Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Positive to negative woes

Hi,
This morning I worked through the steps to flip my 1960 roadster from positive to nagative ground. I didn't get a spark from the F terminal on the generator, and haven't switched the wiring to the ameter yet (more wires than I was expecting).
The problem is that my new electric fuel pump no longer seems to be working (no ticking). I did manage to briefly short to the chassis while working near the battery after completing my flip. What could be my problem? Thanks

The fuse or if it uses a relay to switch it - could be either but I'd check the fuse first.

Assuming you have an SU fuel pump the electronic (pointless) type are polarity senstive with suffix EP or EN respectively. Some later points types are as well because of the addition of a quenching diode replacing the condenser, which needs to be reversed when changing battery polarity.

This might help
http://www.gomog.com/allmorgan/polarity.html#CHANGING

Hello JCK

A 1960s +4 used to use the mechanical fuel pump on the left side of the engine , so I assume that your electrical one is a later addition.

If you are using a Bendix type pump they are polarity sensitive , one designed for positive earth won't function on negative. The only remedy I know is the replacement option since these units are normally sealed.

The wiring of a 1960s +4 does not have any relays, and only 2 fuses as standard , so check that one not burnt out from your electrical short. if you used a fused feed to the pump.

Thanks everyone. The first thing I did was to check and then replace my two fuses. The pump is brand new. The garage that fitted it for me said that it would work fine it's either polarity. Clearly not the case. I'll check with the supplier.
Meanwhile, I'll put the mechanical pump back into service.

As you are located in the US and just to confirm that you are aware of the difference between British and American fuse ratings. US fuses of a given rating (ie 30 amp) will carry much more current than a British fuse of the same rating.

" The US system rates the fuse based on the continuous load it can handle for a specified period of time w/o blowing, whilst the British system expresses the load at which the fuse will immediately blow."

http://www.mgtoronto.com/pdf/Tech/fuses.pdf

That’s an interesting fact, thanks. The US system sounds ridiculous, by the time the fuse blows your wiring could be well alight. What is the time they allow before the fuse blows?
We live and learn

It may seem so but the cabling current capability should be comfortably in excess of the fuse rating such that wiring may get warm at worst before fuse blows. Note the US is not unique in using slo-blo fuses or breakers to avoid nuisance trips or fuse blows during momentary overloads.

Whilst seemingly a contentious subject fuses and breakers protect in many cases, the actual equipment as well as the cabling feeding it.