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MG TD TF 1500 - TVS Diodes for SU fuel pumps

I have lots of TVS Bipolar diodes for SU pumps.
They eliminate arcing of the points, need for filing and cleaning as well as fuel pump not working!
If interested email or call me.
Len Fanelli
914 420 8699
Len Fanelli

Installation instructions:
The TVS Bipolar diode is wired across the points and is NOT polarity sensitive.
Connect one end to the rocker blade and the other to the terminal stud,
It fits within the standard non capacitor cover.

Len Fanelli


I am interested in using a TVS diode as an arc suppressor for the pump, however before fitting one I wanted more detailed information on the device. My main concern was its failure mode. I found a datasheet (link is below) which seems to mention that the mode is short curcuit. If that is the case, then just replacing the original suppressor by a TVS will cause problems on our cars in the case of failure.

Checking the wiring diagram, we see that the power to feed the pump is through the auxillary fuse, this is the same feed as the coil. Therefore if the TVS fails (short circuit) the fuse will instantly blow, thereby instantly cutting off the ignition to the engine. However if it fails open circuit we won't be aware of the failure, as the result will be premature wear in the points.

In that case my first thought was to rewire a specific fused circuit to the pump, however, if TVS fails (short circuit) the fuse blows, the pump still fails, if the fuse doesn't blow the pump again, fails, in that case the coil will also overheat and burn out.

Any comments.

J Scragg

The fuel pump and coil feed are not fused, they are fed from the unfused A3 terminal of the fuse block.

It might be a good idea to fuse the pump if you were adding the diode. But what is the use of ignition if the fuel pump is dead.

I added a backup pump, then fused each pump after the selector switch, in that case if the diode was to fail in the short circuit mode you could switch to the other pump and be on your way.

I have the late Dave DuBois converted pump so no arc suppression required.

Tom Ball took over the Dave and is located in OH, he recently rebuilt 2 pumps for me. I picked them up on EBay for a few bucks.

P G Gilvarry

This thread was discussed between 29/01/2023 and 09/02/2023

MG TD TF 1500 index

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