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Posted by: Dave97 Sep 22 2020, 05:41 PM

What is normal voltage drop when you turn on the lights? I’m just going off the volt meter, but I start at about 14.2 driving around, when I pull on even the first notch of the light switch I’ll drop to less than 13. Is it a ground issue? I understand that this a rather common. Thanks. Dave

Posted by: ClayPerrine Sep 22 2020, 06:45 PM

Ignore it. The voltmeter in the console of a 914 is about as accurate as a shotgun loaded with gravel. Use it as a general guide, not a precise instrument. If it starts trending downward, then worry.

Posted by: GregAmy Sep 22 2020, 06:46 PM

I took mine out, I hated it so much. The light on the dash gives you what you need to know.

Edit: and then, when you have big feet like me and you accidentally knock out the fuse, but don't notice the dead voltmeter until you're well away from home at night in the rain, and you panic and get all wet only to figure out it was just the fuse...out you go.

Posted by: porschetub Sep 22 2020, 09:20 PM

Don't trust mine but its sort of an indicator,but being wired off the centre console wiring and dash mounted most likely causing a false reading of 1V low which I have,another job on the list .

Posted by: davep Sep 22 2020, 09:32 PM

There is a fair current being distributed at the fusebox to run everything up front. As the load goes up, the resistance losses in the wiring cause the voltage to go down. Ever try to read the voltage at the starter when starting? Sometimes the voltage drops to 8. One thing to try is to run separate fused power from the battery to relays for the headlights. This takes a big load off of the old system and provides better voltage to the headlights. Similar is the addition of a relay near the starter to reduce the current through the ignition switch which often burns out; and it is hard to find good ignition switches these days.

Posted by: 76-914 Sep 22 2020, 10:33 PM

QUOTE(davep @ Sep 22 2020, 08:32 PM)

Posted by: lierofox Sep 23 2020, 01:11 PM

QUOTE(76-914 @ Sep 22 2020, 09:33 PM)

QUOTE(davep @ Sep 22 2020, 08:32 PM)

There is a fair current being distributed at the fusebox to run everything up front. As the load goes up, the resistance losses in the wiring cause the voltage to go down. Ever try to read the voltage at the starter when starting? Sometimes the voltage drops to 8. One thing to try is to run separate fused power from the battery to relays for the headlights. This takes a big load off of the old system and provides better voltage to the headlights. Similar is the addition of a relay near the starter to reduce the current through the ignition switch which often burns out; and it is hard to find good ignition switches these days.

Actually it’s very accurate if you run a dedicated wire from the battery to the gauge. Everyone in here has asked the same question when they got their 914.

Posted by: porschetub Sep 23 2020, 05:42 PM

QUOTE(76-914 @ Sep 23 2020, 04:33 PM)

QUOTE(davep @ Sep 22 2020, 08:32 PM)

There is a fair current being distributed at the fusebox to run everything up front. As the load goes up, the resistance losses in the wiring cause the voltage to go down. Ever try to read the voltage at the starter when starting? Sometimes the voltage drops to 8. One thing to try is to run separate fused power from the battery to relays for the headlights. This takes a big load off of the old system and provides better voltage to the headlights. Similar is the addition of a relay near the starter to reduce the current through the ignition switch which often burns out; and it is hard to find good ignition switches these days.

Actually it’s very accurate if you run a dedicated wire from the battery to the gauge. Everyone in here has asked the same question when they got their 914.

Posted by: Dave97 Sep 24 2020, 08:21 AM

Thanks everyone. I understand the age of the vehicle and that this is "normal". To be clear that the biggest drop to about 13 volts happens with just the parking lights on, not the headlights. Then with the headlights on, to less than 13. I have replaced the fuse box with the newer style. I don't know what I would have at night, in the rain with fog lights on. Is it a ground issue?

Posted by: davep Sep 24 2020, 09:12 AM

It could certainly be a ground issue. I had a 914 where starting was hard until I added a ground cable from battery post to the fan shroud; there is a handy hole (about 8mm) near where the coil mounts. While the ground stud on the wall near the battery seemed sound the body itself seemed to be the weak link in the grounding circuit. The transmission ground strap is a critical part of the ground system also; sometimes they need to be replaced just because. However, cleaning all major ground connections is very important. Remember that the alternator grounds to the fan shroud, and the starter grounds to the transmission case, so the engine and transmission need really good grounding to the chassis. A rusty chassis will not act as good as a ground as you might expect.
The parking lights should not drop the voltage significantly. That does indicate problems somewhere.

Posted by: steuspeed Sep 25 2020, 12:09 AM

[/quote]
That's what I did, I used the wire going to the voltmeter as the trigger for a relay coil. Through the relay I ran a wire directly from the battery to the volt meter. Voltage is perfectly accurate now regardless of what loads are on the system.
[/quote]

This is a great idea!

Posted by: Dave97 Sep 25 2020, 02:31 PM

Thanks everyone. What seems strange to me is the fact that the biggest voltage drop is just with the parking lights. In the past I have put relay's on a early 911 headlights to get direct power to them and not go thru the switch. I have checked the grounds at the headlight to the body and cleaned them. How do I check the "real" voltage? Do I need to verify the gauge? At an indicated 12.5 volts the headlights don't seem to dim. Suggestions?