Electrical problem

Technical advice Q&A

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MarkS
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#1 Electrical problem

Post by MarkS » Sat May 01, 2021 3:34 pm

My car is a series 1 4.2 . Last week I had to renew the positive battery lead and other wires going to the terminal post after a shorting out led to insulation damage.
Now I don't seem to get enough current to the ignition. I just get a few clicks on the fuel pump, and a loud tick on the starter button. Could this be an issue with the Alternator Control/voltage regulator...? Looking for clues..

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mgcjag
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#2 Re: Electrical problem

Post by mgcjag » Sat May 01, 2021 4:02 pm

Hi Mark.....yes you could have possibly done alternator/regulator or other damage.....Ideally looking at the cct diagram you need to start isolating wireing.....without engine running you should have 12v to ignition and to fuel pump as per normal........i would look for any other burnt wireing. ...dont forget the fuel pump only ticks till the float bowls are full.....Steve
Steve
69 S2 2+2 (just sold) ..Realm C type replica, 1960 xk150fhc

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christopher storey
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#3 Re: Electrical problem

Post by christopher storey » Sat May 01, 2021 4:12 pm

If you have had a major short, which sounds to be the case, then it may be that the battery is substantially discharged. The click in the starter certainly sounds like that. I should a. check the no-load battery voltage
( should be at least 12 volts and nearer 13.2 if fully charged ) and b. if significantly lower than this , charge the battery as a first step.

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MarkS
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#4 Re: Electrical problem

Post by MarkS » Sat May 01, 2021 4:25 pm

Thanks Steve, I have already renewed all the burnt out wiring, can't see any more damage. Yes, I am aware that the fuel pump clicks until the bowls are full. (I guess I was just pointing out that I got some significant power going to the fuel pump). My electrical knowledge is poor, but i am aware that the voltage regulator/alternator control is not the alternator itself, and I suspect the damage is in that unit (voltage regulator). So I guess what I am asking is whether a damaged voltage regulator would would produce a lack of current going to the ignition/starter..? Anybody familiar with this?

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MarkS
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#5 Re: Electrical problem

Post by MarkS » Sat May 01, 2021 4:31 pm

Thanks Chris. Yes, I thought so too.. But I had my battery on my CTEK charger over night and it seems ok. I tried my spare battery too. Also, I tried boosting it with my powerpack, and I do get more power, -just enough to slightly turn the engine...

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christopher storey
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#6 Re: Electrical problem

Post by christopher storey » Sat May 01, 2021 6:21 pm

Mark : if the battery is well down, it probably will take more than an overnight charge to bring it back up . I don't know what battery(ies) you have but the bigger ones are often of 80AH capacity, so that at say 2 amps charge ( I don't know what the CTEK charge pattern is ) anything up to 40 hours charge may be needed. The other problem potentially is if there has been a substantial dead short, buckled plates may have resulted, and then no amount of charge will bring it back to be capable of producing the 600 or more amps CCA which are needed for a cold start . Keep persevering with charge would be my advice at the moment

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MarkS
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#7 Re: Electrical problem

Post by MarkS » Sat May 01, 2021 6:44 pm

OK Got it, will do. Thanks very much Chris

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abowie
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#8 Re: Electrical problem

Post by abowie » Sat May 01, 2021 10:58 pm

The alternator does not power the starter, the battery does. So while your alternator might be damaged that's not why the starter won't work.

Indeed I'm not sure that shorting the battery out would damage the alternator anyway.

There is a plaited copper earth strap attached on the passenger side to the gearbox mount bolt and to the chassis. It may be that this has been damaged by the short.

As the starter motor takes its earth from the bell housing if this earth is substantially damaged it would limit current to the starter.

Given that the car won't turn over with either a different battery or a booster pack I would check this.

If your short was enough to burn out the large earth wire going from the battery to the chassis I would not be surprised if you battery was cooked as well. Lead acid batteries, as Christopher has said above, do not tolerate being over discharged.
Andrew.
881824, 1E21538. 889457. 1961 4.3l Mk2. 1975 XJS. 1962 MGB
http://www.projectetype.com/index.php/the-blog.html
Adelaide, Australia

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MarkS
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#9 Re: Electrical problem

Post by MarkS » Sun May 02, 2021 12:58 pm

Success..! 'Twas indeed the battery (thanks Chris) .. -needed a double helping of charging. (I must take all my 'spare' batteries to the tip an all..!)
Thanks Andrew, I checked that strap -no damage.
It looks like I got away with fire damage only to the 3 leads connected to the Terminal Post above the Voltage Regulator (marked as the Alternator Controller).
One of these leads is the positive to the battery. I opted not to replace this with the etype copy (which is rather thin and not well insulated), but made up a lead with standard modern thick battery wire.
I did however, replace the Terminal Post with the suppliers copy, mostly because I couldn't find suitably thick insulating washers. They are polypropylene. I don't know what the originals were made from (they are charcoal now), but I suspect their deterioration led to the shorting (and subsequent fire) at the terminal post.

My own fault for running the starter too long (and for installing a hightorque one). But I would urge owners to check these insulating washers at the connection post. I only noticed there was a fire when I saw wisps of smoke coming through the grill at the rear of the bonnet. I could of easily not noticed and jumped out , leaving the car to destroy itself... (sadface)

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