fuse confusion

Dell (WA) · Apr 18, 2013

Guys........gotta head scratchier. Trying to gitt my "midlife crisis" (1976 MGB) to run. Jeeze, I'm missing all the NICE WARM WEATHER (frown) I have a 17-amp fuse (yeah, limies drive on the wrong side of the road too) As best as I can tell from the smudged up drawings, it is power to the electrical (SU) fuel pump. Using a "test-probe", I have lite on one side of the fuze and NONE on the other side of the fuze. (blown fuze, right???) ...except... when I disconnect the fuze from the fuze block, (to the pump) I now have lite on BOTH ends of the fuze. Once I clip the fuze to the clippies, NO LITE on the electrical fuel pump side. I bought some NEW fuzes (15-amps) and gitt the SAME reaction.

BTW, the fuel pump is NOT pumping. .........the STUMPED Dell

Bob Harvey · Apr 18, 2013

Bad / corroded ground on the pump ? Didja get your e-mail working yet ?

Waltmo · Apr 18, 2013

Problem may be up stream from the fuse block.
Maybe enough power to turn on your test lite but not enough to run the fuel pump. This could drain your voltage down so much it won't turn on your test light when your pump is connected to the circuit.
I would try a test lead from the battery to the fuse on the end before the pump so it will be fused if there is a short circuit. hth WaltMo

Dell (WA) · Apr 18, 2013

Bob..........yep, NEW email is [email protected]. Mighty Microsofty strikes again.........Dell

Roger in Iowa · Apr 18, 2013

I agree with Walt. You may have voltage to fuse but not the amps to drive pump or blow the fuse. Check up stream.

tracman · Apr 18, 2013

I suspect ypou may have a lamp or relay on the same fuse that' floats' to positive when the fuse is pulled out. As was said you still may have a bad ground problem. Is the pump in the tank or external to the tank?

Anonymous-0 · Apr 18, 2013

Times like this I tend to grab my AMPROBE ohm meter. Check resistance across the fuse block and across fuel pump to grnd.

HTH John,PA

Dell (WA) · Apr 18, 2013

tracman.......the pump is EXTERNAL to the tank. I HATE laying on the ground with the rain drippin' up my nose. It takes all the "curl" outta my mustache .......curly Dell

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Dell (WA) · Apr 18, 2013

John.........fuel pump is next to right rear wheel. Well you know a GOOD fuze is "zero" resistance ...but... I'll try across the fuze block WITHOUT a fuze in it. ........Dell

tracman · Apr 18, 2013

Dell can you pull the connector off the pump and repeat the fuz /lite check?

8N-Bob · Apr 18, 2013

Sounds like a bleeding ground to me also.

Unplug the pump and with out the fuse see if there is voltage on both sides. If yes start pulling other fuses and when the voltage is gone you know what circut you have a bad ground in. Also is the fuel level sending unit on the same circuit that could be your problem there also.

Lots of Luck
Bob

Anonymous-0 · Apr 18, 2013

I bought a 1978 MGB 10 years ago that is my mid life project. Bright orange with a removable hard top. My wife wouldn't ride with me on a Harley so the MG was my next choice. I bought one just out of high school but sold it when I built this house. Post a picture of yours when you get a chance, I enjoy seeing other posters projects.

Anonymous-0 · Apr 18, 2013

I had a problem once with a 3phase (3fuzes) block with one fuse not working when installed. Came to find out that one of the fuse (clamps) contained in the fuse block was burned off the screw at the outfeed wire connection. 'Nuff to drive a guy nutty on a 160 deg. roof.

Glad to hear about your new email address. Gee, I am lost when I cannot count on a guy for moral support, from time to time.

John Old Maytag repairman.

Ronnie Graves · Apr 18, 2013

unless someone bypassed it car has a safty switch
to kill power to the pump , when you switch on the power (mains as they call them )the pump powers up and fills the carbs , then when you start the engine the oil pressure comes up an turns on the pump ,and it only runs when there is demand pressure drop at the pump , also the fuse is powering the relay located somewhere under the "boot"

Dell (WA) · Apr 19, 2013

Ronnie........yeah, there is an "up-set" relay behind the dash panel that kills all the electricity when you have an "accident". Remember, my midlife crisis was running last fall when I parked it. .......Dell

pconnie · Apr 19, 2013

have had mgbs since 72..still have 5 of um..once 65 quit ..fuel pump..found a burnt out tail light..replaced it and lo and behold pump started working..english wiring..also once it quit and it was the connection on right front frame behind tire..worked loose..hope you get ur going so you can enjoy..i had one when in denver..notin like mountain cruising..beautiful vistas..switch backs were awesome..good luck

barefoot · Apr 19, 2013

dem Brits do some funny wiring. They run the hot wire through the system to the switch and from there to ground. So a short in the wire will cause a completed circuit. Are doing a continuity test or a voltage test. If you're doing a voltage test the I'm going to suggest take the 4 fuse block off the car and clean it good. "Bright and Tight" I have a couple of those LBC's (still own 3)that have given me headaches. I may have an extra fuse block if your's is beyond repair. I have a pile of parts.

ASEguy · Apr 20, 2013

I would try running a fused jumper wire from the battery to the downstream side of the fuse to see if that powers up the pump. If it works I would look for a short to voltage. If not, check the ground side with a test light, not an ohm meter. Gerard

fuse confusion

Dell (WA)

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