Temp gage and tach eratic (72 Bav)

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Buffarea

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I have worked on this car several days a week since I bought it in November, with the goal of being a daily driver. I am working on a documented thread which will cover what I have done and will post it soon.
I have been able to drive it for the last week or so but have noticed 4 electrical problems that I hope are somehow related to each other.
The (1) fuel gauge does not read at all sometimes but a smack on the dash pops it to life, the (2)tachometer seems to read normally at idle, but a throttle blip will cause it to drop or bounce around, and the (3) temp gauge reads normally most times but will jump/jiggle higher and higher but then suddenly drop to normal again. I have moved /jiggled wire looms while on but cannot reproduce the problems that way. And the (4) headlights do not come on, although all running/dash/brake and signals do work. (it should be noted that I do not have a highbeam switch, in case this abscence is related to the headlight issue)
I removed the dash cluster and checked all connections including ground and they look ok. In the process of having the lower panel off I was excited to find a loose connector in the ignition switch harness, but repaired it and no difference.

Can someone tell me the physical location of the ground for this loom? And or shed any advice?
 
Power to the low and high beam comes from the Hi/lo switch so without it you have no power to them. If `73 or earlier the high runs through a relay via a white wire, the low runs direct to the low beam via a yellow wire and neither is fused. I just added a relay to my low beam and used the yellow wire as the trigger for the relay. I plan to add a fuse under the column for the power to the hi/lo switch as well. Jumping tach is usually the tach wire on the back of the tach or the source which is from the coil negative terminal.

Although you have already checked, it still sounds like a poor ground or the leads into the back of the instruments. HTH.

Chris
 
I agree on the bad ground. I had the same problem with my '71 bav and all i did was run a ground wire off each gauge on the back nut. Works great!
 
rickysbmw320i said:
I agree on the bad ground. I had the same problem with my '71 bav and all i did was run a ground wire off each gauge on the back nut. Works great!
Click to expand...

hi

thanks for your help

can you explain a little where and how did you put an additional ground ?

may be if you can post a photo will be great to understand

regards
 
High & Low beams

In support of HB Chris' suggestion: If you add the low beam relay in the spare slot under the hood with the other relays, it's a very convenient place to cut into the low beam wire, and also take power from the battery.

Instead of putting a fuse under the dash for the high beam, use new relays with their own built-in spade-type fuses. Hella makes one- photo attached.
 

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oldcoupe said:
In support of HB Chris' suggestion: If you add the low beam relay in the spare slot under the hood with the other relays, it's a very convenient place to cut into the low beam wire, and also take power from the battery.

Instead of putting a fuse under the dash for the high beam, use new relays with their own built-in spade-type fuses. Hella makes one- photo attached.
Click to expand...

More detail please, I'm sure it will make sense eventually.
Reminder, I have no high/low beam switch. So as a temporary way to get some headlights, I find the 2 wires nesc. to get lows to function and connect them, with an inline fuse or relay?
Also note that when I find a correct switch , this will no longer be a problem, but $190.00 for one switch is not an option.
 
Thanks for the info., I wish I had read it this morning!
What I did was remove the speaker cover above the cluster and fish out the connector for the high/low switch. I determined the yellow/white power wire and the smaller double-white wires and connected them with a 15 amp fuse. This turned on high beams (with the headlight switch), so I unplugged both highbeams at the bulbs leaving only the outer bulbs illuminated.
It is my intention to replace the h/l beam switch asap, but want headlights in the meantime. All other lights function as they should.

Back to the gauge issue, I located both brown ground wires at the multipin plugs on the back of the cluster and ran two additional ground wires from them. Unfortunatly nothing has changed with gauges.
My next plan for the temp gauge is to replace the temp sensor and see what happens. My feeling at this point is that the tach may be bad, but more wire and connection checking is nescesary first.

Again, thanks for the help! Updates will follow.
 
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I replaced the coil today with a Bosch coil from a 88 Vw GTI, it starts and runs much better and the tach now works correctly at all rpms!
Also, the eratic temp gauge issue has been resolved by the eventual correct bleeding of the cooling system.

Thanks all for the help!
 
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