"exciter", Alternator And Flat Battery Problems

Mini Technical Sections Problems, Questions and Technical
1

Hi everyone,

I am having a few problems which hopefully you can help me out with…I am running a 998 Mayfair with stage one tuning.

Here’s my problem. The battery is no longer holding charge and I am getting flatspots around 3000rpm when I do get him running. I have NO exciter/ battery warning light when I start the car, and also the only lights on my dash are the Temp Gauge and Fuel Gauge. “Charlie” was running fine until I started playing, and as I am an amateur, I have probably messed something up! This is what I have done so far:-

I recently changed the Oil Pressure Switch for a mechanical Smith’s gauge as I wanted to see the pressure rather than see a light. I removed the old switch and ran the pipe direct to the gauge, leaving the white / brown cable lose. The gauge works a treat and the oil pressure is spot-on.
I fitted a new dash, but kept all the original off-centre clocks and did nothing to modify the instruments at all.
Removed the spot lamps loom as this was damaged and requires replacing, leaving just the wire from the 4 spot’s loose.

This is what I have done to try and rectify the problem:-
Cleaned the earth connection from the battery.
Replaced ALL bulbs and cleaned holders and connections on instrument cluster.
Checked the charge on the battery, and it is showing around 11v, and doesn’t rise when running engine / revving etc.
Checked connections from alternator, and all reading 11v except for thin Brown / Yellow which is dead.

The only other thing I can think of, is when I removed the spot-light loom, I took a red lead off the fuse box. I think this could be the problem?

Any help is going to be greatly appreciated.

Many thanks!

2

Run a temp wire from batt +ve to the small terminal on the alternator - and run the engine. Does the voltage rise to ~ 13.8 volts?

3

Thanks for the reply. I will have a go tomorrow and let you know what the outcome is, not doing it now as it’s a bit cold and wet out LOL!, and already got drenched today messing around with him!

4

Right then, here are the reading’s I have taken today. Unfortunately, their wasn’t enough power to get him started, so no reading’s are taken with the engine running.

Across the battery with ignition off:- 11.89
Across the battery with ignition on:- 11.53 slowly dropping away

Earth (inside wing) onto Brown / Yellow bottom wire on alternator, ignition on:- 0.03
Same as above onto middle Brown wire on alternator, ignition on:- 10.83
Same as above onto top brown wire on alternator, ignition on:- 10.83

Earth (inside wing) directly onto bottom connection of alternator with plug out, ignition on:- 0.02
Same as above onto middle connection of alternator plug, ignition on:- 0.09
Same as above onto top connection of alternator plug, ignition on:- 0.09

Earth (Inside wing), plug removed from alternator and straight on the plug on brown / yellow wire, ignition on:- 5.26
Same as above but touching the middle cable on the plug, ignition on:- 10.79
Same as above but touching the top cable on the plug, ignition on:- 10.79

Earth (inside wing), plug back in, brown / yellow wire, ignition OFF:- 4.00
Same as above, middle brown wire, ignition OFF:- 9.10
Same as above, top brown wire, ignition OFF:- 9.10

I also checked the multiplug on back of dash, and the circuit board is reading around 9.89, and the cables in the plug are reading the same, EXCEPT, the brown / yellow alternator feed, which is reading between 3.00 / 4.00. The black live feed is reading around 9.00 when touched on the same earth (inside wing).

Sorry about the essay and detail, but as I don’t really understand all this stuff, I thought it best I put it all down.

Cheers.
Kev

5

That is a very complete list of measurements. However, by themselves I don’t know what they really tell you about what is going on.

Though this has been stated in numerous other threads, it is worth repeating here that the ignition (red charge warning) lamp is NOT just an indicator. It is part of the alternator circuit and it must work for the alternator to start producing electricity.

I suggest you make the following test of the warning lamp circuit. Disconnect the plug from the alternator. Push a jumper wire into the receptacle for the small wire in the plug. Run the other end of that wire to an earthing spot on the engine block. Turn the ignition switch to the run position. Does the IGN (red) warning light illuminate? This test is strictly to tell you if the bulb and its wiring are functional.

I know you said the bulbs are ALL new. If the warning circuit works and the bulb is good, the test above should cause the lamp to illuminate. If the bulb does not light up, check first that the bulb really is good. (A multimeter in resistance mode can be used to measure from the bulbs tip to its mounting base. You should measure some low resistance, not “infinite” resistance). If the bulb is OK but does not light up make sure there is 12V on the white wire going to the bulb (when the ignition is on). If you do not have 12V on the white wire you have a supply problem to sort out.

Once you have confirmed that the warning lamp is good and works when the small brown/yellow wire is connected to earth… then you should repeat your battery voltage measurements with the engine off and running. Hopefully you will see an increase of 1 to 1.5V when the engine is running over what you measure with the engine off.

6

To add one small thing to what Doug has said, the warning bulb MUST be the proper type, not a LED, or there will not be sufficient current for initial alternator magnetisation. But that is just for the benefit of others who may have similar problems, as you seem not to have changed the lamp.

7

Thanks for the advice guy’s, but I have decided to let an expert take over the reigns as I am useless!! The bulb is the proper type yes. I am taking him into a respectable garage today to get a full service and EVERYTHING sorted out hopefully. Charged the totally dead battery overnight, so just hope I can get the 10 miles on pure battery power…

8

[sub]10 miles will be NO problem at all once the engine is started. Be sure to post back whatever the mechanic finds.[/sub]

9

Hi chaps…I got the distance no problem, and started up a dream with the fully charged battery, so I know the starting system is going to be fine!

Diagnosis was that the PCB / Circuit board had shot it, causing the loss of a full circuit, so the garage has replaced this and thrown some new clocks in as well for good measure. All is good, all lights working and reading a healthy 14.4v when running! Charlie had also got the wrong carb. needle in, which has also been replaced. So, along with the full service, he should be all good and happy again!

10

that must have cost alot!