By Mike Cox on Thursday, August 02, 2001 - 07:11 am: Edit

The Tachometer on my Disco I just started going off/on, suspiciously after hitting bumps in the road. I hit another bump and it mysteriously comes back on and acts like nothing happened. I also noted that the headlights start going dim. I checked other systems and I have found that my AC fans are not coming on. I believe they are two different problems, but... Any suggestions on where to check first? Any help would be appreciated, I'm relativily new to Land Rovers.

By mike w on Thursday, August 02, 2001 - 07:19 am: Edit

sounds like a loose connection that will be related to the altenator or the regulator in the altenator has a problem.
good luck

By pk on Thursday, August 02, 2001 - 07:41 am: Edit

There is a small single wire with a push on connector that plugs into the rear of the Disco alternator. It is the signal pick up for the tachometer. The connector works loose and gets greasy. This seems to happen to all Discos sooner or later.

Pull it off, clean it up, tighten it if you can and plug it back in.

pk

By Mike Cox on Thursday, August 02, 2001 - 08:54 pm: Edit

Thanks, I'll start with your suggestions.

By Mike Cox on Friday, August 03, 2001 - 04:25 pm: Edit

Hey guys,

I pulled the connector off and cleaned the blade. I drove to Orlando and it appeared that this did the trick, but as soon as I got in traffic in Orlando, the tach dropped to zero on me a couple of times. It seems to have helped, so I am thinking of putting a new spade connector on. Is there a test for the Alternator/Regulator that I can do just to be on the safe side. I would hate to be in the middle of somewhere and become stranded. Thanks for your help.

By Mike Cox on Friday, August 03, 2001 - 04:25 pm: Edit

By the way, will a bad Tachometer connection cause the lights to dim?

By Steve (Oz93discov8) on Saturday, August 04, 2001 - 12:36 am: Edit

My alternator died recently. The engine missed on acceleration and the tacho wasn't working. The output voltage from the alternator was the same as the battery voltage (about 12.2 volts when it should have been about 13.8 volts). Then the dash light (alternator warning) came on to confirm the problem. Check your alternator output voltage. I had my Lucas replaced with a Bosch (with a 2 year warranty) for $275 Australian (about $150 US probably) and all is well!!

By Mike Cox on Saturday, August 04, 2001 - 04:16 pm: Edit

Checking the voltage is my next meove, where did you get the Bosch Alternator from? I was pricing some of the ones on line and keep seeing prices of around $300-$400 US. Thanks

By Eric Brodis (Broder) on Saturday, August 04, 2001 - 07:57 pm: Edit

Mine died last month and I took it to a local guy that rebuilds them. Turned out that the voltage reg was bad. He replaced it and only charged me $120. Anyone that rebuilds alternators should be able fix it for a lot cheaper then a new one.


eric
Denver, CO

By Steve (Oz93discov8) on Tuesday, August 07, 2001 - 01:14 am: Edit

The Bosch was made in South Africa and the part number is:-

9 120 690 170
K1 14V 55A 20

My engine does not has the serpentine belt - just the standard V-belt pulley arrangement of the old 3.5 litre V8 - even though the engine has been changed over to a 3.9 litre. The only thing I'm not sure about is the max output current of 55A. My workshop manual suggests that the standard (maximum)output should be 65A - maybe my new alternator is a bit under-rated??

By Jon Williams (Jonw) on Tuesday, August 07, 2001 - 04:25 am: Edit

Bad alternator. Just went through that ordeal. My alternator was putting out enough to run the lights-A/C-everything okay, but wasn't putting out enough to do all that plus charge the battery fully and provide enough juice to the ignition coil (so my engine would miss sometimes). So it took me a little while to troubleshoot that. Dealer said when the alternator is bad, the tach usually just stops working. In my case, the tach would drop indicated rpm sometimes (relative to what it normally indicated per a certain speed, etc.). Voltage regulator was okay. Anyway, I put a new alternator on and now everything's fine.

By Mike Cox on Wednesday, August 08, 2001 - 06:00 am: Edit

I checked the Voltage 11.82 volts at idle, in other words.. it ain't working. Since it is still running I decided to do some rebuild pricing. When I told the shop it was a Lucas Alternator, he just smiled and said he'd have to see it before he would give me a price on a rebuild. I translated that to be a "Bend Over" sign. The Tach is still going on and off intemittently. I pulled up the schematics for the Lucas voltage regulator. The tach runs of a PNP transistor on a 12 vdc circuit. It would appear that whats happening is that I am getting inconsistent voltage out of the windings which drops the control voltage on the circuit and killing the Tach. I don't think it's designed that way, but it looks like the tach can work as a barometer to tell you when your Alternator is getting read to go. I'll keep you guys posted on the cost of the rebuild. Thanks for all your help.

By Ron on Wednesday, August 08, 2001 - 06:09 am: Edit

It could be the funky Magnito Marinelli or some crap if yours is an early DI.

Ron

PS someone put a bosch in a RR and others have converted to 160amp delcos yOu need to make a bracket but it did not look too hard

Oh and I think pep boys sells them rebuilt.

By gp (Garrett) on Wednesday, August 08, 2001 - 06:47 am: Edit

my rebuild was about $250. it has the MM core, but i am pretty sure the guts are all Bosch. least i hope so.

By Mike Cox on Monday, August 20, 2001 - 11:47 am: Edit

I realize this thread is old, but just wanted to post the solution. Turned out the Voltage Regulator was bad. Cost to replace was $100.07.
Thanks for all the help you guys provided.