jdavidsmi Posted November 23, 2017 Author Share Posted November 23, 2017 Right. Like I said 12.7x is high if the surface charge is gone. So, that reading must have been fresh off the charger. No battery is 'perfect' and I usually see something a little below the ideal for a LA battery. Regardless, there are any number of ways to figure out if the diodes are bad. Try figuring out if the 2G "fire plug" has gone south. I thought that was an easy one to figure out no? https://cimg5.ibsrv.net/gimg/www.ford-trucks.com-vbulletin/2000x1198/80-20171104_171815_3ea9a2879b6917c7e3901d278453fe6aa298c79c.jpg Dave ---- Been having problems with laptop, (Windows 10). got that solved last night. Good Morning and Happy Thanksgiving Anyway the truck sat Monday night, and all day Tuesday with the alternator disconnected. The voltage across the battery read 12.72 Wednesday morning. No change late Wednesday afternoon, still 12.72. Hooked everything back up. This morning it's reading 12.68. just to check to insure the meter was reading close to accurate, I checked with two other meters, ones an old analog and my other DVM. Both reading were right around the same. David Link to comment Share on other sites More sharing options...
jdavidsmi Posted November 23, 2017 Author Share Posted November 23, 2017 Actually on the up to 1987 2G system, the voltage sense for the POS is beyond the fusible links, look at the 1986 EVTM on the website. If it fails, or has a bad connection if the alternator has been replaced with one that has the "fire plug" permanently attached, the alternator will not charge and will promptly destroy itself. Matt blew one on his 86 F150 due to that, fortunately I still had a good one from Darth and was able to help him. I still say, I want whatever it was the engineers at Ford were on when that was designed, it must have been some "dynomite sheet mon". 85lebaront2 What do you mean by "Fire Plug"? Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted November 23, 2017 Share Posted November 23, 2017 Actually on the up to 1987 2G system, the voltage sense for the POS is beyond the fusible links, look at the 1986 EVTM on the website. If it fails, or has a bad connection if the alternator has been replaced with one that has the "fire plug" permanently attached, the alternator will not charge and will promptly destroy itself. Matt blew one on his 86 F150 due to that, fortunately I still had a good one from Darth and was able to help him. I still say, I want whatever it was the engineers at Ford were on when that was designed, it must have been some "dynomite sheet mon". Bill, This is exactly the argument I had with one of the 'Guru's' over on FTE. For someone who posts beautiful color coded schematics of the various iterations of 'hot fuel handling' I think he is stuck when it comes to seeing the obvious. (No knock against him. He is a valuable and knowledgeable contributor) When that stupid charge/stator plug gets corroded and either sets the alternator full field or catches the truck on fire it is a problem. NOTE; I SAID WHEN, NOT IF! Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 23, 2017 Share Posted November 23, 2017 85lebaront2 What do you mean by "Fire Plug"? He's talking about the plug going into the alternator. Ford knew they had a problem so created this: TSB's/2G Alternator Repair. Here's an excerpt: When a generator fails, there are a few failure modes that may cause heat to be produced at the wiring harness-to-generator connector. This excess heat may damage the female terminals on the wiring harness resulting in increased resistance. That is a well-thought out (so they didn't have liability) understatement of a viscous circle, meaning that the heat increases the resistance, which increases the heat, which increases the resistance, ......... until something gives. Frequently it is the alternator, but sometimes the truck. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted November 23, 2017 Share Posted November 23, 2017 He's talking about the plug going into the alternator. Ford knew they had a problem so created this: TSB's/2G Alternator Repair. Here's an excerpt: When a generator fails, there are a few failure modes that may cause heat to be produced at the wiring harness-to-generator connector. This excess heat may damage the female terminals on the wiring harness resulting in increased resistance. That is a well-thought out (so they didn't have liability) understatement of a viscous circle, meaning that the heat increases the resistance, which increases the heat, which increases the resistance, ......... until something gives. Frequently it is the alternator, but sometimes the truck. I'm talking about the charge plug, not the regulator plug. Rectangular, two BK/OR wires about 12Ga. and the Stator wire. The yellow 'sense' wire in the regulator plug comes from the fender relay *beyond the fusible link attached to the BK/OR wires*. So when the plug melts down and the always hot charge wires end up shorting to the case the link blows and the alternator will kill itself pushing power to nowhere, or the whole damn thing catches fire. Link to comment Share on other sites More sharing options...
85lebaront2 Posted November 23, 2017 Share Posted November 23, 2017 He's talking about the plug going into the alternator. Ford knew they had a problem so created this: TSB's/2G Alternator Repair. Here's an excerpt: When a generator fails, there are a few failure modes that may cause heat to be produced at the wiring harness-to-generator connector. This excess heat may damage the female terminals on the wiring harness resulting in increased resistance. That is a well-thought out (so they didn't have liability) understatement of a viscous circle, meaning that the heat increases the resistance, which increases the heat, which increases the resistance, ......... until something gives. Frequently it is the alternator, but sometimes the truck. Gary, that is where the second problem arises. The butt connectors will eventually corrode a little and under load, will cause a voltage drop, but, since the voltage sense is at the junction of the alternator fusible link and the main feed fusible link the built in regulator sees lower voltage and compensates by increasing the field voltage to correct this, under high load, (high beam lights, A/C on with high fan) the alternator ends up at full field and fries itself internally. That's what happened to Matt, the alternator harness had a bad connection and it ended up with the alternator full fielding for about 5 mins, then all the smoke leaked out. Now you know why a number of us have gone to 3G alternators. On most of these trucks a 130 amp 3G from a Taurus 3.8L V6 is a nice near drop-in as it is an axial mount and easy to re clock the housing if needed. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 23, 2017 Share Posted November 23, 2017 I'm talking about the charge plug, not the regulator plug. Rectangular, two BK/OR wires about 12Ga. and the Stator wire. The yellow 'sense' wire in the regulator plug comes from the fender relay *beyond the fusible link attached to the BK/OR wires*. So when the plug melts down and the always hot charge wires end up shorting to the case the link blows and the alternator will kill itself pushing power to nowhere, or the whole damn thing catches fire. I'd forgotten that there were two plugs, but you are right: - C185 & 186: Â Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted November 23, 2017 Share Posted November 23, 2017 Gary, that is where the second problem arises. The butt connectors will eventually corrode a little and under load, will cause a voltage drop, but, since the voltage sense is at the junction of the alternator fusible link and the main feed fusible link the built in regulator sees lower voltage and compensates by increasing the field voltage to correct this, under high load, (high beam lights, A/C on with high fan) the alternator ends up at full field and fries itself internally. That's what happened to Matt, the alternator harness had a bad connection and it ended up with the alternator full fielding for about 5 mins, then all the smoke leaked out. Now you know why a number of us have gone to 3G alternators. On most of these trucks a 130 amp 3G from a Taurus 3.8L V6 is a nice near drop-in as it is an axial mount and easy to re clock the housing if needed. This is why I loop the sense wire of the 3G to the output stud. If the Megafuse blows the alternator doesn't fry itself. Link to comment Share on other sites More sharing options...
Gary Lewis Posted November 23, 2017 Share Posted November 23, 2017 This is why I loop the sense wire of the 3G to the output stud. If the Megafuse blows the alternator doesn't fry itself. Jim - Now I understand. The thing is already booted up, so any loss of "sense" takes it to full-tilt. Bill - The Huck has a 2G and I have a freshly-rebuilt 2G in the attic. So if Matt needs more smoke I'll ship them to where the waters fall. Link to comment Share on other sites More sharing options...
85lebaront2 Posted November 23, 2017 Share Posted November 23, 2017 Jim - Now I understand. The thing is already booted up, so any loss of "sense" takes it to full-tilt. Bill - The Huck has a 2G and I have a freshly-rebuilt 2G in the attic. So if Matt needs more smoke I'll ship them to where the waters fall. Gary, Matt sold "Stolen" to his cousin in Chesapeake several years ago, that's when he found how anemic the V10 is for towing. Using a borrowed trailer to haul the F150 on, he was clear down in 2nd on the 4R100 with 3:73 gears. Link to comment Share on other sites More sharing options...
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