Alternator wiring help

[golfobx]

I am trying to wire in a vdo tach. It’s a 1987 with a 19j. There are 2 thick brown wires and the first and second terminals (if looking at the alt from the rear and going left to right). The third is a small brown with yellow tracer.

The small brown with yellow trace goes to the battery icon in the dash.

I assume this is the W terminal I need to use for tach signal? Can I just tap that wire and split it behind the dash to get my signal?

 

[Napalm00]

nope that brown/yellow is the charge indicator, dont tap that for W/tach

Clean the back of your alt and take a pic a few inches further back so we can identify the correct location for you to run a new wire

 

[golfobx]

Here you go

 

[golfobx]

Is that possibly it up on the top left. The spade connector

 

[golfobx]

Spade

 

[RDavisinVA]

Try that spade up to the left and see if it works, but you may not have a tach pulse.
In any event, the 19J is not known for longevity, so in the near future you may be required to swap to an engine that can actually get out of it's own way and have the means to feed your tach.

 

[Napalm00]

Yea it's probably that , thank Lucas for not marking it.

The w connection comes directly off the field wiring , and that looks to be connected to it.

 

[Napalm00]

Forgot to say it's not plug and play you will have to adjust the dip switches and the potentiometer on the side/back of the gauge itself .

If you want it dead on buy a cheap $20 laser tach from Amazon to dial it in

 

[golfobx]

Alright. I started it up today. Gauge does nothing. I tried every combination of the 3 switches.

I get 13.2v to the wire running to that spade. Don’t know if that’s good or not. Maybe that’s not tach out?

Ground is good at 6mv. Power wire is good at 12.7v.

 

[Napalm00]

yep its not it if you are getting 12v. you should be getting a low voltage square wave (undetectable on a voltmeter but not ever seen as 12v)


your alt doesn't have a W terminal, not all alts do, in fact most dont

you can replace the alt this something like this https://www.ebay.com/itm/NEW-ALTERN...v9d7qG4:sc:ShippingMethodStandard!95008!US!-1

its a direct bolt in and has a w terminal .

OR

dont even install a tach, its totally useless on an engine that redlines at 3500rpm ...i have one on my 200tdi and it wasn't worth the install time



EDIT: make sure that alt is clocked correctly before you buy it, im making an assumption that you have a stock setup

 

[Napalm00]

https://www.ebay.com/itm/New-Altern...611932?hash=item51bc8b881c:g:-DUAAOSwkSlbDCpV

70 amp version

 

[golfobx]

Here’s a pic of my current alt

 

[javelinadave]

Here is your answer:
https://forums.lr4x4.com/topic/86753-vdo-tachometer-on-lucas-a115-alternator/

 

[golfobx]

Well there you go. Great find!

however I am in the midst of adding a stereo (4 speakers, amp and sub). Guessing the 45amp is gonna have a hard time keeping up.

with that in mind will the 70amp posted above work for me?

I’m thinking it’s clocked the wrong way round

 

[javelinadave]

Are you going to be driving around with your music at a ridiculous volume? If so then you probably need a bigger alternator. If you're not bustin windows you should be good.

 

[golfobx]

Not blaring. Too old for that. But just want to have some tunes going.

converted to all led lights. Have 4 led fog lights as well.

otherwise it’s stock

 

[javelinadave]

I think you will be fine unless you're winching or running some killer light bar.

 

[Napalm00]

I doubt either of the alternators I posted will work, cases are too big. Thought you had a td not a na .

Id save your money for an engine update

 

[golfobx]

Would a Lucas a127 be a direct fit?

 

[golfobx]

I wired it up as the other thread stated.
On ac current at idle I get about 22mv. When I rev it it goes up to 60 or so. However the gauge still is doing nothing. Is it possible it’s just a bad gauge? I checked ground and power. Both seem fine. I switched the pins every which way. Nothing.

is there a way to test the gauge itself?