Why so many alternator wires?

Post by Robin from France » Subscribing Member » Sat Oct 28, 2017 5:22 pm
Joined: Thu Jan 02, 2014 2:17 pm
Posts: 112
Hi,

I have the usual symptoms on my 2300 petrol '76 flatbed. The ignition light glows gently, and increses in brightness with revs. I've had a look through a number of posts, and have figured out how to test and repair it, and tidy up the wiring which has been cooked by 40 years of exhaust manifold radiation, but my question is simple - why are there so many (redundant) wires?

I've got the original 35 Amp Delco alternator, with two plugs fitted, and five wires. Two are brown, one big (starter solenoid) and one small (redundant), and three other wires are all brown with twin yellow stripes (two to be deleted, one to the dash light). Were the other wires ever used for anything, and why did Bedford make them all the same colour?

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The alternator is charging fine, but, as you can see, the wires are not as good as they used to be!!!
Robin

Re: Why so many alternator wires?

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Post by Phil Bradshaw » Club admin » Sat Oct 28, 2017 11:04 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 4681
Wiring for earlier alternators reflects what was state of the art at the time for battery sensing machines.

The voltage regulator requires the thinner brown wire and wire patched into the alternator warning circuit to function properly.

To achieve this and also run the warning lamp from the auxiliary diodes (diode trio) there's a loop-back of the brown+yellow wire in the harness, hence 3 brown+yellow wires.

Original wiring -

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Your alternator is the UK unit; rear casing on the France unit has no ribs.

Later '2-wire' units are machine sense requiring only the warning lamp wire as well as the thick brown wire to the starter solenoid. Ground wire (black) often isn't fitted which is fine unless the alternator works loose on its mountings.
  • What is real is not the appearance but the idea, the essence of things. Constantin Brâncuși

Re: Why so many alternator wires?

Post by Robin from France » Subscribing Member » Sun Oct 29, 2017 8:54 am
Joined: Thu Jan 02, 2014 2:17 pm
Posts: 112
Thanks Phil for the extra help.

So just to be certain:

I can remove the thin brown wire to the secont BATT + terminal, as it's not needed for my alternator.

I can remove the loop of brown/yellow from the white plug, as it wasn't connected to anything anyway.

I can add a heavy-guage earth wire to the alternator mount if I think it's needed.

If I still have the warning light staying on, I need to test the circuit.

I'd better go find the soldering iron,
Robin

Re: Why so many alternator wires?

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Post by VDUB384 » Club admin » Sun Oct 29, 2017 9:05 am
Joined: Wed Sep 12, 2012 9:01 am
Posts: 1596
Hi Robin, I don't know why you have a thin brown wire to +on the auxiliary battery for split charging you need a 35 amp relay with a 12+ live feed from the starter battery, 12+ from the auxiliary battery which both need to be fairly thick, an earth and a trip wire from the brown/yellow from the alternator or ignition.
Dave
Whilst good maintainece is the best prevention"If its not broken don't fix it."
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Re: Why so many alternator wires?

Post by Robin from France » Subscribing Member » Sun Oct 29, 2017 10:16 am
Joined: Thu Jan 02, 2014 2:17 pm
Posts: 112
Hi Dave,

there's no split charge on this one - it's a flatbed truck. The wires were as original, I think. I've replaced the dodgy connectors and removed the un-needed wires. All cleaned up and re-fitted I still have the IGN light coming on when I rev the engine, so I'm going to check the dashboard end of the circuit.

The wires I'm keeping: (the brown/yellow has been extended with a piece of VW loom in black/white - the best I could find in my wiring box)
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The brown one is folded out of the way:
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Robin

Re: Why so many alternator wires?

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Post by Phil Bradshaw » Club admin » Sun Oct 29, 2017 10:48 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 4681
Low volts incoming to the ignition switch supply can make the alternator warning lamp glow.

Bulkhead connector by the bonnet hinge on the driver side is favourite for dodgy terminals; melted fuse box and worn/burned ignition switch also won't help.

Aim to replace the wire from the alternator to the starter solenoid at some point with thicker cable without any joints in it especially if a 45A or larger capacity alternator is fitted.

Warning lamp only glowing at higher engine speeds usually indicates worn slip ring brushes (common) or faulty voltage regulator (not so common).

For Delco units expect to renew brush holder and brushes when the alternator is dismantled - it's very easy to break them against wear ridges on the slip ring when separating the rear end bracket from the rotor.
  • What is real is not the appearance but the idea, the essence of things. Constantin Brâncuși

Re: Why so many alternator wires?

Post by Robin from France » Subscribing Member » Sun Oct 29, 2017 11:13 am
Joined: Thu Jan 02, 2014 2:17 pm
Posts: 112
OK, thanks Phil.

I've tested the warning light by disconnecting the brown/yellow wire at the alternator and grounding it (is that right?) but no sign of light on the dash. I've removed and checked the bulb, which is OK.

With everything reconnected when I switch on the ignition the IGN light glows (faulty contact in the ign switch?) then goes out as the engine is started. It then comes on again when I rev the engine, brighter than before. Battery voltage shows 12.7 with ignition on or off, and up to 15v when revved.

I've got a couple of spare alternators which I can dismantle. What would be the best source for a new slip ring and regulator? I will renew the heavy wire to the starter solenoid and have a look at the bulkhead connector and ignition switch at the same time.

Oh, and is there a risk of burning something else out if I run the truck locally with a 15v charge? (I need to pick up some wood!)

Robin

Re: Why so many alternator wires?

Post by Robin from France » Subscribing Member » Sun Oct 29, 2017 11:14 am
Joined: Thu Jan 02, 2014 2:17 pm
Posts: 112
Oh, and should I have re-connected the thin brown wire somewhere?

Robin

Re: Why so many alternator wires?

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Post by Phil Bradshaw » Club admin » Sun Oct 29, 2017 12:59 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 4681
'2-wire' unit won't work properly if the alternator warning circuit isn't right, which seems to be the case because the lamp should light when the brown+yellow wire is grounded with the ignition switched on.

Symptoms described also can be due to alternator faults but fix the warning lamp before worrying about anything else!

For the warning lamp check the dash printed circuit where the tabs for the warning lamp bulb holder terminals fold into the holder aperture in the back of the dash.

Tabs folded back on themselves and not entering the bulb holder aperture or cracked copper strip at the folds will kill the circuit.

If the voltage at the battery terminals exceeds 14.5V for long then the battery will start gassing once charged up and eventually will cook itself to death as the electrolyte level drops.

Until the problem is sorted see whether the battery terminal voltage can be maintained around 14-14.5V by switching on the heater motor, headlamps and anything else to hand.

Spares for Delco usually available as Wood Auto or Cargo. Wood Auto SLR3915 for slip ring, VRG3693 for regulator for Delco DN460 fitted to CFs as original equipment.

If you have problems sourcing bits from your side of the ditch then most spares for DN460 are in stock in the club Parts Department either new (brush gear, regulators, bearings etc.) or serviceable used (stators, rotors, casings).

Thin brown wire (battery voltage) isn't required when a '2-wire' unit is fitted. Wire can be cut back and insulated; bend the cut wire back on itself then tape it into the harness to indicate intentional disconnection to avoid "WTF is this for?" when a cut wire is found.
  • What is real is not the appearance but the idea, the essence of things. Constantin Brâncuși

Re: Why so many alternator wires?

Post by Robin from France » Subscribing Member » Sun Oct 29, 2017 2:08 pm
Joined: Thu Jan 02, 2014 2:17 pm
Posts: 112
Hi,

I'm going out to strip the dash, but I've had a look at the spare alternator. You call it a '2-wire' unit, but there are actually four spades - positive and negative on the diode heatsink, and two on the regulator, one labelled IND and the other BAT. I've been connecting the yellow/brown lead to the IND spade, and leaving the BAT spade disconnected. Is that right.

From the broken casing of the other alternator I've removed the electronics for reference. The regulator is a GM 9345333 and the brush holder is unmarked. The heatsink for the diode is a Delco-Remy part.

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Robin

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