Exhibit (a)(1)(iv)

Offer To Purchase For Cash

All Outstanding Shares of Common Stock

(Including the Associated Stock Purchase Rights)

of

Technology Research Corporation

$7.20 Net Per Share

By

Clearwater Acquisition I, Inc.

A Wholly Owned Subsidiary of

Coleman Cable, Inc.

April 12, 2011

To Brokers, Dealers, Commercial Banks, Trust Companies and Other Nominees:

We have been engaged by Clearwater Acquisition I, Inc. (the “Purchaser”), a Florida corporation and a wholly owned subsidiary of Coleman Cable, Inc., a Delaware corporation, to act as Dealer Manager in connection with its offer to purchase all outstanding shares of common stock, par value $0.51 per share (together with the associated stock purchase rights, the “Shares”), of Technology Research Corporation, a Florida corporation (“TRC”), at $7.20 per Share, net to the seller in cash, without interest and less any required withholding taxes, upon the terms and subject to the conditions set forth in the Purchaser’s Offer to Purchase dated April 12, 2011, and the related Letter of Transmittal (which, together with any amendments or supplements thereto, collectively constitute the “Offer”).

The Offer is conditioned upon, among other things, there being validly tendered and not withdrawn before the expiration of the Offer a number of Shares which, together with the shares then owned by Coleman and its subsidiaries (including the Purchaser), represents at least 50.1% of the total number of shares outstanding on a fully diluted basis.

For your information and for forwarding to your clients for whom you hold Shares registered in your name or in the name of your nominee, we are enclosing the following documents:

1. Offer to Purchase dated April 12, 2011;

2. Letter of Transmittal, including a Substitute Form W-9, for your use and for the information of your clients;

3. Notice of Guaranteed Delivery to be used to accept the Offer if the Shares and all other required documents cannot be delivered to BNY Mellon Shareowner Services, the Depositary for the Offer, or if the procedures for book-entry transfer cannot be completed, by the expiration of the Offer;

4. A form of letter which may be sent to your clients for whose accounts you hold Shares registered in your name or in the name of your nominee, with space provided for obtaining such clients’ instructions with regard to the Offer;

5. Guidelines for Certification of Taxpayer Identification Number on Substitute Form W-9 providing information relating to backup withholding of U.S. federal income tax; and

6. Return envelope addressed to the Depositary.

YOUR PROMPT ACTION IS REQUIRED. WE URGE YOU TO CONTACT YOUR CLIENTS AS PROMPTLY AS POSSIBLE.

THE OFFER AND WITHDRAWAL RIGHTS EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY TIME, ON FRIDAY, MAY 13, 2011, UNLESS THE OFFER IS EXTENDED.

The Purchaser will not pay any fees or commissions to any broker, dealer or other person (other than the Dealer Manager, the Information Agent or the Depositary as described in the Offer to Purchase) for soliciting

tenders of Shares pursuant to the Offer. However, the Purchaser will, upon request, reimburse brokers, dealers, banks and trust companies for reasonable and necessary costs and expenses incurred by them in forwarding materials to their customers. The Purchaser will pay all stock transfer taxes applicable to its purchase of Shares pursuant to the Offer, subject to Instruction 6 of the Letter of Transmittal. Under no circumstances will interest be paid on the purchase price for the Shares, regardless of any extension of or amendment to the Offer or any delay in making payment for the Shares.

In order to accept the Offer, a duly executed and properly completed Letter of Transmittal and any required signature guarantees, or an Agent’s Message (as defined in the Offer to Purchase) in connection with a book-entry delivery of Shares, and any other required documents, must be sent to the Depositary by 12:00 Midnight, New York City time, on Friday, May 13, 2011.

Any inquiries you may have with respect to the Offer should be addressed to the Information Agent or the undersigned, and additional copies of the enclosed materials may be obtained from the Information Agent, at the addresses and telephone numbers set forth on the back cover of the Offer to Purchase.

Very truly yours,

WILLIAM BLAIR & COMPANY, L.L.C.

NOTHING CONTAINED HEREIN OR IN THE ENCLOSED DOCUMENTS SHALL CONSTITUTE YOU THE AGENT OF CLEARWATER ACQUISITION I, INC., COLEMAN CABLE, INC., THE DEALER MANAGER, THE INFORMATION AGENT OR THE DEPOSITARY, OR AUTHORIZE YOU OR ANY OTHER PERSON TO USE ANY DOCUMENT OR MAKE ANY STATEMENT ON BEHALF OF ANY OF THEM IN CONNECTION WITH THE OFFER OTHER THAN THE DOCUMENTS ENCLOSED HEREWITH AND THE STATEMENTS CONTAINED THEREIN.

2