Dim lights... then bright lights... then dim again!

[Holshot]

Ever since I've owned this Spider I've had a weird issue with the lighting, hopefully someone has seen this problem and figured out what to do, I'll explain... It seems that when I'm driving with the lights on at night some times the lights, be it headlights, interior lights ect... will be on and have a certain brightness then all of a sudden they get really bright and will stay like that till I turn the car off and then it will go back to the lower brightness. It comes and goes and I love when its in the super bright mode because the headlights are so much brighter and so are the gauges in the dash but it seems to only stay that way for a brief time.

I figured that the car must have a voltage regulator or sorts and maybe that's going bad or maybe a bad ground? The funny thing is is I had the car for about 8 years of so and its always done this. Now on one of my visits to a Fiat specialist here in Baltimore (DiFatta Brothers) I was told that since the car is not driven much that this is the problem and that I need to drive the car more the problem should fix itself, ie. better charge on the battery ect... Now I'm no Fiat specialist but come on. I need to drive it more and that will take car of it. I doubt that is the problem, granted the car only has 29k original miles on it but the last two years alone I've put on 2k miles on the car so I think that's more then enough and it still has not fixed itself.

Any ideas on how to check or fix this problem once and for all or has anyone had a similar problem and fixed it themselves? Any help would be much appreciated!

Kind Regards,
Giuseppe

[So Cal Mark]

need to put a voltmeter on the battery to determine what is happening. Over the years I've seen very few cars fix themselves

[launieg]

Guiseppe, you could have quoted me word for word - same problem exactly. I'll let you know if I ever figure it out!

[kmead]

As always go back to the basics.

How good are the grounds. The strap from the engine to the chassis, from the body to the battery.

Then look at the primary positive side: connection to the alternator, connections to the fuse box, relyas and ignition switch.

As stated above, is the regulator doing its job, it could be allowing an overcharge condition giving you nice bright lights.

[snownsand]

I just resolved this same problem on my '78. The lights would get super bright, the heater fan would sound like a jet preparing for take-off, and the wipers would go so fast you would think they could start flinging off chunks of rubber. But I couldn't replicate the problem in the garage to check voltage, It would only happen while driving. I cleaned and checked all the electrical connections in the charge system but that didn't help. Ended up putting in a new voltage regulator and that took care of it.

[mbouse]

i always advocate adding a grounding strap between the engine block and the inner fender.

[baltobernie]

You could always make a "rolling voltage tester" with a cigarette lighter plug hooked to your VOM. When you're driving look at the meter and see what the system is producing; bright lights and dim lights. My guess is a sticking voltage regulator, but it could be several other things; even a loose charge indicator lamp. But with Fiats, an intermittent ground is always a good bet.

[mdrburchette]

I had the same problem with my 72. After years of trying to figure it out, replacing alternators, voltage regulators, batteries and bypassing original wiring, I ended up swapping mine to the Bosch alternator with internal regulator. Problem solved!

[Holshot]

Thanks guys for all the suggestions... do you think that when the lights get really bright that its not correct and a just effect of the voltage regulator malfunctioning? If so anyway to get them to stay that way permenantly? I love the bright dash lights and head lights, any ill effects ie. frying wires or relays ect... I'm not an electrical specialist so sorry for the newbie questions. Where is the voltage regulator and the grounds I should be looking for?

Thanks,
Giuseppe

[So Cal Mark]

converting the lights to a relay system keeps them much brighter all of the time.

[kmead]

I would add a heavy gauge ground wire from either one of the engine mount bolts (there are four per side) or the rear alternator mount bolt to the bolt for the bumper shock. If you have an early car there are two bumper mount bolts you can use. I would also replace the ground from the battery to the chassis. There should be an existing ground cable from the transmission to the body underneath but these often are damaged over time.

Check the positive wire from the alternator to the starter solenoid as well. I would also look at the quality of the connections of the positive cable at the battery and where it attaches to the starter and fuse box.

Going to a full relay solution for the headlights is a really good choice as well, there are some good how to's both here and on the Xweb as I recall.