Go the air horn route and use an air suspension pump for any of the GM products. These are available from wrecking yards and cost around $25. 00. The air horns I used was from Grover Products Company, (213) 263-9981. You will need some type of air reservoir, here again I went the lower cost route and used empty fire extinguishers. Plumed them together and added a pressure limit switch. Horns were part number 1601, 15 1/4" and 13 1/4" in length and mounted under the hood. They are "bomber loud" and have been great fun to use on people who haven't learned how to drive.
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98. 5 ISB 2500HD 4X4 SLT QC, 3. 54 forest green/camel leather, 5 spd. hood weather bra, cobra CB, Westech boost & pyro, Geno "A" pod, Dee Zee brds. Grover air horns, toaster LED's, HD light lens covers, bug deflector, J&J mud flaps, back up alarm, K&N, Guidon fiberglass tonneau, Ventvisors, Fuel door LED's, X-mission fltr. Fosgate/Clarion system, ABS, trailer tow, Aux rear suspension, factory clearance lamps, sliding rear window, Michelin LT265/75R16 LTX AT, RamZerks,