everything...you gotta grind and sand that pretty new paint clean off the car at key locations before reinstalling some components...
2nd guess would be a bad hot wire connections or even a bad switch (do not assume your replacement switches are good...might be smart to test them with an ohm meter and make sure they provide zero ohms when contacts are closed.)
Is it doing this when car is running only? Or also when car is shut off and you're testing lights only with the battery. If while running only:
3rd guess would be voltage regulator. When your lights are dimming and flickering, what is voltage doing at the battery on a meter? If it's fluctuating or dropping here while vehicle runs, likely you have a voltage regulator problem.
4th guess would be alternator. Test alternator for proper operation.
Wow, great information.Car is not running when this happens.I belive I attached all grounds.Did not know there was a cable between the sub frame and the body.I can see the volts drop to around 4 to 5 volts when I switch to high beams.Thank you very much for all that great info.This site has the best group of people.
Just for clarification...I'm not an originality guy...honestly not sure how many ground straps and cables were there originally or where they should be.
But if you're willing to toss originality aside, one of the best things anyone can do for any vintage vehicle electrical system is to securely ground EVERYTHING. Otherwise if you think about the path the electricity needs to take from your headlights and switches back to the battery...through rubber subframe mounts? Rubber padded engine mounts? Rubber radiator support mounts? I'm a firm believer in chaining ALL of these items together with quality ground straps, whether Pontiac put them there originally or not. Usually they can be mostly hidden. Often that alone brightens everything up and eliminates a whole lotta gremlins...
I'm also not promising you this is your actual problem. It might be something else. But this is where I'd start if it were me, because it's a valuable improvement to the car whether it fixes the immediate problem or not. But often if a high electrical load causes a large voltage drop as you describe, that can also be an indication of an overloaded/high resistance connection or wire somewhere on the hot side (dirty/rusted/corroded fuse or plug or nearly-broken or drastically undersized wire, or partially burned fusible link maybe?). These connections will carry electricity up to a point...but when asked to carry MORE electricity that the weak link can handle, the resistance in that location gets too great, heat builds, heat causes resistance to increase yet more, lights flicker...etc. Just like it would if trying to push all that current thru the only available ground, which if lacking a proper strap might be a rusted clip attached to a rusted brake line attached to a rusted subframe...
You can temporarily trouble-shoot a ground problem with a long jumper wire too (not too thin...think maybe 12-ish gauge wire). Attach one end securely to negative at the battery, now with the lights on touch the other end firmly to clean metal on various places...dash/floor/subframe/engine, wherever...if suddenly your lights brighten up when you touch that wire to one of these locations...you've absolutely confirmed your problem is a lack of an appropriate ground path.
