New registered user here.

Im trying to use IQFeed data to run some intraday backtests but with no success.
Getting this error : "Error processing symbol AAPL DataSeries do not have equal number of values for mathematical operation"

Need help please.

It seems that i need a IQfeed subscription first. There's a free extension who provides intraday data that i can use for backtesting only?

Try the AlphaVantage extension. Follow the links on that page to AlphaVantage to get your API key first, and then to the wiki for important usage info.

Thanks but it's very limited. It only shows data for the last 3 months. Any other option?

In WL7 the Alphavantage provider will have an option to download all available intraday data (up to 2 years) even on their Free plan. By default it will get the limited intraday data, however. That's because of severe free plan limitations @ AV.

Please find your remaining options summarized here:

Map of Wealth-Lab 6 Data Providers

Basically you can install the Tiingo provider (with intraday IEX data, up to 10K bars) and start a free trial subscription to IQFeed.

P.S. On a related note, in WL7 there will be a new paid extension with upgraded Tiingo data provider which requests all available intraday data going back to 2017.