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Land Rover Repair/cruise control & tach problems



I try to fix the cruise control system on my Land Rover Disco 1 1995 with automatic transmission.
So far the vacuum pump is working, the hoses are tight and the brake switch is good and the vacuum diaphragm is also good working.
So the mechanical part is OK. So I started with the electrical troubleshooting. The first result showed me, it is ether the steering wheel rotary coupler, the cruise control main switch or the wiring. The broken steering wheel cruise switches are also replaced with a newer used part. Then I replaced the rotary coupler with a newer good use one, but still not working. Then I went to the main switch and did the troubleshooting test as followed. Ignition position 0, cruise control main switch on and steering wheel cruise control set button on. The result should show Bat volt on the pin no. 3 of the Z121 cruise control Ecu plug. But nothing, it showed 0 Volt. So it is the main switch or the wiring. But here my question, does the cruise main switch has to illuminate when ignition is in pos. 0? Then my switch only illuminates when ignition is in pos. II?
Is there an other test to see if the main cruise control switch is working or not?
Any other recommendations?

It also showed me it could also be a bad Park/neutral position switch. If I remove this switch, will it cause any other electronic problems?

An other problem I have is a not working Tachometer. The battery is fully loaded, the generator load is good, the belt is good and the wire connections in the back of the generator are tight. So as far as I know it could be a broken wire and also the phase tap resistor can be bad. But I am not sure how this resistor is look like. Do you have any drawing or picture of it?

Thank you very much


ANSWER: Hi Andy,

The RAVE troubleshooting tests for Cruise Control (CC) are the only ones I am aware of and, as you arrived at TEST C, the results showed that it's either wire faults (RW, W, PB, WY or GR), your Rotary Couplar or the steering wheel switches.

What were your results when you tested the switches?  No trouble with that pesky neutral lockout relay?

I wonder if the tach problem is related to the CC problem?  Check the simple wire on the alt and its spade connector.  I had to replace mine as connection, though tight, was corroded.

Then there is the possibility that another fault (rear lights in my case) were causing strange elec. problems in my dash (radio would sometimes not work, dash lights would not work).  Turns out that a bumper lightbulb holder was the culprit (corrosion). This caused me so much grief.

Solve this tach problem first and see if it negates the CC problem. For phase tap resistor, do a search on K184 in the RAVE and there are several photos there.  

Best of luck,

---------- FOLLOW-UP ----------

QUESTION: Thank you, I will try to fix the tacho first.
Yes I have a problem whit the left back light and the left front stand light. These two lights are connected to the No. 2 fuse and that fuse will always blow out. But not instantly, just after a few minutes.  Do you know something about that?

Thank you


ANSWER: Hi Andy,

take a good look at the bulbholder - it sure sounds like there is corrosion present. Test, inspect then clean them up (brake cleaner), apply dielectric grease (Permatex or CRC) and it should do the trick.

My front sidemarker went and it took my security system with it.  I replaced the bulb but a week later it blew again.  I just replaced the entire bulbholder and never had a problem with it again.  

Lastly, do you have water ingress trouble in your footwell(s)?  This can be a problem with the interior fusebox and in some cases, owners have had to replace the entire fusebox.

Electrical connector problems are a common on these vehicles.

Best of luck,

---------- FOLLOW-UP ----------

phase tap resistor
phase tap resistor  

the back of the Generator
the back of the Genera  

again thank you very much for the info.
In this follow up Question, you should also have received a PDF file to do a test about the not working tachometer. First about that PDF, what does the WS Wire mean cause I only have a yellow brown wire there. And what does that drawing mean in the upper right corner? Does it mean unhook that wire? Cause if I do this test with all wires hooked up, then I have on all three generator connectors loading power of 14.4 Volts. Please see the picture from the back of my generator. Can you help me to understand this test?

An other question, the lights on the side of the rear bumper, do you know what lights these are? I could not find anything about them and they are missing since I bought that car. Do you know if this can cause problems if they are not hooked up?

I missed to answer a question in your first respond, where you asked, "What were your results when you tested the switches?  No trouble with that pesky neutral lockout relay".
Answer: so far i did not test the steering wheel cruise control switches, cause they come in a later test No 4c, and I still try to clear the test 1c cruise control main switch.
That's why I asked you in the very first email, if it is normal that the main cruise control switch only illuminates if the ignition switch is in position II? Can you please check this out on your Land Rover, so I can sort this out?

About the park/neutral position switch, I have replaced it with a new one. I have removed the solenoid in the Gear box, without replacing it and removed the pin from the gear selector solenoid. These wont make any trouble anymore hopefully.
I am looking forward to your answers.
Thank you

Hi Andy,

no problem, I'm glad I can help a fellow LR owner.

That symbol indicates that when testing, the component is disconnected and they you probe the harness connector.  If WS (white/grey) wire not found then probe the wire you have (YB) leading to the phase tap resistor.

As for the lights on the side of the bumper, "bumper mounted side light", there should be wires to these.  They are side marker lights and should be present.  Strange that they are not present and it depends on how they were 'removed' if they cause problems.  Mystery there: why would someone remove them?

As for test 1c - yes, my master switch only lights up when ignition is in pos II.

Hope this helps,

Land Rover Repair

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John McInnis


Land Rover Discovery. I've had most of the common mechanical failures, altenator, water leaks, wiper failure, door/hinge problems, roof rust, floor rust, loads of electrical problems. Remember, I'm not a dealer or a mechanic, just an owner like most of you.


Owner of a Discovery. I've had many mishaps with our Disco but I still like this vehicle. Talk to a fellow LR owner instead of a dealership rep. I'm not in this for the money. I'm just an owner who wants to help others.

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