1985 gmc radio questions - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Ralph's '85 · 04-15-2016, 12:49 PM

Hi,
I have a 1985 Sierra with the stock radio. It didn't work at first, turns out the fuse was blown so I replaced it and it worked. But when I drive the truck the fuse blows every time even if the radio is off. I am using a 15 amp fuse. Is this the correct size? Thanks

ranger danger · 04-15-2016, 03:40 PM

Sounds like its grounding out somewhere. Most basic radios don't need more than 7 amp fuses.

Ralph's '85 · 04-15-2016, 05:06 PM

The weird thing is the fuse will only blow when driving in overdrive (700r4). Regular drive is fine. Any ideas?

ray_mcavoy · 04-15-2016, 07:58 PM

Yes, 15 amp is the correct size fuse for this circuit because it powers more than just the radio. This circuit also powers the 3 "ACC" (accessory) receptacles in the fuse box. Those are used to supply power to various options such as the 700R4 lock-up torque converter solenoid, 4 wheel drive indicator light, and auxiliary battery relay.

I can't find many details on the 700R4 wiring in the 1985 wiring diagrams but the 1986 diagrams have some info. It appears as though many of them have a switch inside the transmission that closes when the 4th clutch (overdrive) is engaged. That feeds power to the torque converter clutch solenoid which should have a resistance of 23.5Ω. So a short to ground in the wiring (internal to the trans) between that switch & the solenoid or a shorted solenoid are a couple possibilities that could cause the radio fuse to blow only when the trans is operated in overdrive.

04-15-2016, 12:49 PM	#1
Ralph's '85 Registered User Join Date: Jan 2016 Location: CT Posts: 2	1985 gmc radio questions Hi, I have a 1985 Sierra with the stock radio. It didn't work at first, turns out the fuse was blown so I replaced it and it worked. But when I drive the truck the fuse blows every time even if the radio is off. I am using a 15 amp fuse. Is this the correct size? Thanks

04-15-2016, 03:40 PM	#2
ranger danger Registered User Join Date: Jan 2015 Location: Vacaville CA Posts: 896	Re: 1985 gmc radio questions Sounds like its grounding out somewhere. Most basic radios don't need more than 7 amp fuses. __________________ 1969 C20 Suburban "Rez Dog" Rebuild America one testicle at a time. US Army 1977-1979 12B Combat Engineer US Navy 1979-1983 Gunners Mate Guns (GMG) NRA Life Member Unrestrained Children in back seats cause Accidents. Unrestrained Accidents in back seats cause Children.

04-15-2016, 05:06 PM	#3
Ralph's '85 Registered User Join Date: Jan 2016 Location: CT Posts: 2	Re: 1985 gmc radio questions The weird thing is the fuse will only blow when driving in overdrive (700r4). Regular drive is fine. Any ideas?

04-15-2016, 07:58 PM	#4
ray_mcavoy Registered User Join Date: Nov 2009 Location: Sherman, ME Posts: 2,354	Re: 1985 gmc radio questions Yes, 15 amp is the correct size fuse for this circuit because it powers more than just the radio. This circuit also powers the 3 "ACC" (accessory) receptacles in the fuse box. Those are used to supply power to various options such as the 700R4 lock-up torque converter solenoid, 4 wheel drive indicator light, and auxiliary battery relay. I can't find many details on the 700R4 wiring in the 1985 wiring diagrams but the 1986 diagrams have some info. It appears as though many of them have a switch inside the transmission that closes when the 4th clutch (overdrive) is engaged. That feeds power to the torque converter clutch solenoid which should have a resistance of 23.5Ω. So a short to ground in the wiring (internal to the trans) between that switch & the solenoid or a shorted solenoid are a couple possibilities that could cause the radio fuse to blow only when the trans is operated in overdrive.



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