One of Wall Street's biggest bulls is bracing for more wild market swings.

With the S&P 500 and Dow off 4% from their all-time highs, Wells Fargo Securities' Christopher Harvey is worried fear over ultra-low U.S. rates and negative rates abroad could spark another deep sell-off.

"If you have a loss of confidence with the rate market, that's going to spill over into equities," the firm's head of equity strategy told CNBC's "Futures Now" last Thursday. "We really think rates are leading equities at this point in time… We think the rate market is exceptionally important at this point in time."

But Harvey believes it premature to wander into the bear camp.

Harvey's year-end S&P 500 remains 3,088. It reflects a 6% gain from Friday's close. Harvey is sticking with the target despite his call for investors to keep their eyes wide open.

In a recent note, he wrote: "We hear the frustration/despair from rates players — and that's not good because fear and loss of confidence fester. Best trader quote we've heard: 'It's a 'pencils down' moment.'"

Meanwhile, Harvey is still looking to put money to work. He's focused on picking up quality names at compelling prices — listing semiconductors, food, beverage and tobacco and some diversified financials as attractive groups. Harvey expects them to do well in an environment that's still exhibiting economic growth.

"[What] we can't lose sight of is the U.S. consumer is very, very solid," he said. "They're in a very good position. They have a job. They have savings. They have lower interest costs whether it's through mortgages or otherwise."

For a strategist who has said he's "not a real positive guy,' Harvey's bullishness should calm some frazzled nerves on the Street. He came into 2019 with the lowest S&P year-end price target on the Street. In late April, he turned bullish and never looked back.

"We're not in negative rate territory," Harvey said. "We have good valuation, lower rates and we have an underlying economy that's three yards and a cloud of dust."