So... I have the dreaded turn signal fuse blowing issue with my 69 GS400, when the key is turned on. Notable options it has are: the 4-way power drivers seat (which works fine when tested outside of the car), power windows, power locks, console shifted automatic, AC, aftermarket radio, aftermarket tachometer, aftermarket oil pressure and water temperature gauges, and Petronix electronic ignition conversion. After reading a few other threads here about this, I started disconnecting circuits and items from the fuse box and harness, that are part of this circuit. So far I've disconnected the turn signal switch at the large connector under the column, the seat power wire at the seat and then at the fuse box, the tail light harness, the reverse light/neutral safety switch, the front turn signal lights, the tachometer power and light wires, the other gauge lights, and the engine and front light harnesses from the back of the fuse box at the firewall connector. I'm still getting continuity to ground on the power side of that fuse, at the fuse box. Effectively, I feel that I have isolated this short to the dash or intermediate harnesses, or something connected to them. Note that the battery is also completely disconnected too. It seems as though I am going to have to move the fuse box from the firewall, in order to access the intermediate harness connector. I'm pretty sure that is is the large connector above it. Those 51-year old connectors do not want to come apart too easily, either. If I have to pull the dash apart, I may consider replacing the dash harness and the intermediate harness, as I see that there are reproduction harness available from Lectric, American Autowire, and M & H. I would hate to go through all of that work and expense and still have this problem, though. I am going to lean on my new friends here at V8buick.com for some tips and suggestions first. I would really like to find the problem, before I order any new parts. Anything else I should look at that may be on this circuit and causing this problem? Any input, tricks, or tips on disassembling the dash and replacing that harness would be much appreciated, too. Thank you!
gsx-455-4ever, Thanks for posting those diagrams. The previous owner very genrously contributed the service manual that these came from, with the car. I can take these and print them to trace out the systems. Fairly quickly. The first time I drove it, the seat and turn signals didn't work. When I got home, I looked and the fuse was blown. I suspected the seat, so I disconnected and removed it, and put another fuse in. After cycling the key a few times, while fixing another issue, I noticed that it was blown again. Rather than putting another fuse in and blow it too, I checked and there was continuity on that circuit to ground. That's when I started unplugging things, trying to find the culprit.
I suggest looking at where the plug mates into the speedo assembly /circuit board for the dash lights.
Take one bulb out of one turn signal .. test (for fuse blowing), replace. try the other side then .. even try removing the light housing The turn signal housing itself is the ground through its connection to the bumper I once had an issue like this that drove me nutz .. turned out to be the power lead for the turn signal got "caught" on the mount. Took a couple of years for the insulation to wear out so it was dead shorting. If I had never taken the turn signal housing off I never would have found it
69GS400s, thank you for that input. This was one of the first things that I thought of after reading a few other threads about it. Right now the front light harness and the rear taillight harness are unplugged, and I still have the short to ground on the DIR SIG fuse location. I did find a complete wiring diagram for the car, on this forum, that someone had posted back in 2017. This and the circuit diagram from the manual that gsx-455-4ever posted, has given me some ideas on other components and circuits to test. Hopefully I can get some time tonight to work on it.
Does your meter beep when there is continuity? If so hitch it up to the grounded wire and start tapping and tugging on the harness until the beeping stops. Check the obvious spots first- hangers and any place the harness touches the body.
Just a little humor here : Its like when someone asks you , " Did you ever blow a stop sign ?? " and you say , "Yeah " , and the other persons asks , " How did you get it in your mouth ? " At least fuses are smaller and easier to blow . lol
Well... funny you should ask. I've been out working on the GS all day. When I was pulling the instrument panel, I noticed that the harness plug was not in it straight. When I unplugged the instrument panel and removed it (by the way, the process of getting it out is a royal PITA), I lost the continuity to ground on the DIR SIG BK UP fuse circuit. I tested the harness connector and there is no continuity to ground on any pin except #5, which is the ground/negative pin anyway. After removing all the light bulbs, clock, and fuel gauge from the instrument cluster, there is no continuity between any of the circuits and the chassis, except #5, which is OK. I'm pretty sure that the problem was with with the connector not in straight, and connected the #5 and #6 terminals together, causing the shorted circuit issue. #6 is for the left turn signal indicator. So, it looks like you (BuickV8Mike) had the winning suggestion! Thanks again. Since I have the instrument panel out, and it was such a chore to get out, I'm going to replace the printed circuit board (even though it tested OK it has a couple questionable looking spots), all of the light bulbs with LEDs, the headlight switch, and the cigarette lighter assembly before I put it back in. And, since I have the whole dash disassembled, I'm replacing the radio with a RestSound Long Beach unit, the glove compartment liner (I broke it), the glove compartment lock assembly (pre-broken), the flexible HVAC duct hoses, the flashers (with ground-able LED type), the front speakers, the right side courtesy light assembly, replacing all of the other dash light and courtesy light bulbs with LEDs, and if I can find one, the lower plastic AC duct. Also, if I can find a working clock, I may replace mine or find someone to rebuild the one I have, while I'm at it. It's also going to get new oil pressure and temperature gauges. The ones that the car came with work fine, they're just so small that it's hard to read them at a glance. I ordered 2 5/8 Autometer Sportcomp gauges and mounting cups before I started with this electrical issue journey.
Update... Well, I thought that I had found the culprit in the dash plug, but apparently that was not it. Yesterday I had most of the day to work on the car and started rebuilding the dash, installing the new speakers in the rear deck, and plugging things back in. While plugging things back in, I was testing that circuit to make sure that nothing re-appeared. The first thing I plugged in was the intermediate harness, and when I did it, the short seemed to come back. After unplugging it, it was still there. Frustrated as hell, I decided I was just going to pull the whole dash harness and inspect it on the table. I started removing it at the ends (first the fusebox end) and work my way to the middle. When I got to the console end of the harness, I found the the reverse light power wire (pink) was pinched in the mechanism for the floor shifter. Every time the shifter was in the park position it pinched this wire in the notch. After I moved it out of the notch, the short disappeared! So, after all of the work of taking the dash completely apart, it turns out that the problem was in the console/shifter. I must have not had a good connection with my meter or had the shifter in a different position, when I thought it was the dash harness plug... ugh. At least I can repair this wire without spending any more money!
