Alternator dummy light wiring

[Heedwa 6]

Hello 

 

So finally got the mk3 insured and took it out for a spin, it actually ran very well! Thank you to everyone that has helped out on here with the problems I've had over the last year or so. I really appreciate it. 

 

I've noticed that there's no ignition light when I turn the car on, so I wanted to wire the blue wire from alternator to a bulb in the dash. I'm just not sure where the wire from the other side of the bulb needs to go? Will it go to the black cable on the ignition switch or red? How would I connect this? Would it be to the back of the ignition switch or to the plug a bit further down the ignition switch? 

 

I also can't find where the blue wire from the back of the alternator goes behind the dash. I'm guessing it's in the big plug in the back of the cluster dash? 

 

Thanks for all the help, as usual! 

[John Mack 286]

1 hour ago, Heedwa said:

 I've noticed that there's no ignition light when I turn the car on,

 

I'd assume your alternator isn't working then?  Have you checked voltage at battery with engine running?

 

It's pre-facelift/sloping dash you have yes? 

 

 

[Heedwa 6]

Hi, thanks for the message. 

 

That's right, it's pfl with the older sloping dash. 

 

I ran tests on the battery before and after starting. Battery reads around 12.4 before running, and when engine is running at high idle the battery hovers around 13.2, but at normal idle (800rpm) the battery just reads 12.4v.

 

Am I right in thinking it needs to be revving high for the alternator to kick in? 

[sheffieldcortinacentre 610]

If it's not lighting up it won't be charging. It should come on in position 2 & go out once running ( sometimes my need throttle blipping).

Check the bulb is ok, more than likely the problem will be poor contact between the bulb holder & the printed circuit or the main plug & circuit board theyre no 50 years old so getting fragile.

Another problem can be  if the alternator &/or brackets have been painted the alternator can't earth.

A quick check to see if it's charging is with engine running disconnect either main lead from the battery if the engine stalls/cuts out it's not charging.

[Heedwa 6]

Thanks Craig. 

 

I'll check the bulb, is it a 5w bulb? 

The previous owner re routed a lot of the dash lights (indicators flash lights etc) to another spot on the crash pad which he ripped out. So I'm not sure if any of the dash lights work, but will swap the ignition light out with another bulb and take a look. 

 

If I was to cut in a bulb anywhere along the blue cable, say towards the alternator itself and not behind the dash (as a test), and the alternator is working, should the bulb light up? 

 

The alternator isn't painted. 

 

Will also check by removing the battery cable whilst the car is running. Shall I remove the negative cable? 

 

 

[sheffieldcortinacentre 610]

Yes it's a capless bulb like the front sidelights.

 

I'll have to check  how you wire a bulb in.

[Heedwa 6]

I'm guessing it goes from the black cable on the ignition switch to one side of the bulb, and the blue wire from the other side of the bulb all the way to the alternator? 

I could be wrong. I'm not really sure 

[sheffieldcortinacentre 610]

Think so but better to double check in case something gets fried.

[John Mack 286]

Regards the bulb wiring, it needs a feed when ignition is on and it earths via the alternator.  For the alternator to work this wiring must be in place or the alternator will not work.

 

If the wiring/bulb is suspect.....To test the alternator works you could use a test light between battery POSITIVE and the small connector at alternator....this will replicate the dash bulb and therefor should light up before the engine is started but should go off as the alternator self excites and starts to work, as above give it a wee rev.

 

Edited July 29 by John Mack
Spelling!

[Heedwa 6]

I put a light between the small connector on alternator and positive side of the battery, it lit up straight away, and turned off when I started the car. Only thing is, it stays lit even when I turn the ignition off. Guessing this is because of the constant feed from the battery. But does this mean the alternator is OK? 

 

I carried out a multimeter test on the battery, 12.4 when off, 13.2 with the car running, but when the car idles down the battery voltage drops too, back to around 12.6.

 

I also did the test Craig suggested, and removed the negative battery cable with the engine running, and the car didn't stall, which should suggest the alternator is charging the battery? 

 

Just the voltage readings which are confusing 

[sheffieldcortinacentre 610]

Yep the light stayed on because you'd gone straight to the battery rather than through switch.

But it worked like it should so the alternator is definitely ok.

It is strange that it kept going when you disconnected the battery, but you'll probably find that driving it that it will go flat as the radio or fan or lights etc will drain it along with the ignition coil.

[Heedwa 6]

I thought if the car continues to run with one of the battery leads removed, this means the alternator is doing its job? 

[John Mack 286]

From what you've described it sounds like the alternator is in working condition although the voltages could/should be higher.  This could be because of a poor connection/high resistance in the circuit, or maybe the alternator is failing ?

If thou search youtube for volts drop testing, someone will explain it better than I can !

[sheffieldcortinacentre 610]

Yes not sure how unless did you disconnect it after you tried the wire & bulb test ( as this will have switched the alternator on to charging).

 

[Heedwa 6]

So I think the problem is sorted. I opened up the dash and found there was no bulb in the bulb holder for the ignition warning light. Put a bulb in and it lit up with the ignition turned on. When I start the engine the light goes out. I did a meter read on the battery with the engine running, and it gives an odd reading. The voltage slowly rises from 12.4 in increments of 0.03 volts, until it finally reaches around 13.7v. I turned all the lights on and heater and the voltage drops back down to around 12v (is this normal?). Then with the lights and heater off the voltage on the battery starts rising again until it reaches 13.7. 

 

Does all this sound like a healthy alternator doing its job? 

 

Also, does anyone know what gauge the red and the blue wires on the back of the alternator are? Going to rewire the last 10cm or so where they connect to the alternator. At the minute they're a bit of a mess. 

 

Thanks for all your help as usual!