<PAGE>
 
                                                                HEI Exhibit 99.2
                                                                ----------------



                  EIGHTH AMENDMENT TO TRUST AGREEMENT BETWEEN
                     FIDELITY MANAGEMENT TRUST COMPANY AND
                       HAWAIIAN ELECTRIC INDUSTRIES, INC.

     THIS EIGHTH AMENDMENT TO TRUST AGREEMENT, is made and entered into
February 27, 1998, by and between Fidelity Management Trust Company (the
"Trustee") and Hawaiian Electric Industries, Inc. (the "Sponsor");

                                  WITNESSETH:

     WHEREAS, the Trustee and the Sponsor heretofore entered into a Trust
Agreement dated November 28, 1988, and amended December 22, 1989, January 1,
1994, March 15, 1994, February 1, 1996, April 1, 1996, April 1, 1997 and June
13, 1997 (the "Trust Agreement") for the Hawaiian Electric Industries Retirement
Savings Plan (the "Plan"); and

     WHEREAS, the Trustee and the Sponsor wish to further amend said Trust
Agreement as provided in Section 13 thereunder; and

     WHEREAS, on February 27, 1998, the Sponsor wishes to add as an investment
option under the Plan, the Fidelity U.S. Bond Index Fund; and

     WHEREAS, on July 1, 1998, the Sponsor wishes to remove as an investment
option under the Plan, the Fidelity International Bond Fund; and

     WHEREAS, the Sponsor now desires, and hereby directs the Trustee, in
accordance with Sections 4(b) and 7(c), to liquidate all participant balances
held in Fidelity International Bond Fund on July 1, 1998, and to invest the
proceeds in the ASB Money Market Account until such time as the affected
participants direct that the proceeds be invested in other investment options
offered under the Plan.  The parties hereto agree that the Trustee shall have no
discretionary authority with respect to this sale and transfer directed by the
Sponsor.  Any variation from the procedure described herein may be instituted
only at the express written direction of the Sponsor; and

     NOW THEREFORE, in consideration of the above premises the Trustee and the
Sponsor hereby amend the Trust Agreement by:

     (1)  Amending and restating Schedules "A" and "C" as attached.
 
     IN WITNESS WHEREOF, the Trustee and the Sponsor have caused this Eighth
Amendment to be executed by their duly authorized officers effective as of the
day and year first above written.

HAWAIIAN ELECTRIC INDUSTRIES, INC.    FIDELITY MANAGEMENT TRUST
BY:  HAWAIIAN ELECTRIC INDUSTRIES,    COMPANY
INC. PENSION INVESTMENT COMMITTEE
 

By /s/ Robert F. Mougeot  2/23/98    By /s/ Cheryl L. Gladstone  3/4/98
   ---------------------  -------       -----------------------  ------
  Robert F. Mougeot       Date          Vice President           Date
  Chairman


By /s/ Constance H. Lau  2/20/98
   --------------------  -------
  Constance H. Lau        Date
  Secretary and Member
<PAGE>
 
                                  SCHEDULE "A"
                                        
                            ADMINISTRATIVE SERVICES
                            -----------------------

Administration
--------------

     * Establishment and maintenance of Participant account and election
percentages.

     * Maintenance of the following plan investment options:

            - Fidelity Retirement Money Market Portfolio                    
            - ASB Money Market Account                                      
            - HEI Common Stock Fund                                         
            - Fidelity Puritan Fund                                         
            - Fidelity Magellan Fund                                        
            - Fidelity Overseas Fund                                        
            - Fidelity International Bond Fund (formerly known as Fidelity 
              Global Bond Fund)(to 6/30/98)                       
            - Fidelity Freedom 2000 Fund                                   
            - Fidelity Freedom 2010 Fund                          
            - Fidelity Freedom 2020 Fund                          
            - Fidelity Freedom 2030 Fund                          
            - Fidelity Freedom Income Fund                        
            - Spartan U.S. Equity Index Fund (formerly known as Fidelity U.S.
              Equity Index Portfolio)                                        
            - MAS Value Portfolio                                            
            - Neuberger & Berman Partners Trust                              
            - PBHG Emerging Growth Fund                                      
            - Fidelity U.S. Bond Index Fund                                  

     * Maintenance of the following money classifications:

            - Salary Reduction                
            - Participant Voluntary           
            - Rollover                        
            - HEI Diversified Plan            
            - Employer ASB                    
            - Employer Supplemental           
            - IRA                             
            - Voluntary HEISOP                
            - Employer HEISOP                  

     * Processing of investment option trades.

     The Trustee will provide only the recordkeeping and administrative services
set forth on this Schedule "A" and no others.

                                       2
<PAGE>
 
Processing
----------

     * Weekly processing of contribution data and contributions
     * Processing of transfers and changes of future allocations via the
       telephone exchange system
     * Daily processing of withdrawals

 
Other
-----

     * Monthly trial balance
     * Quarterly administrative reports
     * Quarterly participant statements
     * 1099Rs and W-2Ps
     * Participant Loans
     * Periodic meetings with Sponsor
     * Educational services as needed and mutually agreed upon by the Trustee
       and the Sponsor.


HAWAIIAN ELECTRIC INDUSTRIES, INC.      FIDELITY MANAGEMENT TRUST
BY:  HAWAIIAN ELECTRIC INDUSTRIES,      COMPANY
INC. PENSION INVESTMENT COMMITTEE
 
 
By /s/ Robert F. Mougeot      2/23/98   By /s/ Cheryl L. Gladstone   3/4/98
   ---------------------      -------   --------------------------   ------
     Robert F. Mougeot        Date      Vice President               Date
     Chairman
 
By /s/ Constance H. Lau       2/20/98
   ---------------------      -------
     Constance H. Lau         Date
     Secretary and Member

                                       3
<PAGE>
 
                                  SCHEDULE "C"
                                        
                               INVESTMENT OPTIONS
                               ------------------


     In accordance with Section 4(b), the Named Fiduciary hereby directs the
Trustee that participants' individual accounts may be invested in the following
investment options:

     - Fidelity Retirement Money Market Portfolio
     - ASB Money Market Account
     - HEI Common Stock Fund
     - Fidelity Puritan Fund
     - Fidelity Magellan Fund
     - Fidelity Overseas Fund
     - Fidelity International Bond Fund (formerly known as Fidelity Global Bond
       Fund) (to 6/30/98)
     - Fidelity Freedom 2000 Fund
     - Fidelity Freedom 2010 Fund
     - Fidelity Freedom 2020 Fund
     - Fidelity Freedom 2030 Fund
     - Fidelity Freedom Income Fund
     - Spartan U.S. Equity Index Fund (formerly known as Fidelity U.S.
       Equity Index Portfolio)
     - MAS Value Portfolio
     - Neuberger & Berman Partners Trust
     - PBHG Emerging Growth Fund
     - Fidelity U.S. Bond Index Fund

     The investment option referred to in Section 4(c) and Section 4(d)(v)(B)(5)
shall be the ASB Money Market Account.

 
HAWAIIAN ELECTRIC INDUSTRIES, INC.
BY:  HAWAIIAN ELECTRIC INDUSTRIES,
INC. PENSION INVESTMENT COMMITTEE
 

By /s/ Robert F. Mougeot  2/23/98
   ---------------------  -------
  Robert F. Mougeot       Date
  Chairman

By /s/ Constance H. Lau  2/20/98
   --------------------  -------
  Constance H. Lau       Date
  Secretary and Member

                                       4