Battery or alternator?

Hello all, electrical question.. 1982 1800 gti. so I'm pretty sure my battery is goosed, it's struggling to start when cold after being left overnight or at work during the day, which is only 15-20 mins drive but once it's going it's no issue and when it's been running for a bit and warmed up it cranks fast and fires straight up. So I'll probably be looking to replace the standard size 063 with a 075 battery, do they fit ok? Looks tight for space as the 075 is a bit longer?

Second, when I'm driving along with the lights off the horn works, with the lights on it doesn't and the lights dim when I press horn button, as well as the water temp light flashing red for a second then going off again. Presumably both use a lot of juice and therefore not enough power to work both at the same time, but with the engine running would the battery be responsible for any of this or is it all down to the charging system? Ie failing alternator? Bad wiring to the battery? I know I also have an earth issue with my instrument cluster which won't help and could be the cause of the temp light flashing .

Cheers, karlos

The horn, switch, wires, relays and connectors all have to be perfect for the horn to work reliably. I 'fixed' mine for a while by just having one connected. Eventually solved with 2 new horns fitted.

Get a cheap multimeter, with the engine running and no consumers should be showing around 14v, with everything on should still be 12.5v+

Not sure about the temp light but sometimes mine comes on when I turn head lights on. Off and back on and no temp light. I've fitted a larger (Diesel sized) batteries to my MK1s, often only a few quid more but another 1/3 capacity in reserve

I would suspect that you have a Grounding issue.
Remove your alternator and have it tested, to remove all doubt, It could be a bad Voltage Regulator, but then it is easier to have it tested off the car, then just guessing.

The Horns use a ground from the Steering rack mount to the steering gear box, it goes up the center shaft to the buttons.  The buttons cause the relay to Pick which provides ground to the Horns.  The Horns have 12V constant to them.

Bad Grounds can effect your Battery and alternator

Have you replaced your main ground from the Battery to the Frame and from the frame to the engine?

If yours are still the OEM for the car they are over 40 years old, they can't go bad?  Replace them.
You can source a new one from werk34.de and vwheritage as well as other places, or you can use 2 off the shelf cables from a parts store.

On my mk1's I ran an addition ground from the engine bracket to the alternator case nut.

Grounds and Vacuum leaks are the biggest issues that I have ever had with Cars.

A DVOM as suggested is going to be a best friend when playing with the car.

Batteries at idle are 12.5-13V.
Batteries with the Alternator running should be 13.75, to 14VDC.

When your grounds are wonky, the Electrical current demons will source other circuits to find the 12V source they use, be it your Speedometer cables, Clutch Cables, or small additional grounds as in your Horn circuits. or your headlights.

The other issue is water migration in to your fuse box.

Yep your DVOM is going to be your friend.

If you haven't upgraded your headlights to Relays, you will be amazed how much Brighter they will be.


Typical horn circuit on Dubs.



See: https://www.vwvortex.com/threads/ground-effects-and-the-repair-of-your-car.5284503/?post_id=71362063#post-71362063

relaying your headlights there are more cost effect kits on the Amazon, Ebay.  just get Ceramic headlight connectors on the ones you buy.
https://www.volkswagenownersclub.com/threads/relaying-your-head-lights.32215/

 

Early-1800 I have a multimeter at home, when I get back from work I'll have a look to see what figures I get. What size battery does a diesel use? I think the temp light is probably a bad earth to the instrument cluster, which I keep meaning to look at but never actually get around to.

Briano1234 funnily enough a guy I work with had a ford escort van which did the same with the lights and horn and he said it was a bad earth from the battery, he told me this not long after making this post.

I've owned the car 17 years and I've only replaced the earth from the alternator to the engine, and all the battery connections do look tired, I'd be lying if I said otherwise . I'll certainly look into replacing them, though my daily is in for a clutch and dmf at the moment which is going to rinse my bank account somewhat

I have had water in my fusebox, the car broke down a couple of winters ago due to the fuel pump relay being full of water, luckily I had a spare in the glove box and have since had a new seal and some welding around the screen which seems to have stopped the leak

And another point, some days it'll fail to crank, so I just leave it and drive my other car, try it the next day and it fires first time with hardly a sign of a struggle, which makes me think there's more to it than just a dodgy battery. Though I still think the battery is bad as well

Regarding battery sizes, 075 will fit, as would I think the larger 100 size, but really, given the uprated Ah rating and starting capacity of modern batteries relative to those fitted in the 1980s, there should be no real advantage over 063. I would steer clear of EFB batteries, designed for stop-start systems, and certainly AGM, which need higher charging voltages to remain healthy.

typ_53b probably not, the battery I have now is a lion 063, and it's just over 5 years old. It's been ok for the most part to be fair.  I'm fairly limited on choice as far as batteries go (I live on the isle of wight) so delivery for a battery is probably not an option. Local we have Euro car parts, which is basically lion, Bosch, varta and I can't remember the fourth option. I'm leaning towards Bosch though as it's middle price wise

Bosch and Varta car batteries are made to identical spec by Clarios, who are the brand holder for Varta automotive batteries. Exide Technologies is another major player in European battery manufacture. Varta and Exide are the main suppliers of oem starter batteries to VW Group. Lion is an own brand of Euro Car Parts, likely sourced from 2nd tier battery manufacturers.

Oh right, I'd never really given any of that a thought, though had read the lion batteries tend to die faster, but given the price it's not hard to see why.

Just put multimeter on battery with car idling.. 13.4-13.5 volts with no load, with heater, lights on full beam and hazards on it was fluctuating been 12 and 12.2 volts, and the alternator was making a bit of a rattling noise, which is good to know.. I guess I'll start with the alternator then. I have a spare but it's anyone's guess as to how good it is.

Get new grounds, as the alternator gets it ground from the bracket that hold tension on it…

While the load from the headlights is because you are running high current through your headlight switch, and relaying them takes the load off the Switch and improves voltage and current delivered to the bulbs

Here is a Quick test for grounds.
https://www.volkswagenownersclub.com/threads/brianos-quick-grounds-test.134637/?post_id=765374#post-765374

Ok, I'll see about sorting out the earths first. Where abouts is the earth from body to engine? I was looking at the wiring last night and my headlight wiring has been hacked up to add the spotlights for a twin lamp grill (not by me) which I did already know, which probably doesn't help. I'll see about getting a picture later.

So for that test, presumably that is with the engine running? What sort of increases would be significant? Excuse my ignorance, I'm fairly clueless about electrics

The main grounds for the engine are located as you are looking at the engine, right side frame horn, between the battery and the air dis, on CIS.  Then it goes from the frame horn to the engine/Transmission.  Either one of the Transmission mounts, or the double studded mounting bolt usually on the upper right side of the transmission

my Thread
https://www.vwvortex.com/threads/ground-effects-and-the-repair-of-your-car.5284503/?post_id=71362063#post-71362063

Which led to:

Then Kammy's thread on the CIS early Cabriolets and things.
https://www.cabby-info.com/electrical.htm#Grounds

Thanks Briano1234 i will have a look at some point, hopefully sooner rather than later. I've looked on werk34, they aren't cheap for what they are, I'm tempted to try making up my own bits, so need to look into that  a bit more too.

That test is with the engine idling presumably?

Karlos1987 said

Thanks Briano1234 i will have a look at some point, hopefully sooner rather than later. I've looked on werk34, they aren't cheap for what they are, I'm tempted to try making up my own bits, so need to look into that  a bit more too.

That test is with the engine idling presumably?

I used 2 off the shelf cables on my rides why because they were shielded.

That test proves that if your car start up quick, then you have a ground issue, If you turn on your headlights while it is running and see @ 13Vdc you have proved that it is a ground issue.  

VW used a unshielded ground cable, it is getting road rash from driving on icy possibly salted roads, it is gettign out gassing from your battery,  when new a Stranded Cables is very conductive, as it get aged, the strands start to stop being a big honing single wire to a bunch of separate wires.  

Bad Grounds and Vacuum leaks are the Bane of cars, specially VW and British Leylands.   

Take your battery cable and measure the voltage drop on it over .5V you have a problen