Have an 06 F350 with the 6.0 just under 28k on it (put in service 11/05). I replaced the batteries in Dec not because I was having issues with them, but just because of age. I also keep the truck plugged into a Battery Tender to keep things charged up as the truck can set for weeks without getting driven. Lately though and since I replaced the batteries I've noticed the battery light with turn on/off a few times right after starting but never stays on more than 4 or 5 on/off cycles. I can drive the truck the rest of the day without issue. I first figured I had a bad battery, took the truck back to Interstate batteries to have it tested. As expected both batteries tested out good. After testing we started the truck up and put a voltage meter on the cable coming out of the Alt. it was only putting out about 12.5 volts. Figured the Alt is bad but by the time I got home and retested the alt and it's now putting out 13.6-13.8 volts. So is this an indication the Alt is going out simple because at first start up it's only putting out 12.5 volts? Just looking for a confirmation and thoughts before I got spring for a new one.

Thanks in advance

 

At start-up, the GPR relay is engaged past the time of the wts light. If after say 3 mins, voltage raises to 13.7, all is good.

 

Just a clarification on this and confirmation of the acronyms.

GPR== ???

WTS == WATTS?

Any idea why the light cycles on/off ?

 

GPR= glow plug relay

WTS=wait to start light...tells you the glow plugs are on and to start engine after it goes out. The glow plugs will continue to draw current even after the light goes out... determined by temperature and the GPR. While the GPR is active the alternator output is minimal because of the current draw...this is to protect the alternator.

 

I replaced my alternator at about 38k miles on my truck. I put a new manufacture (not reman) on and took the failed alternator to a rebuilder to have it as a spare. They told me that they saw a lot of these Ford alternators come in for repair...bad slip rings...Ford had a problem with a lot of them and yours might have been one of those like mine. My truck was purchased in September of '05 and yours was 2 months later.

 

Okay.. That makes sense. Now I'm just not sure why the light comes on. As shouldn't the system be aware of the of the GPR, WTS status?

 

Umm.. Wonder if that's what is going on. It's really weird as it only seems to do it when I first start the truck (Cold). After the truck has been running for a while I never see it again. I can start/stop the truck all day long while doing various errands etc. and it will never come on again. Come home park it, start it the next day the light will cycle as mentioned before. I haven't even lift the driveway and most of the time it's done.

 

Well you have replaced the batteries so that should eliminate them as the problem. My guess is that you have some kind of fault with the alternator, even though the DC voltage output is good. If you have a good digital multimeter you could read the AC ripple voltage across the battery posts..if you are getting more then .5 volts AC then I would say you need to take the alternator to an Alternator Electric repair shop and have it gone through. Should cost about $70 or so. Be advised that sometimes alternators test good, but still have an intermitant problem. The alternator shop is the next least expensive option to solving your problem...after the batteries and the alternator it will probably become more time (money) intensive. Also, check the pigtail and the charge wire (big wire) at the back of the alternator (disconect and secure both battery negative terminals before you do this) and make sure they are clean and make secure contact. Good luck.

 

Thanks JakeBrake for the suggestions.

I'm leaning toward something wrong with the ALT, specifically when it's cold. Once it spins for a while and get's some heat in it seems to have no problems. Looking at pricing though and new ones are pretty damn expensive. But it's really only about $60-70 more than a Reman. Umm...

 

I would recommend you take your alternator to a reputable shop and let them go through it...it should be the least expensive route and I would trust that more than most remanufactured units.

 

I would say alt prob has issues as well. I used the GPR abbreviation but your truck actualy has gpcm Glow plug control module. Information is the same, part is just different.

No more than u drive it u make give the alt a swift bump with a piece of wood. Brushes may be sticking on it or communtator rusting up inside alt. I would recommend taking it out for a good run every couple weeks at least if it was mine. More than likely though, prob will eventually get worse and alt will eventually quit all together. If u can get to the small plug in 2 wire connector, make sure it is plugged in good as well and the connection is not corroded.

 

Thanks for the comments. I think I may have figured this out. After more exploration, and troubleshooting. I did some more thinking and realized this all really started happening just after I had a alarm/remote start system put into the truck in Dec.,
when 3 punks on BMX bikes decided to break into my daily driver 1992 Toyota Pickup all caught on 24 hr surveillance.

Yesterday I disconnected prior to starting and didn't have the issue. I tested it again this morning and again problem seems to be fixed. So I think I've ruled what the problem is. Something to do with the alarm/remote start, more than likely the remote start piece of it, but it will be going back to the them to figure out what the hell they did wrong. I spent some good money on the system and believed I was getting it installed at well established dealership. They're primary business is working on Porsche, Ferrari, and other exotics for dealers and customers. Supposed to have been a real high end shop, but it looks like they may understand the exotics, but have a problem with the domestic Ford Truck. At least they didn't hack the hell out of the wires. They don't use butt splices and t-taps. Everything is done with military style splices.

 

Well good luck...hopefully you are on your way to getting it straightened out.