I have a Malibu Low Volt 300 watt timer. The power & GFI are good. I checked the 10 watt LED bulbs there are only 6 of them. Could the problem be That I should have a timer for LED's only ?

Malibu ML300 has 120 volt input and 12 volt AC output
They make a photo eye for the timer... wiring is changed a bit... will work on ML300 if timer has A-B-C wiring terminals
http://waterheatertimer.org/Malibu-power-pack-stopped-working.html#wire

You can use a 120 -> 12 volt ac transformer that is rated for 300 watts... and connect in-line photoeye on the 120 volt side.
http://waterheatertimer.org/How-to-install-and-troubleshoot-photo-eye.html
http://waterheatertimer.org/Reverse-photo-eye-so-it-turns-on-at-daytime.html

Gene
Water Heater Timers Save Money

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You posted under Malibu Power Pack.
If you have different timer, then instructions below will not fit your question.

1) If I understand correctly, you can manually turn malibu low-voltage lights on-off but timer is not working.

2) 'Harry' wrote fixya with a work-around. He bought cheap plug-in timer. Set power pack to override and then plugged power pack into cheap timer.

3) Harry also said he has 5 year warranty and was negotiating with malibulights.com for refund.
No word how that came out.

4) Other than Harry's solution, I have not been able to find repairs and parts for power packs.
Hours of searching Malibu, Intermatic, ebay etc turned up a few folks who took their power pack apart, but nobody reported they fixed a power pack once it goes bad.

5) The best I found are tips for next power pack that might save money:
The reason I add these tips now, before your power pack needs replacement is some fella wrote-in.
He bought 500 Watt power pack to replace 300 Watt > thinking bigger was better.
Power pack burned out. Here's why:
a) Match wattage of bulbs with wattage of power pack
-15 each X 20 watt bulbs = 300 watts, so install 300Watt power pack
b) Installing a 500W power pack on 300W of bulbs will burn out bulbs and power pack.
c) Replace bulbs as soon as they burn out or other bulbs will burn out and power pack will burn out.
d) When working on bulbs, unplug power pack or it may burn out.
http://www.malibulights.com/guides_support/low_voltage_planning_guide/select_your_power_pack

6) Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on timer or any do-it-yourself project.
Fixya is always less expensive than a service call.

Trippers for low voltage timers are not available at Malibulights.com or Intermatic, or ebay.
That explains why folks ask power pack questions on fixya instead of finding results at the manufacturer's website.
New Malibu power packs are electronic and not mechanical

'Harry' wrote me about a work-around for lost trippers.
He bought ordinary 3-prong wall timer, and then set malibu power pack override to ON, and then plugged power pack into wall timer. 3-prong timers sell for $10 at Walmart and Target.
http://www.amazon.com/Woods-59204-Weather-Outdoor-Repeats/dp/B0014WRNNK
http://www.smarthome.com/56006/Woods-13571-Indoor-and-Outdoor-24-Hour-Mechanical-Timers-2-Pack/p.aspx
I put my busted power pack on a remote timer, but I like timers.
http://www.amazon.com/Woods-32555-Weatherproof-Outdoor-Converter/dp/B001Q9EFUK

My research into power pack issues resulted in tips for maintaining and setting up power packs.
The reason I add these tips now, before your power pack needs replacement is some fella wrote-in.
He bought 500 Watt power pack to replace 300 Watt > thinking bigger was better.
Power pack burned out. Here's why:
1) Match wattage of bulbs with wattage of power pack
-15 each X 20 watt bulbs = 300 watts, so install 300Watt power pack
2) Installing a 500W power pack on 300W of bulbs will burn out bulbs and power pack.
3) Replace bulbs as soon as they burn out or other bulbs will burn out and power pack will burn out.
4) When working on bulbs, unplug power pack or it may burn out.
http://www.malibulights.com/guides_support/low_voltage_planning_guide/select_your_power_pack

'Harry' wrote to me yesterday with handy malibu information.
1) Power packs come with 5 year limited warranty.
He is contacting Malibulights.com for a refund of some type.
Hope he writes back and says how that comes out.
2) He was having problem and plugged power pack into wall timer, then set timer.
Heh heh, pretty clever: Malibu transformer works, but timer doesn't, so plug power pack into a wall timer!!

That being said, I had same problem with my power pack.
I used blower to remove dirt and sprayed wd-40 and tried to take it apart.
My power pack was getting electricity.
Connections were good where lights tie into wire.
My lights never turned off.

Power pack doesn't come apart.
I turned it upside down thinking water got into timer.
I took it inside and let it warm up.
It still wouldn't work so bought another one.
Then I searched Intermatic and Malibulights.com for answer, but they have no troubleshooting or repair other than check electricity and check bulbs.
Conclusion: when power pack doesn't work, it is broken.
Unless you buy a separate timer and plug power pack into that timer as Harry suggests.

After researching power packs at Intermatic, Malubulights.com, ebay etc, the best I found were tips for next power pack that might save money:
The reason I add these tips now, before your power pack needs replacement is some fella wrote-in.
He bought 500 Watt power pack to replace 300 Watt > thinking bigger was better.
Power pack burned out. Here's why:
1) Match wattage of bulbs with wattage of power pack
-15 each X 20 watt bulbs = 300 watts, so install 300Watt power pack
2) Installing a 500W power pack on 300W of bulbs will burn out bulbs and power pack.
3) Replace bulbs as soon as they burn out or other bulbs will burn out and power pack will burn out.
4) When working on bulbs, unplug power pack or it may burn out.
http://www.malibulights.com/guides_support/low_voltage_planning_guide/select_your_power_pack

Below is link going to malibu.com manuals
http://www.malibulights.com/customer_service/owners_manuals.aspx

Below is link going to a guide for setting up your malibu lighting
http://www.malibulights.com/guides_support/low_voltage_planning_guide/select_your_power_pack.aspx

Let me save you some money:
1) Match up wattage of bulbs with wattage of power pack:
15 - 20 watt bulbs = 300 watts = 300 watt power pack ... if you buy the 500 watt power pack for 300Watts of bulbs, then it will burn up the power pack.
2) Replace bulbs as soon as they burn out or other bulbs will burn out and the power pack will burn out too
3) When working on bulbs, unplug power pack or the power pack may burn out

If you need more assistance, add a comment and I will answer

There is no fuse and no repair parts

I've been all over the Malibulights.com website looking for anything that might help the large number of people with Malibu questions. The website has very little information and no parts and the site offers no help except the following:

1) Malibu gets the customer money, and other people troubleshoot for their customers
2) When buying a power pack, the total bulb wattage on the line has to match the power pack wattage
10 - 20 watt bulbs = 200 Watt power pack
15 -20 watt bulbs = 300 Watt power pack
http://www.malibulights.com/guides_support/low_voltage_planning_guide/select_your_power_pack.aspx
If your power pack is oversized, it will burn out the bulbs and burn out the power pack

3) A power pack makes a humming noise when it has power >>> check your power source if power pack won't work >>> no other troubleshooting is offered
4) Replace burned out bulbs ASAP or the power pack burns out the other bulbs
5) Unplug power pack when working on bulbs [otherwise, the power pack burns out which is why people write fixya asking why their power pack won't work after replacing all their bulbs]
6) Nowhere on the Malibu site does it offer-or-explain burned out power packs or power packs that don't work, but they show plenty of new products for you to buy.

These dang power packs don't have replacement parts. You can see if the manual override turns lights on and off. The power pack makes a humming noise. If the timer is not rotating, then try setting the current time.

Malibu manuals are located on this page
Normal 0 false false false MicrosoftInternetExplorer4 http://www.malibulights.com/customer_service/owners_manuals.aspx

If you buy another one, be sure to match up total wattage of bulbs to the power pack wattage.
For example 10 - 20 watt bulbs = 200 Watts >> you should buy 200 Watt power pack
15 - 20 watt bulbs = 300 Watt power pack
Oversized power pack will burn out the bulbs
Also if you let bulbs burn out, it will shorten life of power pack
Unplug the power pack when working on the bulbs

Malibu product manuals
http://www.malibulights.com/customer_service/owners_manuals.aspx

Manual for 300 Watt power pack
http://malibulights.com/docs/pdf/8100-9300-01.pdf
Read cautions

Tips
300 Watt power pack requires sum of bulbs to equal 300 Watts
If you use 10 - 20 watt bulbs that is only 200 Watts so you need 200 Watt power pack

Replace burnt out bulbs immediately or other bulbs will burn out and shorten life of power pack
When working on bulbs, unplug power pack so it does not shorten life of power pack

Set Malibu Timer:
Red trippers are ON
Black trippers are OFF
Place trippers on dial at ON OFF times/ AM and PM

Set current time of day:
Plug in power pack
Trippers are installed
Rotate dial counter-clockwise to current time, say 9 am
Rotate dial 2 more revolutions and then return to current time
That's it

Malibu power pack has to match total watts of bulbs

15 bulbs each 20 watt = 300 Watt power pack
10 bulbs each 20 watt = 200 Watt power pack

Hello yes you can the Important thing to remember here is not to exceed the wattage that the transformer puts out.

Add up the wattage of each bulb that you are running and ensure that you do not exceed 300 watts.

for example a 300 watt transformer could drive
a. 10 - 30 watt bulbs
b. 20 - 15 watt bulbs
c 75 - 4 watt bulbs

Its also ok to mix bulb wattage for example I use 10 watt bulbs in the fixtures in the front of the house but also power 4 20watt spotlights from the same transformer.

Hope that helps