Hi everyone, I'm new to this forum. I'm having an electrical problem which I've never been good with.  My lights are dimming in time with the idle. When I disconnect the battery ground, the problem stops. The alternator and voltage regulator are fairly new. When I originally noticed the problem, the starter solenoid began smoking. After I cleaned the battery terminals the smoking stopped, but the lights still dim and the ammeter still bounces. Does this sound like a bad ground?  

dangerdan:
Hi everyone, I'm new to this forum. I'm having an electrical problem which I've never been good with.  My lights are dimming in time with the idle. When I disconnect the battery ground, the problem stops. The alternator and voltage regulator are fairly new. When I originally noticed the problem, the starter solenoid began smoking. After I cleaned the battery terminals the smoking stopped, but the lights still dim and the ammeter still bounces. Does this sound like a bad ground?

Welcome to the Forum.  I'm not sure why cleaning the battery terminals corrected a "solenoid smoking" issue. It's unlikely you have "bad ground" problem but it doesn't cost anything to pull a bolt and clean the termination point.  What you need to do is put a voltmeter across the battery while the engine is at idle. If the voltage is cyclic(it shouldn't be), pull the plug on the V reg and it should stop. So the real question: is it the Vreg or the alternator. You can "full field" the alternator by applying 12V to the field terminal, (it should immediately put full amperage to the battery and the voltmeter should increase - keeping it there more than 60 secs could lead to damage so get your readings and remove the field voltage) or you can pull the alt out of the car and have it tested at any one of the local parts houses. If it passes, change the voltage regulator (whose job is to turn the alternator field on and off which creates the amperage that comes out of the alternator that fluctuates the voltage)  

If that solenoid was smoking I would go aheaqd and replace it after you find your light dimming problem.  My first thought would be to check all the grounds at the lights.  Also, take your solenoid off and wire brush or sandpaper the fender and the back of the solenoid.  

Dimming headlights is a fairly common issue with older Fords. The headlight power is routed thru the switch and when the wiring gets old it wont hold the current required for the lights. The solution is to put in a headlight relay kit. The relays are available thru Mustang Depot. You can also get a kit for halogen lights that includes the lights and relays from several sources like Reenmachine and Mustangs Plus. Inclusion of the relays will solve the problem and also allow you to go to brighter lamps should you choose to do so. The other issue was probably a bad connection.  

Interesting comment. I hadn't really thought about the voltage drop due to resistance in the wiring due to aging(annealing). You don't suppose that there could be similar IR drop across the headlight and/or dimmer switch also & that maybe jumpering around them could identify the drop before going to the relay replacement route you suggest?  

Well my guess JLG is that the solenoid smoking was just a loose contact. The reason I think his lights dimmed is , yes because of the voltage drop thru the switch/dimmer and long wiring run. When he disconnects the battery ground then the alternator is putting out about 14 volts(or so) and his problem is gone because the voltage is up and the lights get enough amps. At normal idle the alternator drops off and system voltage drops back to 12 volts. There is no headlight relay currently, its full power to the switch and back out to the lights, you wont find that in new cars anymore because of the voltage drop and because relays are cheaper then putting in 12 feet if wire I guess. They have long been thinking of going to higher voltage in cars because 12 volts is pretty marginal, I bet they do it in a few more years.  

Hi JLG - Mech is correct on the relays. I got my kit from Mustang Depot and spliced then into the headlight wire on the left inner panel behind my water bag so they are hiden from view (I now fill my bag up outside the car). I also replaced my light and ignition switch. My headlights are now about 30% brighter and I feel much safer (at leased I know people can see me coming now).  

Good points. I wasn't begruding the relay comment. Hoewver, I think the key thing here is that at idle the engine doesn't really spin the alternator fast enough to put out an abundance of amperage needed to run the entire electrical system (early model cars had 38 amp alts) coupled with early mechanical voltage regulators that aren't the best for keeping constant voltage going to the alternator field. The relay route absolutely makes sense to minimize the switch voltage drops that do become an issue as the wiring ages.  Giving more light at all speeds is a clear safety improvement.
JLG  

If you want brighter headlights, but don't want to pay the big price, then build you own relay.  Here's how.
http://midlife66.com/wiring/halrelays.html