So I've got this splitter which takes 1 signal and splits it into 2 (imagine that).

Anyway, I've been using it backwards to plug 2 instruments into one input on an amp. However, it's connected in parallel, so both lose a tremendous amount of volume. I took it apart and tried to connect them so that the 2 instruments' signals would be combined into 1 series signal, but what I did didn't work.

The 2 inputs both have 2 prongs, and the output has 3 wires. I grounded both of the inputs, grounded one prong of the left input, connected the other prong of the left input to one of the prongs on the right input, and connected the other prong on the right input to the lead wire of the output. The result was that only the right input, which is connected directly to the lead of the output, works. The grounding was sucessful, but there is no signal from the left input.

Could anyone give me some help on how to make the 2 signals combine into 1 series one?

Thanks,
Jacob

Try this:

1- Connect the negative terminal of the output jack to the negative terminal of one of the input jacks.

2- Connect the positive terminal of the output jack to the positive terminal of the OTHER input jack.

3- Connect the remaining terminals of the input jacks together.

This should work but you will have to have an instrument plugged into both inputs all the time.

-Stan

has, i tried what you said, and the result was that the input jack that was directly connected to the positive terminal worked fine, and the other sent a weaker signal to it. Here's a drawing of what I ended up doing, does it look correct?
http://img169.imageshack.us/img169/5975/circuitpz6.jpg

You really need to add a resistor network if you want to mix signals without them interfering with each other, but that loses gain. To do with with no loss you need some active electronics - a simple solution is to make a couple of little buffering preamps like this:
http://www.talkbass.com/forum/showthread.php?t=212647&highlight=make+piezo

Do you actually use both instruments at the same time? If not, why not use a switchable A/B box?