British car repair shop in SoMD?
- Thread starter Claff
- Start date
glhs837
Power with Control
Yeah, quite a few problems don't require specialists. Although a buddy of mine who spent quite a few years with British cars (where that thread about abused spouses going back?) referred to Lucas as the inventors of darkness
So, what is the issue?
RPMDAD
Well-Known Member
Yeah, quite a few problems don't require specialists. Although a buddy of mine who spent quite a few years with British cars (where that thread about abused spouses going back?) referred to Lucas as the inventors of darkness
So, what is the issue?
Coming from a previous British biker owner, BSA and Triumphs, have played with Lucas electrical systems before. Haven't played with the car systems.
Claff
New Member
Issue is with the electric fuel pump. The old one clicked merrily away but the innards were wore out and it couldn't pump to the front of the car.
I took the old one (an AC branded unit) out and replaced it with a Facet cube pump. Should be simple: one power wire, one ground, two hoses, one mounting bolt. Got it all mounted up, hooked the wires to the ones used by the AC, but it didn't power on. Switched the ground from the wire to the mounting bolt with the same non-result.
If I hold the wires of the new pump to the terminals of a battery it will power on, so the pump is good. If I plug the old pump into the car's harness it will power on. If I plug the Facet into the same harness I get nothing.
My only guess right now is that the Facet needs a stronger ground than I've provided so far either with the car's harness or the car's chassis. The body is not in great shape so conductivity could be a problem. I can probably run a wire from the pump's ground right to the battery's negative terminal just to be sure, but I don't have a length of scrap wire of the appropriate length yet. If that doesn't work I am at a loss. I hate to admit defeat over what should be a stupid simple solution, but that's where we're at right now. I am certainly open to suggestions; your collective expertise is appreciated.
I took the old one (an AC branded unit) out and replaced it with a Facet cube pump. Should be simple: one power wire, one ground, two hoses, one mounting bolt. Got it all mounted up, hooked the wires to the ones used by the AC, but it didn't power on. Switched the ground from the wire to the mounting bolt with the same non-result.
If I hold the wires of the new pump to the terminals of a battery it will power on, so the pump is good. If I plug the old pump into the car's harness it will power on. If I plug the Facet into the same harness I get nothing.
My only guess right now is that the Facet needs a stronger ground than I've provided so far either with the car's harness or the car's chassis. The body is not in great shape so conductivity could be a problem. I can probably run a wire from the pump's ground right to the battery's negative terminal just to be sure, but I don't have a length of scrap wire of the appropriate length yet. If that doesn't work I am at a loss. I hate to admit defeat over what should be a stupid simple solution, but that's where we're at right now. I am certainly open to suggestions; your collective expertise is appreciated.
itsbob
I bowl overhand
Multimeter would be your friend..
Claff
New Member
'71 MGB with a label under the hood that says "Warning: this vehicle grounded negative earth". Should be "normal" but I suppose this wouldn't hurt to try.
Try...what? In your earlier post you said you already tried both polarity options on the fuel pump wires.
I'm with Bob...you cannot effectively troubleshoot electrical problems without a multimeter handy. Hopefully you have one?....
As for shops around here that work on old Limey iron?..none I'm aware of. (I own a 1959 TR3...)
What about creating a seperate power source for the pump for future repalcement. Get a power source straight from the batt or from your fuse box and use a relay which is activated with the ignition power.
This way you are eleminating any posibility the factory wiring is what you are combating. I replaced the mechanical lift pump on my 1984 Benz with an electric pump and wired it in a seperate power source.
This way you are eleminating any posibility the factory wiring is what you are combating. I replaced the mechanical lift pump on my 1984 Benz with an electric pump and wired it in a seperate power source.
Multi-meter and wiring diagram. 71 is on page 7.
glhs837
Power with Control
Here, just in case you don't have a diagram, wow, the whole car on one sheet
Thats very cool. You should use a meter, I think you can get a cheapie at Ollies or WalMart for $10-$20. http://www.mgexp.com/phorum/file.php?1,file=98144,filename=Wiring_diagram_MGB.pdf
Scroll through page 6 of the PDF covers 70-71.
Guys, if what I'm reading is right, he did not swap leads. changed where the ground grounded, but thats it.
Upon re-reading..I see you are correct. So yep..that MG backwards polarity thing might be an issue here.
Upon re-reading..I see you are correct. So yep..that MG backwards polarity thing might be an issue here.
? huh ... it is Negative Ground ...
..... not like a 1952 Ford Positive Ground
glhs837
Power with Control
Yep, but who knows what whackjob rewiring has happened over the years.
Nearly 100% of British automobiles were positive to chassis/ground/earth at one time and remained so long after the US made negative ground the "standard". Only MG, Rover and Jag survived in to the "modern" era long enough to need to switch to negative ground systems and I don't know off the top of my head exactly when any of them switched over. I know that all of the older MGs I ever worked on were positive grounded. However, from the schematic that Ken provided the link to, its clear that the MGB is still positive to chassis/ground up to '67 and then went to negative ground configuration in '68.
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And of course, the OP says there's a sticker saying "Negative earth grounded vehicle" thats a clue
