alternator wiring questions

[wdkingery]

Hey guys I've looked all thru my bentley but it's not helpful.. need someone like vince to give me some input.

i've probably got no charge comin from my alternator, and i've installed a new battery but it won't be long before i'm in a jam again.

i think the last owner converted my alternator configuration some kinda way, as there's a plug just danglin (that he allowed the alternator to smash into the radiator and then it subsequently busted on me later )

i've got a very small wire running to the W.

i've got a plug just dangling, with one wire to it.
i've got a big wire running from a screw post to the starter
next to that i've got a small screw post with nothing attached.

my charging light used to flicker, but after installing a radiator i pulled the W wire apart but accident but reinstalled it, but now my charging light doesn't flick anymore.

any ideas? i found a universal reman in the junk yard from an 88 gasser i'm going to go get right now, and it does have a W terminal altho it's unused, and the rest of the wiring looks the same, altho there's something goin to the small screw post..?

any help would be great, as i'm having to trickle charge at night for an alternator

[CRSMP5]

ok.. alt easy...

w is a red/black wire.. this controls the tach/dynamic oil pressure.. if unplugged and car newer then 82 the oil pressure light over 2000 rom will go crazy...

the little blue wire is the alt light.. if unhooked will charge at will/want... needed to excite the alt into charging..

the big wire is red.. it goes to the starter or directly to the batt...

its that easy...

[R.O.R-2.0]

what year is the car in question?

what year car did your used alt come out of?

if your car is 87 or older, i dont think the alt out of the 88 will work right..

i tried a newer mk2 alt in my 85 GTI once, a known good alt, and it would need about 5k rpms to even turn on in my GTI..

[bajacalal]

I think the small screw post should be connected to the blue "exciter" wire. It comes through the alternator LED on the dashboard and provides 12 volts to the alternator when you turn the ignition switch on. These alternators won't start making power on their own, they require a small initial input of 12 volts, so that circuit has to be hooked to a switched 12V+ power source.

IIRC, there were 2 alternator types used for your year, the 60 amp which had a plug connector and a 90 amp unit which used screw terminals- the big one goes directly back to the battery + (via the starter in your case) and the small one is the exciter circuit and needs to be hooked up to a switched 12 volt source (should be powered only when the ignition key is turned to ON or you will drain the battery). And there is the W terminal too but the alternator will work without it.

It sounds to me like someone replaced a 60 amp unit with a 90 amp one and did not hook it up correctly or the exciter wire has become disconnected.

If the junkyard alternator is cheap enough you might consider getting it as a spare but IMO 90% of alternator problems on these cars can be addressed without removing the alternator. The voltage regulator and brush assembly is screwed to the back of the alternator and can be replaced with the alternator still on the car. The connections to the alternator often become corroded. The alternator itself on these cars often isn't grounded well and it helps to directly ground the alternator case to the chassis with a wire.

[wdkingery]

ok! thank you baja. i think that was the problem.. the PO said he changed the voltage regulator, but .. who knows what he did. it's a wonder he didn't kill the damn thing to be honest.

well anyway, i think it was the regulator, but a whole new alt and some drillin (the holes for the cross bolts were too small??) worked it out .. it's a gasser, so you gotta blip the throttle after starting it to get it to charging, but .. the blue wire had just come disconnected, so i think my old one is probably still good. but now i have a functional alt light, and a charging alt! thanks guys! a final WIN here.

now if i could figure how to make a tach for this car i'd love to know my RPMs..

[R.O.R-2.0]

ok! thank you baja. i think that was the problem.. the PO said he changed the voltage regulator, but .. who knows what he did. it's a wonder he didn't kill the damn thing to be honest.

well anyway, i think it was the regulator, but a whole new alt and some drillin (the holes for the cross bolts were too small??) worked it out .. it's a gasser, so you gotta blip the throttle after starting it to get it to charging, but .. the blue wire had just come disconnected, so i think my old one is probably still good. but now i have a functional alt light, and a charging alt! thanks guys! a final WIN here.

now if i could figure how to make a tach for this car i'd love to know my RPMs..

if you cleaned all the grounding points, like on the case of the alt, and the bracket, and even sometimes adding a supplementary ground from the battery to the alternator..

[Baron VonZeppelin]

For whatever reason - the gassers do have smaller bolt / holes for the long lower main support bolt of the alternator. I've drilled out a couple myself.

The easiest and cheapest tach option is to hunt eBay for Diesel tractor or Diesel boat tach. Wire it to the W terminal and its done.

Factory Tbo Dzl Jets had tach clusters. Plug-n-Play.
You have to use CE1 style with upshift light and 2 main connectors on bottom of cluster (85-87 , maybe part of 88). CE2 style has no upshift and just 1 main connector.

85-86 were only years they offered them (TD-GL) in USA.
Canada got them 85-92. But they have Kilo speedometers.
No biggie to swap the speedo tho.
These TD tach clusters get pricey.

Another option is a gasser tach cluster and a dakota digital convertor. But you lose the glowplug indicator. And the CE1 gasser tach will say UNLEADED Fuel Only on it.

[bajacalal]

You're welcome, OP.

I have an '85 turbo diesel Jetta cluster, it only has the big clock and no tachometer. I guess they were a rare option.

But I do have a marine diesel tachometer that works off the alternator W terminal and it's adjustable so it can be calibrated. I don't have it installed in the car yet. I would go this route if you can't find the stock tachometer. Make sure you get one with a high enough range, these are high RPM diesels while a lot of boat stuff will only have a range of like 3000 RPM.