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[mautbydecoy]

Hi experts. I'm just coming to the end of building a 1990 350 export Bullet that I got as a box of bits. My alternator has 3 wires - yellow, brown/white and black/white. Any ideas which is which? No doubt I will be back on to pick your brains as I know practically nothing about wiring.

[Les H]

I’ve never come across that colour combination before. If it’s an old open wired stator it is easy to work out the wiring. If you look closely you will see the coils are soldered to the lead out wires near the stator frame edge. Here is the way it works. The 3 coloured wires of the lead out cable are soldered to to 3 different coil combinations. One lead-out wire will solder to only one copper wire. Another will solder to two copper wires and another will solder to three copper wires. So you will have:
3 wires= COMMON.....2 wires= HIGH output power coils.......1 wire is the LOW output coils....... To connect the alternator to a rectifier; connect TOGETHER the leads that are soldered to the HIGH and LOW sets of coils....... The 3 copper wire lead is the COMMON wire and goes separately to the rectifier. Let us know what colours go to what sets of coils please. There is also a way of checking the coils for identification with a multimeter …let me know if you want to check it that way.

[mautbydecoy]

Thanks Les. Combination of sealing stuff and my poor old eyes is stopping me from seeing what wires are connected to what. I think I'll have to try with the multimeter method you mentioned. What do I do? Once I've identified it one way or another I'll post the results.

[Les H]

Hi..Ok sometimes the wire solder positions do get a little gunged up although you can wash it all clean in petrol... Right then turn the multi-meter on and select the very lowest range on the RESISTANCE (Ohms) range. Get a sheet of paper and pen for making a note of which pairs of wires give you the measured readings. Pick up any two coloured lead wires and measure the resistance. Make a note of the reading. Now keep any one wire on the test lead and swap the lead onto another wire and record the resistance again. This will either be higher or lower than the last reading. Then finally swap the test leads so you get the final reading of the last pairs of wire combination. You will now have three sets of readings. The readings will be something like 4.5 ohms......3 ohms… and 1.5 ohms....note these are very approximate readings as I have just made them up but it will give you some idea what to expect. Now the lowest reading pair will be the HIGH output set of coils the middle reading will be the LOW output coils and you will have one pair combination that is gives the highest Ohms reading as it is summing together the High and Low coils in series. This COMMON wire will be obvious from observation and from the readings you have taken and as a check, if you discard the common wire and measure the resistance between the other two it will be give the highest reading as the coils will be summed together in series like this. 3 + 1.5 = 5 Ohms....So in my example: 3 OHMS = LOW O/P wire....1.5 OHMS=HIGH O/P wire. This might sounds extremely complicated but it will take approx 1 minute to establish what each coloured wire is connected to on the alternator. Give it a go and if you are not sure tell us what ohms readings each three pair combinations gives you and hopefully i will be able to tell you what is what. Good Luck.

[Les H]

CORRECTION, I HIT THE WRONG NUMBER KEY:::: "it will be give the highest reading as the coils will be summed together in series like this. 3 + 1.5 = 4.5 Ohms...ETC. ETC"... (Not 5 Ohms)

[mautbydecoy]

Right, now that I've replaced the battery in my meter I've got some readings. Br/w to yellow= 2.3
Bl/w to Yellow= 1.8
Br/w to Bl/w = 0.9

Do these readings sound about right? If so, which is which?

Thanks.

[Les H]

Right the readings are something like I expected...The bl/w to yellow is a little lower than the sum of the other coils, but measuring low resistances can often differ quite a bit to connection corrosion or tarnishing. From what you say, here is what the coil connections are.....COMMON= BL/W.......HIGH O/P= BR/W........LOW O/P= YELLOW.....So to maximise output you need to cross connect the high and low outputs and take them to the bridge rectifier diode on one ac input tag and the other common connection to the other ac tag.....I don't know what wiring diagram you are following but if your diagram shows another version of alternator leads I will cross reference them for comparison, if you say what diagram you are using...must go at the moment dinner is ready...

[Les H]

Just to add, to measure low resistances you should connect the two probe tips together and take a meter reading....You then need to subtract this from the readings of each pair of leads. For example if the test lead short circuit shows 0.4 OHMS (very typical) Then by subtracting 0.4 ohms from your coil readings (0.9...1.8....2.3) we get: 0.5....1.4 and 1.9....NOW you can see by adding 0.5 and 1.4 you will get 1.9 OHMS, which is as exactly predicted so you can see the theory works out nicely....CU

[Les H]

When I had to rush off for dinner I made a mistake with the reply following your post...I should have said: "The BROWN/WHITE to yellow is a little lower than the sum of the other coils (at 2.3 Ohms)".

[Thomas]

Les, thanks for this very detailed and interesting instruction. Leaves only one question for me, what may happen if the leads are connected the wrong way? Just lower output? Or may any part end its life in a cloud of smoke?