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That "W" Terminal and a Rev Counter in a 300 TDi query


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I thought it would be cool to have a Rev Counter in my 1995 D90 300TDi.

I bought the instrument, and knowing that the signal needed to come from the "W" terminal on the Alt., I went to connect it up.

But, but... there is already a White/Grey (Hope I'm right about that "Grey" as I'm a little-bit 'colour insensitive') wire attached to that "W" terminal and it disappears nicely into the loom, so not an after-market addition. In the photo attached, the W/G wire has been taken off the "W" terminal.

My Def has no Rev Counter already fitted; it has just the standard Def 300TDi instruments.

So why is that wire attached to "W"?

Scratch head and look at Hynes. No joy there as no "W" wire is shown. More head scratching and search the 'net for a 1994-95 Def wiring diagram. Don't find one. Even more head scratching and contact friend/Auto Elctn. who tells me (from the photo I sent him) that my Alt is a Lucas A127, but he has no idea what that wire feeds.

What to do?

A.) Leave existing wire on "W" and add new wire to feed Rev Counter and hope not to release any Lucas smoke OR

B.) Remove existing wire and see if anything does not work before connecting Rec Counter on its own?

C.) Forget about having a Rev Counter.... no, not really.

Would really appreciate any help with this.

Ron.

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The 'Grey' colour is called Slate so that the abbreviation (S) doesn't get confused with Green (G).

There is a diagram for a Defender with 300TDi, it's on the RAVE range of CDs.

I've looked at version 11 disc 2, which is the earliest I have installed on the PC.

Unfortunately, that's where the good news stops.

Electrical information is split into two sections, the Library and the Diagrams.

The Library gives word descriptions of the circuit, and in 'Starting & Charging' there is no mention of a tachometer feed from the alternator.

The 'Charging' diagram shows a Tachometer, fed via a WS wire from the EGR ECU, and with no wire, or W terminal, from the Alternator.

So that's two differences with what you have (no tachometer but a wired alternator W terminal).

As a matter of interest, does yours have an electrically controlled EGR valve?

Looking at the 'What's on this CD' section of the version 11 RAVE disc, the Owners manuals for the Defender are dated 1999 and 2000, so that 4 year gap to your vehicle probably explains the differences I have highlighted.

There are earlier RAVE discs, but in my experience they need to be loaded into a CD drive for the programme to run.

The CDs that cover the earlier models end at LHP26, and only go to 1989, so don't show either the 200 or 300 TDi engines.

( I see my post crossed with that of PaulMC, the diagram of which explains what I see, but I think my reasoning for the discrepancy still holds good; the diagram is for a later version of a 300TDi Defender.).

Regards.

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David. What ECU ?

It is listed as 'ECU-EGR (D153)'. I rather assumed it's part of the Exhaust Gas Recirculation mechanism.

The diagram shows what I'm looking at, on page 14 of the PDF Red90 links to.

Like I said, I think it's academic really as the diagram appears to be of a 1999 version, whereas the OP has a '95 version.

Regards.

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300Tdi EGR ECU lives under the centre front seat, a friend had a N prefix reg 110CSW which had this fitted. so picking off the alternator 'W' terminal to provide a input signal for a rev counter won't create any problem for the EGR 'brain' if it still functions/fitted.

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Gee Guys. I'm embarrassed that so many of you have bothered to take my wiring query on board.

Embarrassed but also really grateful.

I think that the wiring diagrams provided, whilst very helpful, do not focus in on the detail of my model year (94-95).

My Landy came with an EGR (the ECU for it rolls around the Battery Box.!), but as I have already blocked off the EGR and disconnected the wiring block going to it, I guess I can leave the existing W/S (thanks for the correction) wire off and connect a new wire from "W" to the Rev Counter. That will be a job for Monday; will report how I get on.

My thanks to MMGEMINI, PaulMc, David Sparkes, Red90 and Western. You guys are wonderful!

Until Monday....

Ron.

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Well on Monday (it's now Tues.) I wired up my new Rev Counter to +/- power and the "W" terminal and it worked just great. A little bit high on the revs and as I did not have a precision x-head screwdriver at the time, I could not adjust it down to some 800 or so revs.

A little shopping trip to Maplins tonight got me a nice precision screwdriver set, so tomorrow I'll try to set the new R/C to read closer to reality.

As regards the EGR ECU, I took it out late Sat., and went for an 80 mile drive yest. The Landy seemed livelier, but that may be just in my head as I have had the EGR pipe blocked off this long while.

I also found the W/S wire in the (now redundant) ECU connection block in the Battery box. Think I'll extend that back up into the binnacle to feed the R/C. Means one less wire through the bulkhead.

Once more, my grateful thanks to all who contributed to my query.

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Thank you, Red90. I've had a look at that item, and, as you say, it is really not expensive. I'll order one.

15 or so years ago, I was installing a replacement diesel engine in a boat and I had to borrow a contact tacho to set the Rev Counter in it, as they were outside my budget to buy at the time.

BTW, I have a son living in Calgary. Sadly he's not really a L-R guy :-(

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Which rev counter have you fitted, ? if it's a VDO unit, there is 3 dip switches on the back, numbered 1,2,3. set 1 & 3 up & 2 down, that should get you very close for your engine, them adjust with the screw to fine tune,

Hi Western,

I had to go real cheap on the new Rev Counter as funds are low at present. It's got a 95mm face made by Veethree in India. I'm very happy with it from my testing yesterday. Instant and real smooth response to the throttle with a lovely clear numerals and a black face.

On it, the closest I've got to actual revs is with the DIPs 1 & 3 down and DIP 2 up. That shows 1,400 revs at actual tick-over. I'm assuming tick-over should be around 800 RPM, so, until the Tacho that Red90 referred me to (above) arrives, I think that should be close enough once I get to adjust it with the fine-tune screw.

You might wonder why a 95mm R/C. Well, my plan is to cut out the centre of the existing binnacle and replace it with a suitable material, having holes for the Speedo and the R/C evenly spaced with just one 52mm gauge* high between them, and surrounded by individual warning lights.

I want these separate warning lights as I cannot see the existing bank of lights being mostly hidden by the steering wheel and frequently miss one even though I have raised my seat rail unless I lean forward.

Those warning lights I cannot fit nicely on the revised binnacle will be located on the centre MUD console.

* I plan on having the water temp gauge right in front of me, and move the other gauges over to the Mud console. Any thoughts on this?

Thank you for all your kind advice/assistance.

Ron.

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