philbobaggins52 Posted April 9, 2022 Author Share Posted April 9, 2022 Hi Phil, I'm not Gary but in the US if your truck came with a charge indicator lamp you need to retain it because it provides 'exciter' current to the field winding of the alternator. This is a light green wire a red stripe (iirc it's circuit 904???) The lamp would be jumpered on the cluster flex circuit with a 512ohm resistor so if the filament breaks the alternator will still charge. Hi Jim, thanks for your input! I reckon I'll transplant the globes and wires from the old harness to the new, plus get onto finishing wiring to the cluster. If this solves the no-stop problem, we can move on! I'll see if the old harness has a resistor too ::)). I'll let everyone know how this goes :) Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 9, 2022 Share Posted April 9, 2022 Hi Phil, I'm not Gary but in the US if your truck came with a charge indicator lamp you need to retain it because it provides 'exciter' current to the field winding of the alternator. This is a light green wire a red stripe (iirc it's circuit 904???) The lamp would be jumpered on the cluster flex circuit with a 512ohm resistor so if the filament breaks the alternator will still charge. Phil - First, you are now on the map. Second, I'm confused. You said your truck is an '86, and here in the States an '86 was the first year where the idiot light configuration wasn't offered. IOW, an '86 US truck wouldn't have a charge light like your harness does. And, it would have only had one in the alternator circuit, which is indeed #904. So where was your truck made? And do you have an ammeter or idiot light in the cluster? As for the diode fixing things, that tells me that your alternator is feeding power back on the excite wire. But it shouldn't. None of the trucks w/o the charge light had a diode and the excite wire goes right back to the ignition switch where it would power the ignition if it was feeding power back. So there's something different about your alternator. But if it works and if a diode fixes the problem, that's good. It shouldn't cause a problem with another alternator. However, a little indicator bulb probably won't pull enough current to run the ignition, so that might fix it as well. Or both the diode and bulb for a belt & braces approach. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted April 9, 2022 Share Posted April 9, 2022 Phil - First, you are now on the map. Second, I'm confused. You said your truck is an '86, and here in the States an '86 was the first year where the idiot light configuration wasn't offered. IOW, an '86 US truck wouldn't have a charge light like your harness does. And, it would have only had one in the alternator circuit, which is indeed #904. So where was your truck made? And do you have an ammeter or idiot light in the cluster? As for the diode fixing things, that tells me that your alternator is feeding power back on the excite wire. But it shouldn't. None of the trucks w/o the charge light had a diode and the excite wire goes right back to the ignition switch where it would power the ignition if it was feeding power back. So there's something different about your alternator. But if it works and if a diode fixes the problem, that's good. It shouldn't cause a problem with another alternator. However, a little indicator bulb probably won't pull enough current to run the ignition, so that might fix it as well. Or both the diode and bulb for a belt & braces approach. 1986 is also the last year a Ford pickup didn't come with a charge indicator lamp in the cluster as standard..... I definitely should have asked how an Aussie truck might differ from the "same" model sold here in the U.S. Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 9, 2022 Share Posted April 9, 2022 1986 is also the last year a Ford pickup didn't come with a charge indicator lamp in the cluster as standard..... I definitely should have asked how an Aussie truck might differ from the "same" model sold here in the U.S. LOL! Yes, the '86 trucks were an oddball that way. Hadn't thought about that. For those that didn't "twig" to what we are talking about, through 1985 in North America there were two ways the dash came - full gauges or gauges with indicator lights for oil pressure and charging. The full gauge package had an ammeter that was "less than informative". In 1986 the indicator light option was dropped, but starting in 1987 there was no option for a full gauge package and all the trucks got an indicator light for charge. IOW, at some point in the 80's Ford realized that the ammeter was a poor offering. It required a shunt, a piece of wire with more resistance than the rest of the wiring, to generate the small voltage that drove the ammeter. But that wire was limited in current capacity and as the output of the alternators was set to go through the roof, if you put a wire in that would handle the higher output you'd never ever see a discharge when the alternator failed. So 1987 they went back to the age-old indicator light, which was the best solution all along. Link to comment Share on other sites More sharing options...
ArdWrknTrk Posted April 9, 2022 Share Posted April 9, 2022 LOL! Yes, the '86 trucks were an oddball that way. Hadn't thought about that. For those that didn't "twig" to what we are talking about, through 1985 in North America there were two ways the dash came - full gauges or gauges with indicator lights for oil pressure and charging. The full gauge package had an ammeter that was "less than informative". In 1986 the indicator light option was dropped, but starting in 1987 there was no option for a full gauge package and all the trucks got an indicator light for charge. IOW, at some point in the 80's Ford realized that the ammeter was a poor offering. It required a shunt, a piece of wire with more resistance than the rest of the wiring, to generate the small voltage that drove the ammeter. But that wire was limited in current capacity and as the output of the alternators was set to go through the roof, if you put a wire in that would handle the higher output you'd never ever see a discharge when the alternator failed. So 1987 they went back to the age-old indicator light, which was the best solution all along. 1987 on clusters all have a voltmeter as well. These seem much more responsive and accurate than the old ammeters ever were. Link to comment Share on other sites More sharing options...
Gary Lewis Posted April 9, 2022 Share Posted April 9, 2022 1987 on clusters all have a voltmeter as well. These seem much more responsive and accurate than the old ammeters ever were. Yep, Ford finally got it right. Link to comment Share on other sites More sharing options...
85lebaront2 Posted April 9, 2022 Share Posted April 9, 2022 LOL! Yes, the '86 trucks were an oddball that way. Hadn't thought about that. For those that didn't "twig" to what we are talking about, through 1985 in North America there were two ways the dash came - full gauges or gauges with indicator lights for oil pressure and charging. The full gauge package had an ammeter that was "less than informative". In 1986 the indicator light option was dropped, but starting in 1987 there was no option for a full gauge package and all the trucks got an indicator light for charge. IOW, at some point in the 80's Ford realized that the ammeter was a poor offering. It required a shunt, a piece of wire with more resistance than the rest of the wiring, to generate the small voltage that drove the ammeter. But that wire was limited in current capacity and as the output of the alternators was set to go through the roof, if you put a wire in that would handle the higher output you'd never ever see a discharge when the alternator failed. So 1987 they went back to the age-old indicator light, which was the best solution all along. If he has put a GM style alternator (most of the one wire ones are) they are famous for back feeding through the idiot light wire. Link to comment Share on other sites More sharing options...
philbobaggins52 Posted April 10, 2022 Author Share Posted April 10, 2022 Phil - First, you are now on the map. Second, I'm confused. You said your truck is an '86, and here in the States an '86 was the first year where the idiot light configuration wasn't offered. IOW, an '86 US truck wouldn't have a charge light like your harness does. And, it would have only had one in the alternator circuit, which is indeed #904. So where was your truck made? And do you have an ammeter or idiot light in the cluster? As for the diode fixing things, that tells me that your alternator is feeding power back on the excite wire. But it shouldn't. None of the trucks w/o the charge light had a diode and the excite wire goes right back to the ignition switch where it would power the ignition if it was feeding power back. So there's something different about your alternator. But if it works and if a diode fixes the problem, that's good. It shouldn't cause a problem with another alternator. However, a little indicator bulb probably won't pull enough current to run the ignition, so that might fix it as well. Or both the diode and bulb for a belt & braces approach. Hi again Gary. Here's what I know about this F100: On the air cleaner box it says date of manufacture was July 1986. It seems the truck (or cab/chassis) was at least partially assemble in Australia (I vaguely recall someone once said these motors were made in Canada - no idea if true). One of the regular stumbling blocks has been that I have yet to find a set of wiring diagrams which truly reflect the colour scheme in my harnesses. The nearest I have got to this is a set which is meant to cover 1984-1986 F-Series/Bronco by Haynes. I suspect that Ford Australia supplied the harnesses, using their own colour schemes and switch components (Bosch Australia is stamped on most electrical components from memory). What I have been doing so far is using a mixture of clues from the Haynes manual, from tracing wires on the original harnesses, from diagrams such as the ones you originally posted to help me, and now I have Kwikwire's scheme plus the new EFI harness I made using colours as close as I could source here. I do plan to draw up a set of wiring diagrams to describe what I have done, for the times when understanding what is what becomes necessary. Wish me luck! I'll take a photo of the dash cluster and post it to you - there's a +/- gauge to show charging/discharging and a charge light. The alternator is a two wire one with internal regulation - so, the B+ connector and the exciter connector. Right now, I think we'll be connecting the bulbs and the cluster into the harness, in part to make sure the oil pressure is ok and to monitor temperature, but also to hopefully solve this won't stop issue. I will post again once we've done this :) Link to comment Share on other sites More sharing options...
philbobaggins52 Posted April 10, 2022 Author Share Posted April 10, 2022 1987 on clusters all have a voltmeter as well. These seem much more responsive and accurate than the old ammeters ever were. Hi Jim! I reckon I've answered your queries in my (lengthy) reply today to Gary's posts ::)) Link to comment Share on other sites More sharing options...
philbobaggins52 Posted April 10, 2022 Author Share Posted April 10, 2022 If he has put a GM style alternator (most of the one wire ones are) they are famous for back feeding through the idiot light wire. Thanks Bill!! I'm not sure about the manufacturer of the alternator, but it seems to be well described by your comment on GM examples! ::)) Link to comment Share on other sites More sharing options...
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