• Hi Guest!
    You can help ensure that British Car Forum (BCF) continues to provide a great place to engage in the British car hobby! If you find BCF a beneficial community, please consider supporting our efforts with a subscription.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

electricals ... grrr

Share this page

Nunyas

Nunyas

Yoda
Country flag
Offline
Ok, so I took the plunge last night and installed a new bosch alternater in my '76B. At idle, I measured 14.3V across the battery terminals and 14.5V at the alternater. So, I'm loosing 0.2V between the alternater and the battery... not too bad i guess. However, I'm still plagued with many of the problems I was experiencing prior to the swap/upgrade. If i don't keep the RPMs up over 1500, the car will stall if I use multiple electrical accessories. For example, today during a test drive I found that I could not have my head lights on and use the brakes without the car stalling at normal idle speeds. Also, if I use my windshield wipers at normal idle speed the car will stall. Additionally, when I do use any of the accessories I've noticed that the idle will drop 2 to 3 hundred RPMs, and start running really lumpy. And to add to the problems I seem to be plagued with, the charge light is still coming on (although dimly) when I use multiple accessories.

My frustration/irritation levels have reached a new level for me as I've never encountered problems like this in any of the cars that I've owned previously. So, I'm like shooting blindly into the dark trying to figure out what the deal is. I've a new battery and new alternater in the car. The voltage at the battery is 14.3V and at the alternater is 14.5V.

The PO installed an electronic ignition from Crane (model XR-700) with a points-less distributor. The ignition is also using a "Lucas Super Coil" with balast resistor. I suppose the resistor is 'good' because the car stalls if i disconnect it. Is it possible that some of these ignition components are causing problems when I start using my accessories? I'm not very familiar with how reliable these types of components are normally. Nor do I know how long these parts have been in the car.

Am I 'barking up the wrong tree' by thinking it might be my ignition system components? Or do you guys think it might be time for me to 'bite the bullet' and over-haul the entire electrical system wiring harness? I'm really befudled with what could be the source of what seems to be electrical problems in my B, and would really appreciate any insight that you guys may have in this situation.
 
Hang in there! Time to get the basics first. is your engine ground strap in good shape? all other grounds clean and tight? The ground stap itself could be bad, you might not see this on just a visual inspection, if any doubt replace it. Poor grounds will drive you nuts. they can be very very frustrating.

Mark
 
Mark is absolutely right. I know my Dad once picked up an MG dirt cheap from a guy who couldn't get the electricals sorted. Turned out to be nothing more than a ground strap and we had a nice running MG for a couple hundred bucks! Second story: The MG I drive today was a similar case. My dad bought it from a guy for a couple hundred bucks because he couldn't get the electrical sorted. This one was a little more challenging because it was a bad brake light switch but with the bad switch hooked up, the car wouldn't run. Don't let that discourage you though. A good wiring diagram is all you need. If the ground strap checks out, start by unplugging all the unnecessary running gear from the fuse block. See how it runs. If it runs fine with everything but the ignition/charging system disconnected then you know it is somewhere else. Start by hooking things up one at a time and see if there is perhaps one particular circuit that is causing the problem. Once you've isolated a bad circuit, you can start narrowing it down by unhooking all the accessories on that circuit until you find the one that is causing the problem. That's how I found my bad brake light switch. When I told my buddy that my car wouldn't run and it turned out to be a brake light switch he asked how many months it took me to figure it out. He was surprised when I told him it took hardly any time at all but when you use thourough methodologoical means, it's a piece of cake. Good luck and stick with it!!
 
arg... I consulted my multimeter, and it tells me that I pretty much have a short (0 ohms or extremely close to it) from the engine block to the chassis. So, it looks like the engine's grounding strap is good. Next I checked the ground from battery to chassis and it comes up with 0 ohms as well.

Ah... back to using wiring diagrams... I'm gonna have to break out colored pencils and stuff so I can keep the lines straight without mixing them up. The diagram in my Haynes manual is a pile of spaghetti not only that, but it jumps from '73/'74 N American models to "later N American models" with a '75/'76 UK models diagram in between. I assume i should use the "later N American models" diagram since the UK diagram looks overly simplistic compared to the mess that displayed for the NA cars.
 
[ QUOTE ]
Ok, so I took the plunge last night and installed a new bosch alternater in my '76B. At idle, I measured 14.3V across the battery terminals and 14.5V at the alternater.

Am I 'barking up the wrong tree' by thinking it might be my ignition system components? Or do you guys think it might be time for me to 'bite the bullet' and over-haul the entire electrical system wiring harness? I'm really befudled with what could be the source of what seems to be electrical problems in my B, and would really appreciate any insight that you guys may have in this situation.

[/ QUOTE ]
First, the most basic question. At idle, you measure 14.3 volts at the battery. What does it measure with the head lights on at idle? Under the same conditions, what does the voltage measure at the alternator?

If the starter turns over ok, the main battery connections & grounds are likely to be ok. For some reason, your alternator is either not putting out enough under load, or there is high resistance between the alternator output & the rest of the loads. Also a slipping belt can cause the alternator output to be low under load.

I doubt if there is a problem with the ignition, & overhauling the entire wiring harness isn't likely to be necessary.
D
 
[ QUOTE ]
..., or there is high resistance between the alternator output & the rest of the loads. ...

[/ QUOTE ]

just a thought...but could the ballast resistor be wired incorectly?



Mark
 
eh... been toiling around with it... removed all of the fuses from the fuse box under the bonnet. The car still starts with no fuses in the box, and the headlights still work?!? Incidentally, while was messing around with the fuses my alternater stopped producing power /ubbthreads/images/graemlins/confused.gif I've tried turning everything off and letting it sit for about 15 minutes incase it tripped some sort of internal protection mechanism, but the alternater is still not producing power. With the car running, I'm now getting battery voltage readings. Actually the voltage readings i'm getting now are about 0.3V lower than when the car is off. /ubbthreads/images/graemlins/frown.gif

I really hope i didn't 'fry' the new alternater already... Tried running the engine with the alternater disconnected and measured the voltage at its terminals. The new alternater is now producing 1.8V with nothing hooked up to it /ubbthreads/images/graemlins/confused.gif
 
Nunyas,The Ohm meter test for the condition of the ground strap is not a conclusive statement of its condition.Physically check the ground strap as has been noted by others and make sure it is tight and its mating surfaces are clean.There is also the possibilty that the Lucas coil does not require a ballast resistor you need to consult with the crane's installation instructions,--FWIW---Keoke
 
ah... ok... I don't think i've ever seen a 'normal' grounding strap under the hood of my B. At least, not like the grounding straps that I've seen in the previous two cars that I've owned. I'll have to look into it tomorrow.

As for the voltage readings with the accessories turned on, I remeasured the voltage at the battery with the stock alternater and it's 13.8V engine running no accessories. Headlights turned on the voltage drops to 13.6V across the battery terminals. Headlights on and brakes applied it drops to 13.5V. Headlights on, brakes applied, and wipers on it doesn't seem to change. I tried several different combinations of running the accessories and the voltage at the battery never dropped below 13.5V with the car running. Car off the battery reads 12.5V. The one catch is that I cannot do any of the above if the car is idling at what the manuals say it should idle at. I have to keep the RPMs up around 1500 to do any electrical testing. It was the same way with the Bosch installed too, although the voltages with it installed were all 1V higher than with the Lucas alternater.

On a side note, does anyone know if those reman'ed Bosch alts (from the ford fiesta) have internal protection on them? and if so, how does one go about resetting it? I waited about 30 minutes after it stopped producing power and tried running the car again, but it still didn't produce more than 1.8V at its terminals. I got mine from those folks at 'Auto Express', and would like to avoid having to send it back for an exchange if possible.
 
If you do not have the ground stap therein may be your troubles it must be there!---Keoke
 
It wouldn't be unusual for the voltage to be lower at a slow idle (around 700 rpm). Depending on the pulley ratios, many alternators don't put out much at low engine rpm. The fact that your alternator "puts out" at 1500 rpm (13.5 volts) would indicate that not much is wrong with it. The voltages at the rpm you describe are reasonable. The system is intended to run off the battery with full load & slow idle. If you were going to be running at idle with lights on for extended periods of time, you either need a faster idle or a smaller alternator pulley diameter. I still think that if the starter works, there is not much wrong with the grounding.

As far as the engine stalling, I DO think that your ignition system is "quitting" at too high a voltage. (It should continue to work at a much lower voltage) Possibly due to low voltage at the coil. A coil with a primary resistance of about 1.5 ohms, requires a ballast to reduce it's running voltage once the engine is started. The ballast resistance would usually be around 1.5 ohms. If a ballast IS used with a coil of 2.5 to 3.5 ohms primary, the coil voltage will be too low, especially if supply voltage is low, as during idle or below 1500 rpm, if the lights are on.

To my knowledge, a "Lucas Super Coil" (Sport DLB105) has about 2.6 ohms primary resistance & should be used WITHOUT a ballast resistor. The stock later model coils such as Lucas 16C6, have a primary resistance of about 1.3 ohms primary resistance & should be used with a ballast resistor. IE. Someone may have substituted a non ballast type coil (high resistance) for the original (low resistance) ballasted coil. Try to get some accurate coil primary resistance measurements, & decide if the ballast is needed or is causing the problem. The total resistance of ballast plus coil should be no higher than about three ohms. Whatever combination you use, the coil current should be no more than about four to five amps.

Some alternators will not put out with the wiring disconnected. They rely on the feed through the red light to get the field winding magnetized. Can't say if the new one is damaged. Try working with the old one for a while. I think your only real problem is the engine shutting off when the alternator isn't putting out much. See coil above.
Good luck,
D
 
I'm still looking into my grounding strap issue. However, I did check on my ballast resistor, and coil. The coil that is installed on the car is a "Lucas Super" model DLB102, and I saw reference to it on a website that mentioned it's intended to be used with electronic ignitions and should be ballasted. The resistor that was installed in the car read around 0.6ohms. I had a spare on hand that read 1.5ohms, and I've installed it. It seems to have cured some of my problems, but not all. For example, the wipers will still stall the car if I don't let it thoroughly warm up first.

I'm going to continue looking at grounds and report back later.
 
sounding good, on the right track....perhaps you wiper motor is drawing more than it should?



mark
 
Keoke - I missed your comment earlier regarding the necessity of using a ballast resistor with the Crane XR700. The PO didn't leave me any manuals for any of the after market mods that they've added to the car. However, I did find that someone was gracious enough to publish a PDF of the installation manual. According to what I've seen, the XR700 "requires ballast resistance to limit coil current." So I assume (as much as I hate doing so), that the ballast resistor that I now have installed is of the correct value.

mark - It's possible that the wipers are drawing more current than they should. The PO did some shadey installation of the wiper switch that I'm not sure is entirely correct. Of the switches that I've looked at in various catalogues, they all seem to be rather expensive. Plus I haven't been able to find one for my year that exactly fits my application. '76B w/o OD. It seems that the switches I've seen for '76 are all wiper/OD switch combos. Which would explain why there's a total of 6 possible positions for my switch to be in (off foward and back, low foward and back, and high foward and back). Unfortunately, my wipers' low speed doesn't seem to work at all. When I set to 'low' the wipers will stop on the wind shield at whatever position they're in. I have to switch to 'off' to get them to go to the 'stowed' position.

I found the "grounding strap" lastnight. The PO or the PO's PO had used a 12AWG wire to ground the engine. It was attatched to the engine through one of the cyclinder head bolts and then to the chassis at one of the fuel line clamp screws. It seemed rather brittle and couldn't give me consistant readings on my multimeter. So I replaced it with a 10AWG wire. At the engine I used a valve cover bolt and attached to the chassis where the previous wire was. I'm not entirely satisfied with this installation, and will revisit it in a couple of days. I need to find better locations to attach the cable to the engine and chassis. Incedentally, since I've changed the engine ground, I seem to have a difficult time just getting the car to idle at spec RPMs.
 
Nunyas;

I do not feel that the ground wire guage is adequate for this application. I would secure one from a supplier to the original car's specification.--FWIW---Keoke
 
i agree, i would alse find a good solid ground on the block itself, probly makes no difference.....


I would certainly NOT ground anything near a fuel line. That would just be asking for The Prince of Darkness to Illuminate The Night with his presence.


as far as the wiper switch goes i cant be of much help with that my b has an od with the switch on the shifter, and i am not familar with the wiper switch either having never driven it on the road except to get it home on a bright Sunny day.


Mark
 
hmmm... what about using one of those straps that most modern cars seem to be using. You know, the one that looks like it's made of stainless steal or aluminum. It kind of reminds me of the steal braiding on a hose without the hose in it.

eh... the more i look at my car and compare to the other years of MGBs the more I begin to think that i got one of the worse model years (if not the worst) of MGBs to own... then again, it could be that 'grass is greener on the other side' effect.
 
Nunyas, the part you want as identified in my moss catalog is, "Cable Engine to Ground" part # 332-070. My preferred method of installation is to go directly to one of the starter mounting bolts and then to the closest solid mounting point on the car's chassis. However, the cable must not be stretched tight-FWIW---Keoke
 
I just placed the grounding strap on order along with a couple of other small but important parts. I would have not gotten them if Moss didn't have a $10 minimum order requirement... heh. Oh well, they were parts that I should have had extras of anyways (valve cover gasket, distributor cap, and rotor).
 
Back
Top