• 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

electrical gremlins

Share this page

jvandyke

jvandyke

Luke Skywalker
Offline
I finally got my rewire job to the testing stage, reinstalled battery and, all is not well.
I have Panel lights, running lights, horn work.
No headlights, no accessories except turn signals (on rear and Left front, not right front)
I have 12 volts at the fuse block, both sides but not behind the dash. What's up with that? I had some "extra" greens in the harness, they're dead too.
hmmmmmmmm


I changed to Neg Earth, have white from tach going to coil's + (well, actually it goes through a ballist resistor first) - to distributor. I haven't repolarized the generator yet.
 
Just took off a LG that I mistook for G that I was trying to power the blower with. Swapped with one of the G. Had voltage but fuse blows right away. Yeah, so the fuse between the white from ignition, and all the greens blows immediately after turning on the key. But the blinkers continue to work which doesn't make sense. I'll have to go through everything I guess. Lucky there really isn't that much to go through on an MKI.
 
I feel your pain. I'm in the process of completely rewiring the Prefect right now. There are no ready-made harnesses or diagrams available so I started with a whole bunch of wire and colored pencils. Actually that was Paint Shop Pro, the electronic version of colored pencils.

Right now I have everything from the front bumper to the driver's seat working and no smoke has escaped...yet. What has worked for me was to complete one circuit at a time and test it before going on to the next. I started with the main feed from the battery since that is required for everything else.

If you can't spot something pretty quickly, you might tryn that approach. First disconnect everything to stop blowing the fuse. Then start adding back, carefully, one circuit at a time. Good luck. You can do it. Just follow the diagram carefully and be sure each wire you connect is the right one and in the right place.
 
Yep, that's the plan. Fuse blows with all switches (wiper, blower, washer, fuel pump) off so I'm thinking I hooked something up stupidly. Must be a short down-stream from the ignition switch. I started with a new harness which is a mixed blessing, it's mostly good because all the wires are there and the correct colors. Down side it's all wrapped up and it was made to cover a range of models as there are more wires in it then the diagram says there should be. I have three extra G behind the dash and a couple extra RW and R where the main hooks into the rear harness. It struck me out of the blue today at work that I didn't connect a ground for the front harness where it goes through the radiator firewall, so hopefully that explains my no headlight issue.

Some questions:
Fuel gauge; G goes to B, GB goes to T, there's also a B. There's three spades on the back of the gauge, two on outboard side connected together, one on the inboard side. I don't see B or T labels on it. Anyone know which spades correspond to which wires?
I assume it didn't matter which wire goes where on the brake switch.
I noticed the ballast resistor was getting hot when I had the key on. I pulled the W off the resistor while I tinkered, is heat build up there normal with car not running but key on?
I still think I'm doing the right thing (wife disagrees) because as the PO had it, the fuse block was disconnected and it appeared everything was basically hot wired although I didn't bother to try and figure out how he did it as I was committed to putting it back the way it was supposed to be with the exception of relays, electric fuel pump, electric washer, and some other minor oddities.
MK1wiring%20labled.jpg
 
He must have bypassed the fuse panel for some reason good bad or other wise in any case I think you need to backup at this point and do a through Inspection of the fuse panel. Replace it if need be. Then start reconnecting the things one at a time checking it with a ohm meter that the lead is not shorted and that is going where it should. Sounds like a PITA but honestly I think it may be the best thing to do as you could end up burning up some wires or worse burn down the car. Make a copy of the drawing you have above and just start high lighting the wires as you go, it should all sort out. I would aso suggest looking close at the control- regulator box pull the 2 screws holding it down and inspect the power busses that are on the bottom side could be shorted and its not the fuse panel. Oh wait this is a newer version not sure if is the same as a Bugeye. Little help people?
 
Okay, I'll start poking around. Fuse block was removed, disassembled (which I don't advise BTW) cleaned, reassembled, pretty simple fuse block, not much to go wrong there. Something is shorted somewhere, has to be.
 
Yes, the fuel gauge should be grounded. You can find the ground spade by checking with your ohm meter. The ground should be also connected to the case. I'd almost bet it is the center one. Of the other two, the one on the E side of the gauge is probably B and the other is F. At least that's how all I have seen worked but they all had screw terminals instead of spades. As a further check, you can check the resistance of each post relative to the ground post. The B post should read around 60 ohms while the T post should be around 100. I'm pretty sure those numbers are about right but the B post should definately show significantly less resistance than the T post.

Also, if we are talking about your MKII, I don't think it would have come with a ballast resistor. In fact, it doesn't show on your diagram. But if it has one then it will usually get hot with the key on. This indicates that the ignition points are closed and drawing current through the resistor. To protect the whole primary ignition, you should disconnect the coil to distributor wire any time you will be leaving the ignition switch on for extended periods but not starting the motor, such as testing the electrical system.

You are absolutely doing the right thing. :yesnod:
 
I poked around a bit tonight, no joy. Ballast resistor is probably on there because it's a Crane coil PS20 I think. I assumed an original coil had internal resistor, PO put this on for the original Allison (that was not hooked up when I got the car). I did disconnect the white to the coil after I found it warm and left it off since.
Fuel gauge is like this, I labeled the wires but don't trust that now. I disconnected it during tested, as well as other things but immediately after turning key POP goes the fuse.
I'm baffled. I dinked around, ran out of fuses.
None of the devices are switched on when I test but who knows. Could it be the ignition switch itself? I resurrected the original (that was in the parts box) just because I thought the little thing deserved it's original switch. I can hook up the other one with out too much trouble to test that theory I guess. Wow, at the rate I'm going I won't need insurance this year.
fuelgaugewiring.jpg



PS I took the control box apart, one terminal had two wires in a blob of solder, not sure if that's how it's supposed to be. Nothing looked shorted or anything. Nice and purdy. Original Ice Blue on firewall behind it. First time off in 46 years? Could be.
Here's a picture.
controlboxinside.jpg
 
Being very eletrickity challenged, I'm hoping to go through and check for continuity between everything that's supposed to isolated from ground and if I find continuity, I've found a suspect. Right?
Check fuse block terminals to ground, then the green wires, then where they attach and on and on and hopefully when my meter drops I've found a short.
BTW I never switched my electric fuel pump wires around but if the switch isn't on, it shouldn't matter, and it has it's own in-line fuse anyway....
I sure hope to work this out soon. The weather is awesome.
 
A hint when faced with a problem resulting in continually blowing fuses, get a circuit breaker that will snap into the fuse holder at your local auto parts store and use this while trouble shooting. It will be cheaper than fuses in the long run. Just start by disconnecting one wire from the fuse block and applying power, if the breaker trips then reconnect that wire and do the next one. Same thing all the way through the harness until you find the short. Then pop out the breaker and install a fuse and you're on your way.
 
I've just never seen that configuration on a Smiths fuel gauge. I wonder if it really came from another car. Those two spades connected together could be a clue though. In the Jaguar XK series, it was common to use the hot side of the fuel gauge to supply other stuff behind the dash. That is probably the case here, indicating that is the B post of the gauge. It wouldn't make any sense to connect anything else to the T post. If that's it then the case itself should be grounded.

I like Bill's suggestion of using a circuit breaker for testing. That would let you test without having to remove everything and start over. The caveat is, be sure you can remember which circuits have been tested. In my case, knowing something is wrong, I would probably start over.

Finally, the ignition switch cannot blow a fuse as it is not fused. It does provide power to the fuse though so something downstream from that fuse is the culprit.
 
I was wondering about a circuit breaker for that fuse connection. Hopefully such a thing is common and I'll come home with one. Trouble is nearly everything that is switched goes through that one fuse so even though there is only two greenies coming off it, it they split and branch and daisy chain all over so, well, let the testing begin.....

Here's the fuel gauge.
fuelgauge2.JPG
 
HMMM, it appears that your DPO cut that hole in the dash and probably did install a gauge from something else. Anyway, I think I am looking at it from its top. If that's the case then the double spade is on the E side and that sort of verifies my earlier guess. The screw connector would be the required ground. I can't tell the wire colors for sure but there should be nothing but black wires connected to it. Also, the photo looks like a green and a black wire connected to that double spade. If so then that is probably your short. The black wire should only be a ground. The only wires connected to the double should be solid green. A hot one will come from the fuse and the other will feed some other device on the dash, possibly a cigar lighter or the heater switch or some thing like that.
 
I'm pretty sure it's an MKI Midget gauge, BE the same? It's not the source of my woes though as I disconnected not know for sure how to hook it up. Something else. I got a 30 amp circuit breaker, auto reset I wired into where the fuse would go. With all wires off fuel gauge it popped immediately. I will play seek and destroy tonight or tomorrow. I might take the day off and spend it with the Midget.

I ran a ground to the fuel gauge's bracket, more for the light I added than any other reason (the bulb holder was the old ignition warning bulb, thus the brown/yellow going to ground and the white in the background as hot) as the gauge has a black ground all it's own, just don't know yet for sure which spade gets which wire, no markings on the gauge that I see. A BE guy should show up and let me know. As it is pictured I'm sure isn't right.

PS yes, that is the top view, dash top tilted down
 
OKay well, I nearly burned her down. Auto rest breaker worked once, I pulled off two of the greens from the fuse block turned the ignition on and no pop, good, walk around front to find smoke, bad.
Quick turn off switch but the damage is done, the one green I left on melted off it's insulation and behind the dash, two greenies are melted together, so now I guess I get to strip the wrap off my $500 harness and start rewiring.....you'd think the circuit breaker would have snapped. It's a 30 amp and there's supposed to be a 35 amp fuse there, thought I was safe. Not. Live and learn.
 
So sorry to hear of your latest misshap. As I understand though, those Lucas fuses that are specified are slow blow. The 30 amp rating is where they blow instantly. They will hold half that current indefinately. At anything over half, they will slowly heat up and blow. The higher the current, the quicker they blow. Actually I doubt that any of those green wires could handle 30 amps for any significant amount of time. We should have been more specific in suggesting a breaker.

Most of the older British cars were woefully underfused. That one fuse feeds the heater, the wipers, the brake lights and the gas gauge, plus any other aftermarket intems that might have been added. In order to have that capacity, it is really to insensitive to deal with a slight overload on one wire that is enough to destroy it rather quickly.

At this point, I would really want to go back to my original suggestion and disconnect everything then add them back, one at a time. Before posering each one, be sure to check for shorts with your ohmmeter.

Also, don't tear up that new harness yet. You said there are extra green wires. You may get lucky and find that the melted one can be replaced with something else, without having to cut into the braid.
 
Tell me if this was stupid or not. At first the extra greens I just wrapped tape over the exposed ends. Then I thought, why not, since they're bullet ends just stick them into a connector (connect them to each other) so, I burned up two of them the whole harness was smoking behind the dash so I'm worried about melting the insulation of their neighbors in the harness? Anyway, off to get some green wire and make my own, I'll leave them outside the harness and if I have a bunch of shorts on other stuff, I guess I start from scratch. Ugh, should have left it alone! It worked, unfused as it was. Now it's fused and I'm burning the car down!
 
Get an ohm meter out and disconnect that battery. wiring can be an absolute nightmare, I would not use a a 400 to 500 Amp battery to test for shorts on a lead rated for maybe 30 amps. Take your time disconnect the battery pull the fuses and use the ohm meter.
 
Yep, battery negative cable is always off unless I'm testing, not leaving it hooked up. My tests are of the continuity nature, I'm checking each wire from end to end looking for continuity to ground where there should be none. I have an old weak motorcycle battery I can hook up for test purposes I guess, not sure how to get a weak (low amp) 12-14volt source besides that though. Heading out to garage now determined to not go backwards this time!!!
 
Just found the green to the wiper motor was melted as well.
Now I have to ask which spade on the motor gets which wire.
G G/B and B, I'm not taking anything for granted anymore, the way things were don't count (I kept like for like during the re-wire but no longer, I want to KNOW how it's supposed to be.

wipermotor.JPG
 
Back
Top