Hi, I just wanted your guy's opinion on this: '78 Fleetwood, 425 of course!

This is especially noticeable at night because the lights are on, but when I start the car everything is bright, the outside and inside lights and the heater is blowing strong, etc. Then, as soon as I drop it into reverse or drive, everything dims quite a bit, I mean it IS noticeable. You can even hear the heater blower motor slow down. When I give the car gas, everything brightens up right away and acts like normal, its just when I am idling in gear and come to a stop. If I use one of the power windows or the locks, it happens even more. Now I know its only a 63 amp, and all older cars "dim" a little when you use the accessories, but I think this is excessive. Now that it is really cold, I have the wipers on, the lights and the rear defogger on. The rear defog really seems to use A LOT of power, when that is on the problem happens even when driving up to 40 MPH, if that makes sense. Basically, if there are only one it two accessories on, the dimming only happens at idle. If there are more accessories on, it happens at idle AND while driving, as soon as I take my foot off the gas to coast, everything dims down until I give it gas to accelerate again, like to pass another car for example. My '79 Fleetwood never did this. GEN light does not come on, yet, and has a brand new battery. No noises coming from that area of engine. I took it to the local place and had them test the alt. and they said it was OK!! However, it was in PARK when the test was being done. What do you think? Belt too tight/loose? Idle set wrong? Alternator just shot?

Thanks

Have the alternator output tested again while the car is in gear, and have the belt tension checked. If both are OK, then it's a deeper electrical problem that's going to take a lot of time and patience to track down.

OK, he said the belt was good, but it was not putting out exactly what it should be. Now, they have two alternators, one is the regular 63 amp and he also has an 80 amp. I heard the 80 was an option, so I if I put an 80 amp in, would I possibly do damage to anything? If you got the 80 amp option, did that also include like heavy duty wiring or something?

OK, the belt was good, but he said it was not putting out what it should. Now my question is, I heard that there was an option in '78 for an 80 amp alternator. The parts store has the regular 63 or the 80 in stock. IF I put an 80 in, would I possibly fry anything or do damage? Did that option also include like heavier wiring or something? I would like to put the 80 in if possible, has anyone done this?
Thanks

OK, the belt was good but it was not putting out what it should. So, I heard that in '78 you could get an 80 amp alternator as an option. Now, if I put that in instead of the 63 amp, would I damage or fry anything? Did that option also include like heavier wiring or can the system handle the 80 amp one without changing anything else? What do you think?

You can substitute the 80A alternator with no problems. It was part of the trailer towing option and was only needed to compensate for the extra electrical draw when towing a trailer.

With what your describing, I'd check your ground and your state of tune. What is your engine speed in drive. I think it's supposed to be 600 rpm.

Sorry the post went up so many times, the computer kept freezing so I hit refresh. Yes, the idle is set right, how do I check the ground? Also, the guy who checked it said "on these cars there is a wire running from the alternator to the starter", should I check that? As long as I won't damage anything, I would like to put an 80 amp in. NAPA has the 80 amp, but they have an 80 amp with a one groove pulley, and one with a two groove pulley, I'm not sure what that means.

Thanks

Don't know about the alternator to starter wire (gotta check the FSM), but the one groove/two grooves pulley thing just means how many belts the alternator can accomodate. You only need the one groove.

Craig

YOU CAN CHECK THE GROUND WIRE from the battery to the frame. The original was aluminum and has a tendency to corrode internally. The other ground connection is at the starter bolt to the frame, but the battery is the one you should be checking. Your main battery to alternator circuit goes through the battery lead to the starter solenoid. The circuit then goes to your ignition switch and from there to the alternator light on your dash ( this may be a secondary circuit ), then to the alternator.

OK, thanks for your help guys, I will check all the grounds, and then if that does not help off to NAPA for the 80 amp alternator.