VW Electrics main cables

Introduction - Good Connections

Penned by Covkid:

Good connections and good cable are essential for effective charging and starting. However, after 30 years work, the main heavy-guage cables that go from alternator to starter and battery can be subject to deterioration. You need at least 4 metres of new cable do this job - suggested types at the end.

The thickest cable by far is the one between the battery and starter and if you drive a T25 with your main battery behind the drivers seat, you'll realise that its quite a distance between the two. The alternator cable isn't quite as chunky but for this upgrade I replaced both of these cables with the same 25mm fine strand cable. Its just about bendable at that thickness.

Copper cable isn't cheap so prepare for that. Work tidily and you'll get excellent connections as well as a reduced chance of problems in the future.

Cable corrosion

The photo below shows the terrible (although not untypical) state of a cable at the rear of an alternator. This is acid corrosion which can also cause the insulation to crack and break away leaving bare copper wire. Most alternator connections actually terminate in a plug rather than like this and therefore the state of them can easily be missed. The copper within either starter or alternator cable can become brittle and corroded, no matter how far you cut back, and potentially create resistance - reducing the alternator's ability to charge and the starter's ability to turn the engine over. The stands can break too, further reducing the capacity of the cable.

Generally, when things have become this bad, the only thing you can do is replace the cables completely and solder new connectors as and where required. You can crimp (if you have access to oversized crimps) but soldering makes for a more reliable connection and helps seal the cable.

Photo 1: Acid corrosion can take its toll on charging/starting circuit.

This particular engine a 1.9DG and wiring layouts do vary. It also uses a golf alternator rather than a stock one so only has a single nut which holds the main cable. You will need to decide how best to replace corroded cables in your setup.

Replacing cables

I started by removing the old corroded cable on the alternator (above photo) which was not one, but two red cables, twisted around the post and clamped between two washers (not by me!!). This cable doesn't, as you might expect, go directly to the starter terminal as it did on so many v-dubs but goes to a post connection inside the black junction box in the engine bay on the left (see photo below).

Photo 2: Terminal post in junction box in engine bay

I puzzled over this for a while, checking either end to figure out why it was wired this way, and to be honest it still makes no sense unless it was something to do with assembly process at the factory, or that some vehicles had their battery in the back? Towing? Either way, another seperate fatter red wire on that post in the junction box also goes to the starter motor main connector so effectively all went to the starter motor connection anyway - just in a roundabout kind of way!

I gave up musing this one, decided it was daft, and snipped those two alternator cables in that box completely (you can see ends in above photo and what was snipped below) and just ran the new alternator cable straight to the starter terminal with another soldered ring connector. This seemed wholly logical, a more direct route and a lot simpler. I could I suppose replace that single red cable with a heavier one but to be honest the other wire on that post is thinner still. Perhaps if I towed a caravan with leisure batteries, things might be different....

Photo 3: The snipped cable to junction box from alternator

Below, the back of the alternator. As mentioned, mine is a golf alternator (90 amps) and has a single post plus blue trigger wire. I could therefore get away with a really fat cable (handy as thats what I had) but you may need to scale back such ambitions if the cable goes to a plug or spade connector. It doesn't need to be anywhere near as thick as the one I used but does need to be equal to what came off and a good connection. Cable used to wire in a leisure battery would be perfect actually.

Photo 4: On this alternator, I was able to connect using a ring connector and chunky cable

Looking underneath, at the bottom of the pic (below) you can see the two thick cables on the starter - one to alternator and the other to battery. Its important to leave enough room for these cables without stretching them but also routed so they don't foul anything underneath. Running the cable to the battery ended up being a cat & mouse affair. I couldn't be bothered to pull out the old one until such time as I have the vehicle on a proper lift so snipped ends off and ran the new cable as near to exiting run as I could with cable ties until I reached battery terminal. You'll easily run four metres if you go via existing route - less if you ran through rear bulkhead (with grommets) and almost direct to battery inside. Up to you on that - see what works best.

Photo 5: At starter motor from underneath. Alternator cable now goes direct to this terminal instead of junction box as before

Photo below gives you some idea of how chunky the new cables are.

Photo 6: Properly soldered and sealed connectors make for a professional job.

I used 25mm fine strand earth bonding (yes green cable). Colour made no odds to me but you can get it in any colour. Something around the 200amps range is about right otherwise.

I found the beat way to solder the ring connectors on (and mine were sealed at the top with only a small hole, presumably to run the solder in) was to cut back the cable slightly less than you might think, as the sheath melts slightly with heat.

Then rub some flux over the exposed copper cable, slide the ring connector on, warm up with a small blowtorch that jewellers use these days, and run the solder in. Its important not to do this vertically though or you run the risk of running too much solder in which can work its way too far down the cable and make it inflexible - 45 degree angle worked for me.

Once cool, just use some shrink tubing to keep out air and water - remembering to slide the shrink tubing on BEFORE putting the ring connector on.

The difference to starting afterwards was astonishing. Before it was a bit sluggish at times. I'm getting half a volt or so more from the alternator too now as the cable for that was in a hell of a state. They can deteriorate quite badly.