Thread: 90 Classic charging circuit woes

Installed recon Bosch alternator and new power cable last night and after a couple of trial fitments of spacers behind the pulley to get the belt alignment right, started up and all going well with charging light extinguishing on start up.
Drove to work today and discovered other circuits that drop out when Fuse B2 has been removed- namely indicators! The manual says that these are fused by A5!
So now have no interior lights, door lights, indicators, clock, radio and rear wiper. Engine is also "chugging" at lower revs and won't hold an idle. Stangely the horns now work again and with the hazard lights switched on get right side flashing only. Ah the various backroads and crossovers of modern car circuitry.
So tonight will start the process of chasing down where the short is in the above circuit multitude of circuits.

When I purchased my RRC a couple of years ago the very first thing I did was remove the factory wiring to the battery / starter / alternator. However where I discovered the biggest issue was in the 'bundle' of fusible link wiring encapsulated in a woven fibreglass sheath, rubbing against the inner guard. I've never seen such a concentration of corroded sulphated mess.

Because I was doing a dual battery installation from the outset, I removed all of that wiring, and followed it through the firewall, finding the veritable rats nest of crap from previous owners. Systematically I went about removing every single non-factory wire, then upon seeing that so much of it was butchered, I ended up replacing nearly ⅔ of it, new connectors, relays etc, properly sheathed and cable tied it down.

It took 2 solid weeks of work - redoing every single wire and connector.

It's a real piece of work that old harness. One of the ****test designs, or poorest executions on a semi-sound idea I've ever encountered. No wonder these vehicles suffered from electrical issues. Whoever designed it was no engineer, I can tell you.

Getting rid of the fusible links and using manual reset breakers, and combining / balancing circuits to draw current evenly under a fewer number of breakers, protected with maxi fuse at the distribution point made the whole system more efficient and reduced current draw overall, as well as on the additional 'new' relay-protected circuits which I created for specific short-path runs, some for future population (headlights, driving lights, electric fans, electric water pump, air compressor clutch). The biggest issue was the old engine bay wiring was so butchered and crusty hard old insulation that I felt it was not worth leaving it as it was.

Still, the engine harness needs work, but since that's getting pulled soon, I've chosen to leave it and only patch as necessary.
One of the key 'intelligent' decisions I made at the outset was to run new 0000 B&S earth cables for the chassis earth points on the engine and battery, a new pair of cables from +12v to starter / alternator (000 B&S to starter, 000weldflex to alternator - yes a 90-10 lug is difficult to fit on the back of the factory alternator) and 0000 B&S power feed to the rear compartment mounted battery, plus a modified SBI12 sensing isolation solenoid (replaced with a cole-hersee 400A cont.) This allows me to run a winch at the front or rear of the vehicle (haven't put the rear one in yet, still working on a bar design) and ensure max inrush current handling and current drop is pretty much minimized.

I'm not saying everyone should waste their time and money on doing this, but since I intended to make sure the vehicle had a resilient, robust and waterproof harness I haven't looked back.

Then in October last year, I decided to purchase a new high-output alternator - 120A Valeo / marelli / lucas style.
It died a bit over a month and a half ago, so I put the Denso unit back on, until I do the engine swap (OM606 has bosch 150A). Unit was refunded under warranty -internal winding breakdown.

Then this thread popped up, and I thought - I should go check my circuits.

Here's what I found (and should have understood better from the outset):

1. running the HD cabling is not enough.
2. COOLING the alternator is critical.

I somehow blindly thought that because the alternator was high on the left side of the engine, close to the filter snorkel, that cooler airflow would naturally be available. How wrong could I be!!!
It's nearly the hottest area in the engine bay (crawl under with an IR laser thermometer / FLIR and check it!!)

Some of you may not be aware, but alternator output drops significantly with the increase in temperature. It's not a linear relationship, that much I have found, but it's hard to say exactly what the proportional 'differences' are.

from a measured alternator output at cold start idle rpm of 14.28V, it drops fairly sharply to 13.8v once the engine reaches thermostat opening temp.
when under load @ higher rpm, with no forced airflow over the radiator (i.e. standstill) the voltage drop is down to approx 13.2 - 13.5 depending on operating RPM.

Current output :
engine idle cold Load test with my high-beam headlights, driving lights (all LED) radio on and rear flood lights showed a consistent 53A on the battery monitor gauge (redarc hall current sendor across main battery cable to isolator, not on alternator, as all current feed is via the 0000B&S battery cable to the isolation solenoid terminal)
running hot load test, identical drain, the alternator output was 37A - proof that there was an issue with the engine bay temps affecting the alternator output.

Checking the sheetmetal 'baffle' behind the alternator proved I was heading in the right direction. Because it sits almost directly above the exhaust manifold, it heats up pretty quickly and provides a constant source of radiant heat, which increases the air temperature in the localised region of the rear alternator housing.... Why is this significant you may ask? Because the Alternator draws cool are from the rear of the unit, through the body and is expelled through the front, via the action of the pulley fan. On Hidden fan models, it's the same principle.

Now, in my 16v mercedes, the bosch alternator has a GFR ABS housing cover with a large conduit duct inlet, which the wires to the alternator run through, but the large conduit is one of those aluminized fibreglass heatproof corrugated tubes - like an air preheat hose on old cars... this duct runs to an area of engine bay sealed with a large panel, and is ducted through said panel, to an area where cool air enters. So the alternator always has a cold air intake (it sits directly below the exhaust header, in close proximity) and has never failed, I have removed it to check bearings / brushes and clean out the dust - it's fine....

I thought it was a bit of overkill back when I first saw it, but after having this alternator fail on me in the RRC and seeing that heat is a significant contributing factor in the alternators relatively poor performance and lifespan, I think it's worth investigating a little more, and I may attempt to fit a bosch alternator as an interim measure until my engine swap is complete.

So while that might be a bit long-winded for some, I hope it provides an insight to other contributing factors in the RRC's poor electrical system design and performance, and that simply replacing the cables with a much higher capacity / quality, is not a 100% fix. Finding a way to keep the alternators airflow cool is a priority also, and could very well be a significant contributing/underlying cause to so many peoples failed units.

I'm trying to work out how I can duct some cool air from the holes behind the headlight to the back of the alternator, to see if it improves the situation.

Would be keen to know if other people have noticed how scorching hot these units can get after a good run.